History of evolutionary thought - AbsoluteAstronomy.com

Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...

ary thought, the conception that species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

change over time, has roots in antiquity, in the ideas of the ancient Greeks

Ancient Greece

Ancient Greece is a civilization belonging to a period of Greek history that lasted from the Archaic period of the 8th to 6th centuries BC to the end of antiquity. Immediately following this period was the beginning of the Early Middle Ages and the Byzantine era. Included in Ancient Greece is the...

, Romans

Ancient Rome

Ancient Rome was a thriving civilization that grew on the Italian Peninsula as early as the 8th century BC. Located along the Mediterranean Sea and centered on the city of Rome, it expanded to one of the largest empires in the ancient world....

, and Chinese as well as in medieval Islamic science. However, with the beginnings of biological taxonomy

Biological classification

Biological classification, or scientific classification in biology, is a method to group and categorize organisms by biological type, such as genus or species. Biological classification is part of scientific taxonomy....

in the late 17th century, Western biological thinking was influenced by essentialism

Essentialism

In philosophy, essentialism is the view that, for any specific kind of entity, there is a set of characteristics or properties all of which any entity of that kind must possess. Therefore all things can be precisely defined or described...

, the belief that every species has essential characteristics that are unalterable, a concept from medieval Aristotelian

Scholasticism

Scholasticism is a method of critical thought which dominated teaching by the academics of medieval universities in Europe from about 1100–1500, and a program of employing that method in articulating and defending orthodoxy in an increasingly pluralistic context...

metaphysics

Metaphysics

Metaphysics is a branch of philosophy concerned with explaining the fundamental nature of being and the world, although the term is not easily defined. Traditionally, metaphysics attempts to answer two basic questions in the broadest possible terms:...

that fit well with natural theology

Natural theology

Natural theology is a branch of theology based on reason and ordinary experience. Thus it is distinguished from revealed theology which is based on scripture and religious experiences of various kinds; and also from transcendental theology, theology from a priori reasoning.Marcus Terentius Varro ...

. On the other hand as the Enlightenment

Age of Enlightenment

The Age of Enlightenment was an elite cultural movement of intellectuals in 18th century Europe that sought to mobilize the power of reason in order to reform society and advance knowledge. It promoted intellectual interchange and opposed intolerance and abuses in church and state...

progressed evolutionary cosmology and the mechanical philosophy spread from the physical sciences to natural history. Naturalists began to focus on the variability of species; the emergence of paleontology

Paleontology

Paleontology "old, ancient", ὄν, ὀντ- "being, creature", and λόγος "speech, thought") is the study of prehistoric life. It includes the study of fossils to determine organisms' evolution and interactions with each other and their environments...

with the concept of extinction

Extinction

In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...

further undermined the static view of nature. In the early 19th century, Jean-Baptiste Lamarck

Jean-Baptiste Lamarck

Jean-Baptiste Pierre Antoine de Monet, Chevalier de la Marck , often known simply as Lamarck, was a French naturalist...

proposed his theory of the transmutation of species

Transmutation of species

Transmutation of species was a term used by Jean Baptiste Lamarck in 1809 for his theory that described the altering of one species into another, and the term is often used to describe 19th century evolutionary ideas that preceded Charles Darwin's theory of natural selection...

, the first fully formed theory of evolution

Evolution

.

In 1858, Charles Darwin

Charles Darwin

Charles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...

and Alfred Russel Wallace

Alfred Russel Wallace

Alfred Russel Wallace, OM, FRS was a British naturalist, explorer, geographer, anthropologist and biologist...

published a new evolutionary theory that was explained in detail in Darwin's On the Origin of Species (1859). Unlike Lamarck, Darwin proposed common descent

Common descent

In evolutionary biology, a group of organisms share common descent if they have a common ancestor. There is strong quantitative support for the theory that all living organisms on Earth are descended from a common ancestor....

and a branching tree of life

Tree of life (science)

Charles Darwin proposed that phylogeny, the evolutionary relatedness among species through time, was expressible as a metaphor he termed the Tree of Life...

. The theory was based on the idea of natural selection

Natural selection

Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....

, and it synthesized a broad range of evidence from animal husbandry, biogeography, geology, morphology, and embryology.

The debate over Darwin's work led to the rapid acceptance of the general concept of evolution, but the specific mechanism he proposed, natural selection, was not widely accepted until it was revived by developments in biology that occurred during 1920s through the 1940s. Before that time most biologists argued that other factors were responsible for evolution. Alternatives to natural selection suggested during "the eclipse of Darwinism" (circa 1880 to 1920) included inheritance of acquired characteristics

Inheritance of acquired characters

The inheritance of acquired characteristics is a hypothesis that physiological changes acquired over the life of an organism may be transmitted to offspring...

(neo-Lamarckism), an innate drive for change (orthogenesis

Orthogenesis

Orthogenesis, orthogenetic evolution, progressive evolution or autogenesis, is the hypothesis that life has an innate tendency to evolve in a unilinear fashion due to some internal or external "driving force". The hypothesis is based on essentialism and cosmic teleology and proposes an intrinsic...

), and sudden large mutations (saltationism

Saltation (biology)

In biology, ""saltation"" is a sudden change from one generation to the next, that is large, or very large, in comparison with the usual variation of an organism...

). The synthesis of natural selection with Mendelian genetics

Mendelian inheritance

Mendelian inheritance is a scientific description of how hereditary characteristics are passed from parent organisms to their offspring; it underlies much of genetics...

during the 1920s and 1930s founded the new discipline of population genetics

Population genetics

Population genetics is the study of allele frequency distribution and change under the influence of the four main evolutionary processes: natural selection, genetic drift, mutation and gene flow. It also takes into account the factors of recombination, population subdivision and population...

. Throughout the 1930s and 1940s, population genetics became integrated with other biological fields, resulting in a widely applicable theory of evolution that encompassed much of biology—the modern evolutionary synthesis

Modern evolutionary synthesis

The modern evolutionary synthesis is a union of ideas from several biological specialties which provides a widely accepted account of evolution...

.

Following the establishment of evolutionary biology, studies of mutation

Mutation

In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...

and variation

Genetic diversity

Genetic diversity, the level of biodiversity, refers to the total number of genetic characteristics in the genetic makeup of a species. It is distinguished from genetic variability, which describes the tendency of genetic characteristics to vary....

in natural populations, combined with biogeography

Biogeography

Biogeography is the study of the distribution of species , organisms, and ecosystems in space and through geological time. Organisms and biological communities vary in a highly regular fashion along geographic gradients of latitude, elevation, isolation and habitat area...

and systematics

Systematics

Biological systematics is the study of the diversification of terrestrial life, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees...

, led to sophisticated mathematical and causal models of evolution. Paleontology and comparative anatomy

Comparative anatomy

Comparative anatomy is the study of similarities and differences in the anatomy of organisms. It is closely related to evolutionary biology and phylogeny .-Description:...

allowed more detailed reconstructions of the history of life. After the rise of molecular genetics

Molecular genetics

Molecular genetics is the field of biology and genetics that studies the structure and function of genes at a molecular level. The field studies how the genes are transferred from generation to generation. Molecular genetics employs the methods of genetics and molecular biology...

in the 1950s, the field of molecular evolution

Molecular evolution

Molecular evolution is in part a process of evolution at the scale of DNA, RNA, and proteins. Molecular evolution emerged as a scientific field in the 1960s as researchers from molecular biology, evolutionary biology and population genetics sought to understand recent discoveries on the structure...

developed, based on protein sequences and immunological tests, and later incorporating RNA and DNA studies. The gene-centered view of evolution

Gene-centered view of evolution

The gene-centered view of evolution, gene selection theory or selfish gene theory holds that evolution occurs through the differential survival of competing genes, increasing the frequency of those alleles whose phenotypic effects successfully promote their own propagation, with gene defined as...

rose to prominence in the 1960s, followed by the neutral theory of molecular evolution

Neutral theory of molecular evolution

The neutral theory of molecular evolution states that the vast majority of evolutionary changes at the molecular level are caused by random drift of selectively neutral mutants . The theory was introduced by Motoo Kimura in the late 1960s and early 1970s...

, sparking debates over adaptationism

Adaptationism

Adaptationism is a set of methods in the evolutionary sciences for distinguishing the products of adaptation from traits that arise through other processes. It is employed in fields such as ethology and evolutionary psychology that are concerned with identifying adaptations...

, the units of selection

Unit of selection

A unit of selection is a biological entity within the hierarchy of biological organisation that is subject to natural selection...

, and the relative importance of genetic drift

Genetic drift

Genetic drift or allelic drift is the change in the frequency of a gene variant in a population due to random sampling.The alleles in the offspring are a sample of those in the parents, and chance has a role in determining whether a given individual survives and reproduces...

versus natural selection. In the late 20th century, DNA sequencing led to molecular phylogenetics

Molecular phylogeny

Molecular phylogenetics is the analysis of hereditary molecular differences, mainly in DNA sequences, to gain information on an organism's evolutionary relationships. The result of a molecular phylogenetic analysis is expressed in a phylogenetic tree...

and the reorganization of the tree of life into the three-domain system

Three-domain system

The three-domain system is a biological classification introduced by Carl Woese in 1977 that divides cellular life forms into archaea, bacteria, and eukaryote domains. In particular, it emphasizes the separation of prokaryotes into two groups, originally called Eubacteria and Archaebacteria...

. In addition, the newly recognized factors of symbiogenesis

Symbiogenesis

Symbiogenesis is the merging of two separate organisms to form a single new organism. The idea originated with Konstantin Mereschkowsky in his 1926 book Symbiogenesis and the Origin of Species, which proposed that chloroplasts originate from cyanobacteria captured by a protozoan...

and horizontal gene transfer

Horizontal gene transfer

Horizontal gene transfer , also lateral gene transfer , is any process in which an organism incorporates genetic material from another organism without being the offspring of that organism...

introduced yet more complexity into evolutionary theory. Discoveries in evolutionary biology have made a significant impact not just within the traditional branches of biology, but also in other academic disciplines (e.g., anthropology

Evolutionary anthropology

Evolutionary anthropology is the interdisciplinary study of evolution of human physiology and human behaviour and the relation between hominids and non-hominid primates. Evolutionary anthropology is based in natural science and social science...

and psychology

Evolutionary psychology

Evolutionary psychology is an approach in the social and natural sciences that examines psychological traits such as memory, perception, and language from a modern evolutionary perspective. It seeks to identify which human psychological traits are evolved adaptations, that is, the functional...

) and on society at large.

Greeks

Proposals that one type of animal, even humans, could descend from other types of animals, are known to go back to the first pre-Socratic

Pre-Socratic philosophy

Pre-Socratic philosophy is Greek philosophy before Socrates . In Classical antiquity, the Presocratic philosophers were called physiologoi...

Greek philosophers

Greek philosophy

Ancient Greek philosophy arose in the 6th century BCE and continued through the Hellenistic period, at which point Ancient Greece was incorporated in the Roman Empire...

. Anaximander of Miletus (c.610–546 BC) proposed that the first animals lived in water, during a wet phase of the Earth's past, and that the first land-dwelling ancestors of mankind must have been born in water, and only spent part of their life on land. He also argued that the first human of the form known today must have been the child of a different type of animal, because man needs prolonged nursing to live. Empedocles

Empedocles

Empedocles was a Greek pre-Socratic philosopher and a citizen of Agrigentum, a Greek city in Sicily. Empedocles' philosophy is best known for being the originator of the cosmogenic theory of the four Classical elements...

(c. 490–430 BC), argued that what we call birth and death in animals are just the mingling and separations of elements which cause the countless "tribes of mortal things". Specifically, the first animals and plants were like disjointed parts of the ones we see today, some of which survived by joining in different combinations, and then intermixing, and wherever "everything turned out as it would have if it were on purpose, there the creatures survived, being accidentally compounded in a suitable way". Other philosophers, who became more influential in the Middle Ages, believed that the species of all things, not only living things, were fixed by divine design.

Plato

Plato , was a Classical Greek philosopher, mathematician, student of Socrates, writer of philosophical dialogues, and founder of the Academy in Athens, the first institution of higher learning in the Western world. Along with his mentor, Socrates, and his student, Aristotle, Plato helped to lay the...

(c. 428–348 BC) was called by biologist Ernst Mayr "the great antihero of evolutionism", because he promoted belief in essentialism

Essentialism

, which is also referred to as the Theory of Forms

Theory of Forms

Plato's theory of Forms or theory of Ideas asserts that non-material abstract forms , and not the material world of change known to us through sensation, possess the highest and most fundamental kind of reality. When used in this sense, the word form is often capitalized...

. This theory holds that each natural type of object in the observed world is an imperfect manifestation of the ideal, form or "species" which defines that type. In his Timaeus
Timaeus (dialogue)
Timaeus is one of Plato's dialogues, mostly in the form of a long monologue given by the title character, written circa 360 BC. The work puts forward speculation on the nature of the physical world and human beings. It is followed by the dialogue Critias.Speakers of the dialogue are Socrates,...

for example, Plato has a character tell a story that the Demiurge

Demiurge

The demiurge is a concept from the Platonic, Neopythagorean, Middle Platonic, and Neoplatonic schools of philosophy for an artisan-like figure responsible for the fashioning and maintenance of the physical universe. The term was subsequently adopted by the Gnostics...

created the cosmos

Cosmos

In the general sense, a cosmos is an orderly or harmonious system. It originates from the Greek term κόσμος , meaning "order" or "ornament" and is antithetical to the concept of chaos. Today, the word is generally used as a synonym of the word Universe . The word cosmos originates from the same root...

and everything in it because, being good, and hence, "... free from jealousy, He desired that all things should be as like Himself as they could be". The creator created all conceivable forms of life, since "... without them the universe will be incomplete, for it will not contain every kind of animal which it ought to contain, if it is to be perfect". This "plenitude principle

Plenitude principle

The plenitude principle or principle of plenitude asserts that everything that can happen will happen.The historian of ideas Arthur Lovejoy was the first to discuss this philosophically important Principle explicitly, it back to Aristotle, who said that no possibilities which remain eternally...

"—the idea that all potential forms of life are essential to a perfect creation—greatly influenced Christian

Christianity

Christianity is a monotheistic religion based on the life and teachings of Jesus as presented in canonical gospels and other New Testament writings...

thought. However some historians of science have questioned how much influence Plato's essentialism had on natural philosophy by stating that many philosophers after Plato believed that species might be capable of transformation and that the idea that biologic species were fixed and possessed unchangeable essential characteristics did not become important until the beginning of biologic taxonomy

Taxonomy

Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...

in the 17th and 18th centuries.

Aristotle

Aristotle

Aristotle was a Greek philosopher and polymath, a student of Plato and teacher of Alexander the Great. His writings cover many subjects, including physics, metaphysics, poetry, theater, music, logic, rhetoric, linguistics, politics, government, ethics, biology, and zoology...

(384–322 BC), the most influential of the Greek philosophers in Europe in the Middle Ages, was a student of Plato and is also the earliest natural historian whose work has been preserved in any real detail. His writings on biology resulted from his research into natural history on and around the isle of Lesbos

Lesbos Island

Lesbos is a Greek island located in the northeastern Aegean Sea. It has an area of with 320 kilometres of coastline, making it the third largest Greek island. It is separated from Turkey by the narrow Mytilini Strait....

, and have survived in the form of four books, usually known by their Latin

Latin

Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

names, De anima
On the Soul
On the Soul is a major treatise by Aristotle on the nature of living things. His discussion centres on the kinds of souls possessed by different kinds of living things, distinguished by their different operations...

(on the essence of life), Historia animalium
History of Animals
History of Animals is a zoological natural history text by Aristotle.-Arabic translation:The Arabic translation of Historia Animalium comprises treatises 1-10 of the Kitāb al-Hayawān .-See also:...

(inquiries about animals), De generatione animalium
Generation of Animals
The Generation of Animals is a text by Aristotle.-Arabic translation:...

(reproduction), and De partibus animalium (anatomy). Aristotle's works contain some remarkably astute observations and interpretations—along with sundry myths and mistakes—reflecting the uneven state of knowledge during his time. However, for Charles Singer

Charles Singer

Charles Joseph Singer was a British historian of science, technology, and medicine.-Early years:Singer was born in Camberwell in London, where his father Simeon Singer was a minister and Hebraist. He was educated at City of London School, University College London, and Magdalen College, Oxford...

, "Nothing is more remarkable than [Aristotle's] efforts to [exhibit] the relationships of living things as a scala naturæ." This scala naturæ, described in Historia animalium, classified organisms in relation to a hierarchical "Ladder of Life" or "Chain of Being", placing them according to their complexity of structure and function, with organisms that showed greater vitality and ability to move described as "higher organisms". Aristotle believed that features of living organisms showed clearly that they must have had what he called a final cause, that is to say that they had been designed for a purpose. He explicitly rejected the view of Empedocles that living creatures might have originated by chance.

Other Greek philosophers, such as Zeno of Citium

Zeno of Citium

Zeno of Citium was a Greek philosopher from Citium . Zeno was the founder of the Stoic school of philosophy, which he taught in Athens from about 300 BC. Based on the moral ideas of the Cynics, Stoicism laid great emphasis on goodness and peace of mind gained from living a life of virtue in...

(334–262 BC) the founder of the Stoic school of philosophy, agreed with Aristotle and other earlier philosophers that nature showed clear evidence of being designed for a purpose; this view is known as teleology

Teleology

A teleology is any philosophical account which holds that final causes exist in nature, meaning that design and purpose analogous to that found in human actions are inherent also in the rest of nature. The word comes from the Greek τέλος, telos; root: τελε-, "end, purpose...

. The Roman stoic philosopher Cicero

Cicero

Marcus Tullius Cicero , was a Roman philosopher, statesman, lawyer, political theorist, and Roman constitutionalist. He came from a wealthy municipal family of the equestrian order, and is widely considered one of Rome's greatest orators and prose stylists.He introduced the Romans to the chief...

wrote that Zeno was known to have held the view, central to Stoic physics, that nature is primarily "directed and concentrated… to secure for the world… the structure best fitted for survival."

Chinese

Ancient Chinese thinkers

Chinese philosophy

Chinese philosophy is philosophy written in the Chinese tradition of thought. The majority of traditional Chinese philosophy originates in the Spring and Autumn and Warring States era, during a period known as the "Hundred Schools of Thought", which was characterized by significant intellectual and...

such as Zhuangzi

Zhuangzi

Zhuangzi was an influential Chinese philosopher who lived around the 4th century BCE during the Warring States Period, a period corresponding to the philosophical summit of Chinese thought — the Hundred Schools of Thought, and is credited with writing—in part or in whole—a work known by his name,...

(Chuang Tzu), a Taoist philosopher who lived around the 4th century BC, expressed ideas on changing biologic species. According to Joseph Needham

Joseph Needham

Noel Joseph Terence Montgomery Needham, CH, FRS, FBA , also known as Li Yuese , was a British scientist, historian and sinologist known for his scientific research and writing on the history of Chinese science. He was elected a fellow of the Royal Society in 1941, and as a fellow of the British...

, Taoism

Taoism

Taoism refers to a philosophical or religious tradition in which the basic concept is to establish harmony with the Tao , which is the mechanism of everything that exists...

explicitly denies the fixity of biological species and Taoist philosophers speculated that species had developed differing attributes in response to differing environments. Taoism regards humans, nature and the heavens as existing in a state of "constant transformation" known as the Tao
Tao
Dao or Tao is a Chinese word meaning 'way', 'path', 'route', or sometimes more loosely, 'doctrine' or 'principle'...

, in contrast with the more static view of nature

Nature

Nature, in the broadest sense, is equivalent to the natural world, physical world, or material world. "Nature" refers to the phenomena of the physical world, and also to life in general...

typical of Western thought.

Romans

Titus Lucretius

Lucretius

Titus Lucretius Carus was a Roman poet and philosopher. His only known work is an epic philosophical poem laying out the beliefs of Epicureanism, De rerum natura, translated into English as On the Nature of Things or "On the Nature of the Universe".Virtually no details have come down concerning...

Carus (d. 50 BC), the Roman philosopher and atomist, wrote the poem On the Nature of Things
On the Nature of Things
De rerum natura is a 1st century BC didactic poem by the Roman poet and philosopher Lucretius with the goal of explaining Epicurean philosophy to a Roman audience. The poem, written in some 7,400 dactylic hexameters, is divided into six untitled books, and explores Epicurean physics through richly...

(De rerum natura), which provides the best surviving explanation of the ideas of the Greek Epicurean philosophers. It describes the development of the cosmos, the Earth, living things, and human society through purely naturalistic mechanisms, without any reference to supernatural involvement. On the Nature of things would influence the cosmological and evolutionary speculations of philosophers and scientists during and after the Renaissance

Renaissance

The Renaissance was a cultural movement that spanned roughly the 14th to the 17th century, beginning in Italy in the Late Middle Ages and later spreading to the rest of Europe. The term is also used more loosely to refer to the historical era, but since the changes of the Renaissance were not...

. This view was in strong contrast with the views of Roman philosophers of the stoic school such as Marcus Tullius Cicero, Seneca

Seneca the Younger

Lucius Annaeus Seneca was a Roman Stoic philosopher, statesman, dramatist, and in one work humorist, of the Silver Age of Latin literature. He was tutor and later advisor to emperor Nero...

, and Pliny the Elder

Pliny the Elder

Gaius Plinius Secundus , better known as Pliny the Elder, was a Roman author, naturalist, and natural philosopher, as well as naval and army commander of the early Roman Empire, and personal friend of the emperor Vespasian...

who had a strongly teleological view of the natural world that influenced Christian theology. Cicero reports that the peripatetic and stoic view of nature as an agency concerned most basically with producing life "best fitted for survival" was taken for granted among the Hellenistic elite.

Augustine of Hippo

In line with earlier Greek thought, the 4th century bishop and theologian, Augustine of Hippo

Augustine of Hippo

Augustine of Hippo , also known as Augustine, St. Augustine, St. Austin, St. Augoustinos, Blessed Augustine, or St. Augustine the Blessed, was Bishop of Hippo Regius . He was a Latin-speaking philosopher and theologian who lived in the Roman Africa Province...

, wrote that the creation story in Genesis should not be read too literally. In his book De Genesi ad litteram ("On The Literal Interpretation of Genesis"), he stated that in some cases new creatures may have come about through the "decomposition" of earlier forms of life. For Augustine, "plant, fowl and animal life are not perfect ... but created in a state of potentiality", unlike what he considered the theologically perfect forms of angels, the firmament

Firmament

The firmament is the vault or expanse of the sky. According to Genesis, God created the firmament to separate the oceans from other waters above.-Etymology:...

and the human soul

Soul

A soul in certain spiritual, philosophical, and psychological traditions is the incorporeal essence of a person or living thing or object. Many philosophical and spiritual systems teach that humans have souls, and others teach that all living things and even inanimate objects have souls. The...

. Augustine's idea 'that forms of life had been transformed "slowly over time"' prompted Father Giuseppe Tanzella-Nitti, Professor of Theology at the Pontifical Santa Croce University

Pontifical University of the Holy Cross

Pontifical University of the Holy Cross is a Roman Catholic university under the Curial Congregation for Catholic Education, which it has entrusted to the Prelature of the Holy Cross and Opus Dei, or more commonly called Opus Dei...

in Rome, to claim that Augustine had suggested a form of evolution.

Islamic philosophy and the struggle for existence

Although Greek and Roman evolutionary ideas died out in Europe after the fall of the Roman Empire

Roman Empire

The Roman Empire was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean....

, they were not lost to Islamic philosophers

Islamic philosophy

Islamic philosophy is a branch of Islamic studies. It is the continuous search for Hekma in the light of Islamic view of life, universe, ethics, society, and so on...

and scientists. In the Islamic Golden Age

Islamic Golden Age

During the Islamic Golden Age philosophers, scientists and engineers of the Islamic world contributed enormously to technology and culture, both by preserving earlier traditions and by adding their own inventions and innovations...

of the 8th to the 13th centuries, philosophers explored ideas about natural history

Natural history

Natural history is the scientific research of plants or animals, leaning more towards observational rather than experimental methods of study, and encompasses more research published in magazines than in academic journals. Grouped among the natural sciences, natural history is the systematic study...

. These ideas included transmutation from non-living to living: "from mineral to plant, from plant to animal, and from animal to man".

The first Muslim biologist and philosopher to publish detailed speculations about natural history, the Afro-Arab

Afro-Arab

Afro-Arab refers to people of mixed Black African and genealogical Arab ancestral heritage and/or linguistically and culturally Arabized Black Africans...

writer al-Jahiz

Al-Jahiz

Al-Jāḥiẓ was an Arabic prose writer and author of works of literature, Mu'tazili theology, and politico-religious polemics.In biology, Al-Jahiz introduced the concept of food chains and also proposed a scheme of animal evolution that entailed...

, wrote in the 9th century. In the Book of Animals, he considered the effects of the environment on an animal's chances for survival, and described the struggle for existence. Al-Jahiz also wrote descriptions of food chain

Food chain

A food web depicts feeding connections in an ecological community. Ecologists can broadly lump all life forms into one of two categories called trophic levels: 1) the autotrophs, and 2) the heterotrophs...

s. Al-Jahiz speculated on the influence of the environment

Natural environment

The natural environment encompasses all living and non-living things occurring naturally on Earth or some region thereof. It is an environment that encompasses the interaction of all living species....

on animal

Animal

Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...

s and considered the effects of the environment on the likelihood of an animal to survive. For example, Al-Jahiz's wrote in his Book of Animals: "All animals, in short, can not exist without food, neither can the hunting animal escape being hunted in his turn. Every weak animal devours those weaker than itself. Strong animals cannot escape being devoured by other animals stronger than they".

Some of Ibn Khaldun

Ibn Khaldun

Ibn Khaldūn or Ibn Khaldoun was an Arab Tunisian historiographer and historian who is often viewed as one of the forerunners of modern historiography, sociology and economics...

's thoughts, according to some commentators, anticipate the biological

Biology

Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...

theory of evolution

Evolution

. In 1377 Ibn Khaldun wrote the Muqaddimah
Muqaddimah
The Muqaddimah , also known as the Muqaddimah of Ibn Khaldun or the Prolegomena , is a book written by the Maghrebian Muslim historian Ibn Khaldun in 1377 which records an early view of universal history...

in which he asserted that humans developed from "the world of the monkeys", in a process by which "species become more numerous" In chapter 1 he writes: "This world with all the created things in it has a certain order and solid construction. It shows nexuses between causes and things caused, combinations of some parts of creation with others, and transformations of some existent things into others, in a pattern that is both remarkable and endless."

The Muqaddimah also states in Chapter 6:

Christian philosophy and the great chain of being

During the Early Middle Ages

Early Middle Ages

The Early Middle Ages was the period of European history lasting from the 5th century to approximately 1000. The Early Middle Ages followed the decline of the Western Roman Empire and preceded the High Middle Ages...

, Greek classical learning was all but lost to the West. However, contact with the Islamic world

Islamic Golden Age

, where Greek manuscripts were preserved and expanded, soon led to a massive spate of Latin translations in the 12th century. Europeans were re-introduced to the works of Plato and Aristotle, as well as to Islamic thought

Early Islamic philosophy

Early Islamic philosophy or classical Islamic philosophy is a period of intense philosophical development beginning in the 2nd century AH of the Islamic calendar and lasting until the 6th century AH...

. Christian thinkers

Christian philosophy

Christian philosophy may refer to any development in philosophy that is characterised by coming from a Christian tradition.- Origins of Christian philosophy :...

of the scholastic

Scholasticism

school, in particular Abelard and Thomas Aquinas

Thomas Aquinas

Thomas Aquinas, O.P. , also Thomas of Aquin or Aquino, was an Italian Dominican priest of the Catholic Church, and an immensely influential philosopher and theologian in the tradition of scholasticism, known as Doctor Angelicus, Doctor Communis, or Doctor Universalis...

, combined Aristotelian classification with Plato's ideas of the goodness of God, and of all potential life forms being present in a perfect creation, to organize all inanimate, animate, and spiritual beings into a huge interconnected system: the scala naturæ, or great chain of being

Great chain of being

The great chain of being , is a Christian concept detailing a strict, religious hierarchical structure of all matter and life, believed to have been decreed by the Christian God.-Divisions:...

.

Within this system, everything that existed could be placed in order, from "lowest" to "highest", with Hell

Hell

In many religious traditions, a hell is a place of suffering and punishment in the afterlife. Religions with a linear divine history often depict hells as endless. Religions with a cyclic history often depict a hell as an intermediary period between incarnations...

at the bottom and God at the top—below God, an angelic hierarchy marked by the orbits of the planets, mankind in an intermediate position, and worms the lowest of the animals. As the universe was ultimately perfect, the great chain was also perfect. There were no empty links in the chain, and no link was represented by more than one species. Therefore no species could ever move from one position to another. Thus, in this Christianized version of Plato's perfect universe, species could never change, but remained forever fixed, in accordance with the text of Genesis. For humans to forget their position was seen as sinful, whether they behaved like lower animals or aspired to a higher station than was given them by their Creator.

Creatures on adjacent steps were expected to closely resemble each other, an idea expressed in the saying: ("nature does not make leaps"). This basic concept of the great chain of being greatly influenced the thinking of Western civilization

Western culture

Western culture, sometimes equated with Western civilization or European civilization, refers to cultures of European origin and is used very broadly to refer to a heritage of social norms, ethical values, traditional customs, religious beliefs, political systems, and specific artifacts and...

for centuries (and still has an influence today). It formed a part of the argument from design

Teleological argument

A teleological or design argument is an a posteriori argument for the existence of God based on apparent design and purpose in the universe. The argument is based on an interpretation of teleology wherein purpose and intelligent design appear to exist in nature beyond the scope of any such human...

presented by natural theology

Natural theology

. As a classification system, it became the major organizing principle and foundation of the emerging science of biology

Biology

in the 17th and 18th centuries.

Thomas Aquinas on creation and natural processes

While the development of the great chain of being and the argument from design by Christian theologians contributed to the view that the natural world fit into an unchanging designed hierarchy, some theologians were more open to the possibility that the world might have developed through natural processes. Thomas Aquinas

Thomas Aquinas

went even farther than Augustine of Hippo in arguing that scriptural texts like Genesis should not be interpreted in a literal way that conflicted with or constrained what natural philosophers learned about the workings of the natural world. He felt that the autonomy of nature was a sign of God's goodness and that there was no conflict between the concept of a divinely created universe, and the idea that the universe may have evolved over time through natural mechanisms. However, Aquinas disputed the views of those like the ancient Greek philosopher Empedocles who held that such natural processes showed that the universe could have developed without an underlying purpose. Rather holding that: "Hence, it is clear that nature is nothing but a certain kind of art, i.e., the divine art, impressed upon things, by which these things are moved to a determinate end. It is as if the shipbuilder were able to give to timbers that by which they would move themselves to take the form of a ship."

Renaissance and Enlightenment

In the first half of the 17th century, René Descartes

René Descartes

René Descartes ; was a French philosopher and writer who spent most of his adult life in the Dutch Republic. He has been dubbed the 'Father of Modern Philosophy', and much subsequent Western philosophy is a response to his writings, which are studied closely to this day...

's mechanical philosophy

Mechanism (philosophy)

Mechanism is the belief that natural wholes are like machines or artifacts, composed of parts lacking any intrinsic relationship to each other, and with their order imposed from without. Thus, the source of an apparent thing's activities is not the whole itself, but its parts or an external...

encouraged the use of the metaphor of the universe as a machine, a concept that would come to characterise the scientific revolution

Scientific revolution

The Scientific Revolution is an era associated primarily with the 16th and 17th centuries during which new ideas and knowledge in physics, astronomy, biology, medicine and chemistry transformed medieval and ancient views of nature and laid the foundations for modern science...

. Between 1650 and 1800 some evolutionists

Evolutionism

Evolutionism refers to the biological concept of evolution, specifically to a widely held 19th century belief that organisms are intrinsically bound to increase in complexity. The belief was extended to include cultural evolution and social evolution...

, such as Benoît de Maillet

Benoît de Maillet

Benoît de Maillet was a well-travelled French diplomat and natural historian. He was French consul general at Cairo, and overseer in the Levant...

, produced theories that maintained that the universe, the earth, and life, had developed mechanically, without divine guidance. In contrast, most contemporary theories of evolution, such of those of Gottfried Leibniz

Gottfried Leibniz

Gottfried Wilhelm Leibniz was a German philosopher and mathematician. He wrote in different languages, primarily in Latin , French and German ....

and J. G. Herder, regarded evolution as a fundamentally spiritual process. In 1751, Pierre Louis Maupertuis

Pierre Louis Maupertuis

Pierre-Louis Moreau de Maupertuis was a French mathematician, philosopher and man of letters. He became the Director of the Académie des Sciences, and the first President of the Berlin Academy of Science, at the invitation of Frederick the Great....

veered toward more materialist

Materialism

In philosophy, the theory of materialism holds that the only thing that exists is matter; that all things are composed of material and all phenomena are the result of material interactions. In other words, matter is the only substance...

ground. He wrote of natural modifications occurring during reproduction and accumulating over the course of many generations, producing races and even new species, a description that anticipated in general terms the concept of natural selection.

Maupertuis's ideas were in opposition to the influence of early taxonomists like John Ray

John Ray

John Ray was an English naturalist, sometimes referred to as the father of English natural history. Until 1670, he wrote his name as John Wray. From then on, he used 'Ray', after "having ascertained that such had been the practice of his family before him".He published important works on botany,...

. In the late 17th century Ray had given the first formal definition of a biological species, which he described as being characterized by essential unchanging features, and stated the seed of one species could never give rise to another. The ideas of Ray and other 17th century taxonomists were influenced by natural theology

Natural theology

and the argument from design.

The word evolution (from the Latin

Latin

evolutio, meaning "to unroll like a scroll") was initially used to refer to embryological development; its first use in relation to development of species came in 1762, when Charles Bonnet

Charles Bonnet

Charles Bonnet , Swiss naturalist and philosophical writer, was born at Geneva, of a French family driven into Switzerland by the religious persecution in the 16th century.-Life and work:Bonnet's life was uneventful...

used it for his concept of "pre-formation

Preformationism

In the history of biology, preformationism is either the specific contention that all organisms were created at the same time, and that succeeding generations grow from homunculi, animalcules, or other fully formed but miniature versions of themselves that have existed since the beginning of...

", in which females carried a miniature form

Homunculus

Homunculus is a term used, generally, in various fields of study to refer to any representation of a human being. Historically, it referred specifically to the concept of a miniature though fully formed human body, for example, in the studies of alchemy and preformationism...

of all future generations. The term gradually gained a more general meaning of growth or progressive development.

Later in the 18th century, the French philosopher G. L. L. Buffon

Georges-Louis Leclerc, Comte de Buffon

Georges-Louis Leclerc, Comte de Buffon was a French naturalist, mathematician, cosmologist, and encyclopedic author.His works influenced the next two generations of naturalists, including Jean-Baptiste Lamarck and Georges Cuvier...

, one of the leading naturalist

Naturalist

Naturalist may refer to:* Practitioner of natural history* Conservationist* Advocate of naturalism * Naturalist , autobiography-See also:* The American Naturalist, periodical* Naturalism...

s of the time, suggested that what most people referred to as species were really just well-marked varieties, modified from an original form by environmental factors. For example, he believed that lions, tigers, leopards and house cats might all have a common ancestor. He further speculated that the 200 or so species of mammals then known might have descended from as few as 38 original animal forms. Buffon's evolutionary ideas were limited; he believed each of the original forms had arisen through spontaneous generation

Spontaneous generation

Spontaneous generation or Equivocal generation is an obsolete principle regarding the origin of life from inanimate matter, which held that this process was a commonplace and everyday occurrence, as distinguished from univocal generation, or reproduction from parent...

and that each was shaped by "internal moulds" that limited the amount of change. Buffon's works, Natural History and The Epochs of Nature, containing well developed theories about a completely materialistic origin for the Earth and his ideas questioning the fixity of species, were extremely influential. Another French philosopher, Denis Diderot

Denis Diderot

Denis Diderot was a French philosopher, art critic, and writer. He was a prominent person during the Enlightenment and is best known for serving as co-founder and chief editor of and contributor to the Encyclopédie....

, also wrote that living things might have first arisen through spontaneous generation, and that species were always changing through a constant process of experiment where new forms arose and survived or not based on trial and error; an idea that can be considered a partial anticipation of natural selection

Natural selection

. Between 1767 and 1792, James Burnett, Lord Monboddo

James Burnett, Lord Monboddo

James Burnett, Lord Monboddo was a Scottish judge, scholar of linguistic evolution, philosopher and deist. He is most famous today as a founder of modern comparative historical linguistics . In 1767 he became a judge in the Court of Session. As such, Burnett adopted an honorary title based on his...

included in his writings not only the concept that man had descended from primates, but also that, in response to the environment, creatures had found methods of transforming their characteristics over long time intervals. Charles Darwin's grandfather, Erasmus Darwin

Erasmus Darwin

Erasmus Darwin was an English physician who turned down George III's invitation to be a physician to the King. One of the key thinkers of the Midlands Enlightenment, he was also a natural philosopher, physiologist, slave trade abolitionist,inventor and poet...

, published Zoönomia
Zoönomia
Zoonomia; or the Laws of Organic Life is a two-volume medical work by Erasmus Darwin dealing with pathology, anatomy, psychology, and the functioning of the body...

in 1796, which suggested that "all warm-blooded animals have arisen from one living filament". In his 1802 poem Temple of Nature, he described the rise of life from minute organisms living in mud to all of its modern diversity.

Early 19th century

Paleontology and geology

In 1796 Georges Cuvier

Georges Cuvier

Georges Chrétien Léopold Dagobert Cuvier or Jean Léopold Nicolas Frédéric Cuvier , known as Georges Cuvier, was a French naturalist and zoologist...

published his findings on the differences between living elephant

Elephant

Elephants are large land mammals in two extant genera of the family Elephantidae: Elephas and Loxodonta, with the third genus Mammuthus extinct...

s and those found in the fossil

Fossil

Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

record. His analysis identified mammoth

Mammoth

A mammoth is any species of the extinct genus Mammuthus. These proboscideans are members of Elephantidae, the family of elephants and mammoths, and close relatives of modern elephants. They were often equipped with long curved tusks and, in northern species, a covering of long hair...

s and mastodon

Mastodon

Mastodons were large tusked mammal species of the extinct genus Mammut which inhabited Asia, Africa, Europe, North America and Central America from the Oligocene through Pleistocene, 33.9 mya to 11,000 years ago. The American mastodon is the most recent and best known species of the group...

s as distinct species, different from any living animal, and effectively ended a long-running debate over whether a species could go extinct. In 1788, James Hutton

James Hutton

James Hutton was a Scottish physician, geologist, naturalist, chemical manufacturer and experimental agriculturalist. He is considered the father of modern geology...

described gradual

Gradualism

Gradualism is the belief in or the policy of advancing toward a goal by gradual, often slow stages.-Politics and society:In politics, the concept of gradualism is used to describe the belief that change ought to be brought about in small, discrete increments rather than in abrupt strokes such as...

geological processes operating continuously over deep time

Deep time

Deep time is the concept that the Geologic time scale is vast because the Earth is very old. The modern philosophical concept was developed in the 18th century by Scottish geologist James Hutton...

. In the 1790s William Smith

William Smith (geologist)

William 'Strata' Smith was an English geologist, credited with creating the first nationwide geological map. He is known as the "Father of English Geology" for collating the geological history of England and Wales into a single record, although recognition was very slow in coming...

began the process of ordering rock strata

Stratum

In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...

by examining fossils in the layers while he worked on his geologic map of England

England

England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

. Independently, in 1811, Georges Cuvier and Alexandre Brongniart

Alexandre Brongniart

Alexandre Brongniart was a French chemist, mineralogist, and zoologist, who collaborated with Georges Cuvier on a study of the geology of the region around Paris...

published an influential study of the geologic history of the region around Paris, based on the stratigraphic

Stratigraphy

Stratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....

succession of rock layers. These works helped establish the antiquity of the Earth. Cuvier advocated catastrophism

Catastrophism

Catastrophism is the theory that the Earth has been affected in the past by sudden, short-lived, violent events, possibly worldwide in scope. The dominant paradigm of modern geology is uniformitarianism , in which slow incremental changes, such as erosion, create the Earth's appearance...

to explain the patterns of extinction and faunal succession revealed by the fossil record.

Knowledge of the fossil record continued to advance rapidly during the first few decades of the 19th century. By the 1840s, the outlines of the geologic timescale

Geologic time scale

The geologic time scale provides a system of chronologic measurement relating stratigraphy to time that is used by geologists, paleontologists and other earth scientists to describe the timing and relationships between events that have occurred during the history of the Earth...

were becoming clear, and in 1841 John Phillips

John Phillips (geologist)

John Phillips FRS was an English geologist.- Life and work :Philips was born at Marden in Wiltshire...

named three major eras, based on the predominant fauna

Fauna

Fauna or faunæ is all of the animal life of any particular region or time. The corresponding term for plants is flora.Zoologists and paleontologists use fauna to refer to a typical collection of animals found in a specific time or place, e.g. the "Sonoran Desert fauna" or the "Burgess shale fauna"...

of each: the Paleozoic

Paleozoic

The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...

, dominated by marine invertebrate

Invertebrate

An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...

s and fish, the Mesozoic

Mesozoic

The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...

, the age of reptiles, and the current Cenozoic

Cenozoic

The Cenozoic era is the current and most recent of the three Phanerozoic geological eras and covers the period from 65.5 mya to the present. The era began in the wake of the Cretaceous–Tertiary extinction event at the end of the Cretaceous that saw the demise of the last non-avian dinosaurs and...

age of mammals. This progressive picture of the history of life was accepted even by conservative English geologists like Adam Sedgwick

Adam Sedgwick

Adam Sedgwick was one of the founders of modern geology. He proposed the Devonian period of the geological timescale...

and William Buckland

William Buckland

The Very Rev. Dr William Buckland DD FRS was an English geologist, palaeontologist and Dean of Westminster, who wrote the first full account of a fossil dinosaur, which he named Megalosaurus...

; however, like Cuvier, they attributed the progression to repeated catastrophic episodes of extinction followed by new episodes of creation. Unlike Cuvier, Buckland and some other advocates of natural theology

Natural theology

among British geologists made efforts to explicitly link the last catastrophic episode proposed by Cuvier to the biblical flood

Noah's Ark

Noah's Ark is a vessel appearing in the Book of Genesis and the Quran . These narratives describe the construction of the ark by Noah at God's command to save himself, his family, and the world's animals from the worldwide deluge of the Great Flood.In the narrative of the ark, God sees the...

.

From 1830 to 1833, Charles Lyell

Charles Lyell

Sir Charles Lyell, 1st Baronet, Kt FRS was a British lawyer and the foremost geologist of his day. He is best known as the author of Principles of Geology, which popularised James Hutton's concepts of uniformitarianism – the idea that the earth was shaped by slow-moving forces still in operation...

published his multi-volume work Principles of Geology
Principles of Geology
Principles of Geology, being an attempt to explain the former changes of the Earth's surface, by reference to causes now in operation, is a book by the Scottish geologist Charles Lyell....

, which, building on Hutton's ideas, advocated a uniformitarian

Uniformitarianism (science)

In the philosophy of naturalism, the uniformitarianism assumption is that the same natural laws and processes that operate in the universe now, have always operated in the universe in the past and apply everywhere in the universe. It has included the gradualistic concept that "the present is the...

alternative to the catastrophic theory of geology. Lyell claimed that, rather than being the products of cataclysmic (and possibly supernatural) events, the geologic features of the Earth are better explained as the result of the same gradual geologic forces observable in the present day—but acting over immensely long periods of time. Although Lyell opposed evolutionary ideas (even questioning the consensus that the fossil record demonstrates a true progression), his concept that the Earth was shaped by forces working gradually over an extended period, and the immense age of the Earth assumed by his theories, would strongly influence future evolutionary thinkers such as Charles Darwin

Charles Darwin

Transmutation of species

Jean-Baptiste Lamarck

Jean-Baptiste Pierre Antoine de Monet, Chevalier de la Marck , often known simply as Lamarck, was a French naturalist...

proposed, in his Philosophie Zoologique
Philosophie Zoologique
Philosophie zoologique ou exposition des considérations relatives à l'histoire naturelle des animaux is an 1809 book by Jean-Baptiste Lamarck in which he outlines his theory of evolution now known as Lamarckism.Lamarck proposed that :“as new modifications will necessarily continue...

of 1809, a theory of the transmutation of species. Lamarck did not believe that all living things shared a common ancestor but rather that simple forms of life were created continuously by spontaneous generation

Abiogenesis

Abiogenesis or biopoesis is the study of how biological life arises from inorganic matter through natural processes, and the method by which life on Earth arose...

. He also believed that an innate life force drove species to become more complex over time, advancing up a linear ladder of complexity that was related to the great chain of being. Lamarck recognized that species were adapted to their environment. He explained this by saying that the same innate force driving increasing complexity caused the organs of an animal (or a plant) to change based on the use or disuse of those organs, just as muscles are affected by exercise. He argued that these changes would be inherited by the next generation and produce slow adaptation to the environment. It was this secondary mechanism of adaptation through the inheritance of acquired characteristics that would become known as Lamarckism

Lamarckism

Lamarckism is the idea that an organism can pass on characteristics that it acquired during its lifetime to its offspring . It is named after the French biologist Jean-Baptiste Lamarck , who incorporated the action of soft inheritance into his evolutionary theories...

and would influence discussions of evolution into the 20th century.

A radical British school of comparative anatomy that included the anatomist Robert Grant

Robert Edmond Grant

Robert Edmond Grant MD FRCPEd FRS was born in Edinburgh and educated at Edinburgh University as a physician. He became one of the foremost biologists of the early 19th century at Edinburgh and subsequently the first Professor of Comparative Anatomy at University College London...

was closely in touch with Lamarck's French school of Transformationism. One of the French scientists who influenced Grant was the anatomist Étienne Geoffroy Saint-Hilaire

Étienne Geoffroy Saint-Hilaire

Étienne Geoffroy Saint-Hilaire was a French naturalist who established the principle of "unity of composition". He was a colleague of Jean-Baptiste Lamarck and expanded and defended Lamarck's evolutionary theories...

, whose ideas on the unity of various animal body plans and the homology

Homology (biology)

Homology forms the basis of organization for comparative biology. In 1843, Richard Owen defined homology as "the same organ in different animals under every variety of form and function". Organs as different as a bat's wing, a seal's flipper, a cat's paw and a human hand have a common underlying...

of certain anatomical structures would be widely influential and lead to intense debate with his colleague Georges Cuvier

Georges Cuvier

Georges Chrétien Léopold Dagobert Cuvier or Jean Léopold Nicolas Frédéric Cuvier , known as Georges Cuvier, was a French naturalist and zoologist...

. Grant became an authority on the anatomy and reproduction of marine invertebrates. He developed Lamarck's and Erasmus Darwin

Erasmus Darwin

's ideas of transmutation

Transmutation of species

and evolutionism

Evolutionism

, and investigated homology, even proposing that plants and animals had a common evolutionary starting point. As a young student Charles Darwin joined Grant in investigations of the life cycle of marine animals. In 1826 an anonymous paper, probably written by Robert Jameson

Robert Jameson

thumb|Robert JamesonProfessor Robert Jameson, FRS FRSE was a Scottish naturalist and mineralogist.As Regius Professor at the University of Edinburgh for fifty years, Jameson is notable for his advanced scholarship in natural history, his superb museum collection, and for his tuition of Charles...

, praised Lamarck for explaining how higher animals had "evolved" from the simplest worms; this was the first use of the word "evolved" in a modern sense.

In 1844, the Scottish publisher Robert Chambers anonymously published an extremely controversial but widely read book entitled Vestiges of the Natural History of Creation
Vestiges of the Natural History of Creation
Vestiges of the Natural History of Creation is a unique work of speculative natural history published anonymously in England in 1844. It brought together various ideas of stellar evolution with the progressive transmutation of species in an accessible narrative which tied together numerous...

. This book proposed an evolutionary scenario for the origins of the Solar System and life on Earth. It claimed that the fossil record showed a progressive ascent of animals with current animals being branches off a main line that leads progressively to humanity. It implied that the transmutations lead to the unfolding of a preordained plan that had been woven into the laws that governed the universe. In this sense it was less completely materialistic than the ideas of radicals like Robert Grant, but its implication that humans were only the last step in the ascent of animal life incensed many conservative thinkers. The high profile of the public debate over Vestiges, with its depiction of evolution as a progressive process, would greatly influence the perception of Darwin's theory a decade later.

Ideas about the transmutation of species were associated with the radical materialism of the Enlightenment

Age of Enlightenment

and were attacked by more conservative thinkers. Georges Cuvier

Georges Cuvier

Georges Chrétien Léopold Dagobert Cuvier or Jean Léopold Nicolas Frédéric Cuvier , known as Georges Cuvier, was a French naturalist and zoologist...

attacked the ideas of Lamarck and Geoffroy Saint-Hilaire, agreeing with Aristotle that species were immutable. Cuvier believed that the individual parts of an animal were too closely correlated with one another to allow for one part of the anatomy to change in isolation from the others, and argued that the fossil record showed patterns of catastrophic extinctions followed by re-population, rather than gradual change over time. He also noted that drawings of animals and animal mummies from Egypt, which were thousands of years old, showed no signs of change when compared with modern animals. The strength of Cuvier's arguments and his scientific reputation helped keep transmutational ideas out of the mainstream for decades.

In Britain the philosophy of natural theology

Natural theology

remained influential. William Paley

William Paley

William Paley was a British Christian apologist, philosopher, and utilitarian. He is best known for his exposition of the teleological argument for the existence of God in his work Natural Theology, which made use of the watchmaker analogy .-Life:Paley was Born in Peterborough, England, and was...

's 1802 book Natural Theology with its famous watchmaker analogy

Watchmaker analogy

The watchmaker analogy, or watchmaker argument, is a teleological argument for the existence of God. By way of an analogy, the argument states that design implies a designer...

had been written at least in part as a response to the transmutational ideas of Erasmus Darwin

Erasmus Darwin

. Geologists influenced by natural theology, such as Buckland and Sedgwick, made a regular practice of attacking the evolutionary ideas of Lamarck, Grant, and The Vestiges of the Natural History of Creation. Although the geologist Charles Lyell

Charles Lyell

opposed scriptural geology, he also believed in the immutability of species, and in his Principles of Geology (1830–1833), he criticized Lamarck's theories of development. Idealists such as Louis Agassiz

Louis Agassiz

Jean Louis Rodolphe Agassiz was a Swiss paleontologist, glaciologist, geologist and a prominent innovator in the study of the Earth's natural history. He grew up in Switzerland and became a professor of natural history at University of Neuchâtel...

and Richard Owen

Richard Owen

Sir Richard Owen, FRS KCB was an English biologist, comparative anatomist and palaeontologist.Owen is probably best remembered today for coining the word Dinosauria and for his outspoken opposition to Charles Darwin's theory of evolution by natural selection...

believed that each species was fixed and unchangeable because it represented an idea in the mind of the creator. They believed that relationships between species could be discerned from developmental patterns in embryology

Embryology

Embryology is a science which is about the development of an embryo from the fertilization of the ovum to the fetus stage...

, as well as in the fossil record, but that these relationships represented an underlying pattern of divine thought, with progressive creation leading to increasing complexity and culminating in humanity. Owen developed the idea of "archetypes" in the Divine mind that would produce a sequence of species related by anatomical homologies

Homology (biology)

, such as vertebrate

Vertebrate

Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...

limbs. Owen led a public campaign that successfully marginalized Robert Grant in the scientific community. Darwin would make good use of the homologies analyzed by Owen in his own theory, but the harsh treatment of Grant, and the controversy surrounding Vestiges, showed him the need to ensure that his own ideas were scientifically sound.

Anticipations of natural selection

Several writers anticipated aspects of Darwin's theory, and in the third edition of On the Origin of Species published in 1861 Darwin named those he knew about in an introductory appendix, An Historical Sketch of the Recent Progress of Opinion on the Origin of Species, which he expanded in later editions.

In 1813, William Charles Wells

William Charles Wells

William Charles Wells MD FRS FRSEd , was a Scottish-American physician and printer. He lived a life of extraordinary variety, did some notable medical research, and made the first clear statement about natural selection. He applied the idea to the origin of different skin colours in human races,...

read before the Royal Society

Royal Society

The Royal Society of London for Improving Natural Knowledge, known simply as the Royal Society, is a learned society for science, and is possibly the oldest such society in existence. Founded in November 1660, it was granted a Royal Charter by King Charles II as the "Royal Society of London"...

essays assuming that there had been evolution of humans, and recognising the principle of natural selection

Natural selection

. Charles Darwin and Alfred Russel Wallace were unaware of this work when they jointly published the theory in 1858, but Darwin later acknowledged that Wells had recognised the principle before them, writing that the paper "An Account of a White Female, part of whose Skin resembles that of a Negro" was published in 1818, and "he distinctly recognises the principle of natural selection, and this is the first recognition which has been indicated; but he applies it only to the races of man, and to certain characters alone." When Darwin was developing his theory, he was influenced by Augustin de Candolle

A. P. de Candolle

Augustin Pyramus de Candolle also spelled Augustin Pyrame de Candolle was a Swiss botanist. René Louiche Desfontaines launched Candolle's botanical career by recommending him at an herbarium...

's natural system of classification, which laid emphasis on the war between competing species.

Patrick Matthew

Patrick Matthew

Patrick Matthew was a Scottish landowner and fruit farmer. He published the principle of natural selection as a mechanism of evolution over a quarter-century earlier than Charles Darwin and Alfred Russel Wallace...

wrote in the obscure book Naval Timber & Arboriculture (1831) of "continual balancing of life to circumstance. ... [The] progeny of the same parents, under great differences of circumstance, might, in several generations, even become distinct species, incapable of co-reproduction." Charles Darwin discovered this work after the initial publication of the Origin. In the brief historical sketch that Darwin included in the 3rd edition he says "Unfortunately the view was given by Mr. Matthew very briefly in an Appendix to a work on a different subject ... He clearly saw, however, the full force of the principle of natural selection."

It is possible to look through the history of biology from the ancient Greeks onwards and discover anticipations of almost all of Darwin's key ideas. However, as historian of science Peter J. Bowler

Peter J. Bowler

Peter J. Bowler is a historian of biology who has written extensively on the history of evolutionary thought, the history of the environmental sciences, and on the history of genetics. His 1984 book, Evolution: The History of an Idea is a standard textbook on the history of evolution, and was...

says, "Through a combination of bold theorizing and comprehensive evaluation, Darwin came up with a concept of evolution that was unique for the time." Bowler goes on to say that simple priority alone is not enough to secure a place in the history of science; someone has to develop an idea and convince others of its importance to have a real impact.

T. H. Huxley said in his essay on the reception of the Origin of Species:

The suggestion that new species may result from the selective action of external conditions upon the variations from their specific type which individuals present and which we call spontaneous because we are ignorant of their causation is as wholly unknown to the historian of scientific ideas as it was to biological specialists before 1858. But that suggestion is the central idea of the Origin of Species, and contains the quintessence of Darwinism
Darwinism
Darwinism is a set of movements and concepts related to ideas of transmutation of species or of evolution, including some ideas with no connection to the work of Charles Darwin....

.

Natural selection

The biogeographical

Biogeography

patterns Charles Darwin observed in places such as the Galapagos islands

Galápagos Islands

The Galápagos Islands are an archipelago of volcanic islands distributed around the equator in the Pacific Ocean, west of continental Ecuador, of which they are a part.The Galápagos Islands and its surrounding waters form an Ecuadorian province, a national park, and a...

during the voyage of the Beagle

Second voyage of HMS Beagle

The second voyage of HMS Beagle, from 27 December 1831 to 2 October 1836, was the second survey expedition of HMS Beagle, under captain Robert FitzRoy who had taken over command of the ship on its first voyage after her previous captain committed suicide...

caused him to doubt the fixity of species, and in 1837 Darwin started the first of a series of secret notebooks on transmutation

Transmutation of species

. Darwin's observations led him to view transmutation as a process of divergence and branching, rather than the ladder-like progression envisioned by Lamarck and others. In 1838 he read the new 6th edition of An Essay on the Principle of Population
An Essay on the Principle of Population
The book An Essay on the Principle of Population was first published anonymously in 1798 through J. Johnson . The author was soon identified as The Reverend Thomas Robert Malthus. While it was not the first book on population, it has been acknowledged as the most influential work of its era...

, written in the late 18th century by Thomas Malthus

Thomas Malthus

The Reverend Thomas Robert Malthus FRS was an English scholar, influential in political economy and demography. Malthus popularized the economic theory of rent....

. Malthus' idea of population growth leading to a struggle for survival combined with Darwin's knowledge on how breeders selected traits, led to the inception of Darwin's theory

Inception of Darwin's theory

The inception of Darwin's theory occurred during an intensively busy period which began when Charles Darwin returned from the survey voyage of the Beagle, with his reputation as a fossil collector and geologist already established...

of natural selection

Natural selection

. Darwin did not publish his ideas on evolution for 20 years. However he did share them with certain other naturalists and friends, starting with Joseph Hooker

Joseph Dalton Hooker

Sir Joseph Dalton Hooker OM, GCSI, CB, MD, FRS was one of the greatest British botanists and explorers of the 19th century. Hooker was a founder of geographical botany, and Charles Darwin's closest friend...

, with whom he discussed his unpublished 1844 essay on natural selection. During this period he used the time he could spare from his other scientific work to slowly refine his ideas and, aware of the intense controversy around transmutation, amass evidence to support them. In September 1854 he began full time work on writing his book on natural selection.

Unlike Darwin, Alfred Russel Wallace

Alfred Russel Wallace

Alfred Russel Wallace, OM, FRS was a British naturalist, explorer, geographer, anthropologist and biologist...

, influenced by the book Vestiges of the Natural History of Creation
Vestiges of the Natural History of Creation
Vestiges of the Natural History of Creation is a unique work of speculative natural history published anonymously in England in 1844. It brought together various ideas of stellar evolution with the progressive transmutation of species in an accessible narrative which tied together numerous...

, already suspected that transmutation of species occurred when he began his career as a naturalist. By 1855 his biogeographical observations during his field work in South America

South America

South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...

and the Malay Archipelago

Malay Archipelago

The Malay Archipelago refers to the archipelago between mainland Southeastern Asia and Australia. The name was derived from the anachronistic concept of a Malay race....

made him confident enough in a branching pattern of evolution to publish a paper stating that every species originated in close proximity to an already existing closely allied species. Like Darwin, it was Wallace's consideration of how the ideas of Malthus might apply to animal populations that led him to conclusions very similar to those reached by Darwin about the role of natural selection. In February 1858 Wallace, unaware of Darwin's unpublished ideas, composed his thoughts into an essay and mailed them to Darwin, asking for his opinion. The result was the joint publication in July of an extract from Darwin's 1844 essay along with Wallace's letter. Darwin also began work on a short abstract summarising his theory, which he would publish in 1859 as On the Origin of Species.

1859–1930s: Darwin and his legacy

By the 1850s, whether or not species evolved was a subject of intense debate, with prominent scientists arguing both sides of the issue. The publication of Charles Darwin

Charles Darwin

's On the Origin of Species (1859) fundamentally transformed the discussion over biological origins. Darwin argued that his branching version of evolution explained a wealth of facts in biogeography, anatomy, embryology, and other fields of biology. He also provided the first cogent mechanism by which evolutionary change could persist: his theory of natural selection

Natural selection

.

One of the first and most important naturalists to be convinced by Origin of the reality of evolution was the British anatomist Thomas Henry Huxley. Huxley recognized that unlike the earlier transmutational ideas of Lamarck and Vestiges, Darwin's theory provided a mechanism for evolution without supernatural involvement, even if Huxley himself was not completely convinced that natural selection was the key evolutionary mechanism. Huxley would make advocacy of evolution a cornerstone of the program of the X Club

X Club

The X Club was a dining club of nine men who supported the theories of natural selection and academic liberalism in late 19th-century England. Thomas Henry Huxley was the initiator: he called the first meeting for November 3, 1864...

to reform and professionalise science by displacing natural theology

Natural theology

with naturalism

Naturalism (philosophy)

Naturalism commonly refers to the philosophical viewpoint that the natural universe and its natural laws and forces operate in the universe, and that nothing exists beyond the natural universe or, if it does, it does not affect the natural universe that we know...

and to end the domination of British natural science by the clergy. By the early 1870s in English-speaking countries, thanks partly to these efforts, evolution had become the mainstream scientific explanation for the origin of species. In his campaign for public and scientific acceptance of Darwin's theory, Huxley made extensive use of new evidence for evolution from paleontology. This included evidence that birds had evolved from reptiles, including the discovery of Archaeopteryx
Archaeopteryx
Archaeopteryx , sometimes referred to by its German name Urvogel , is a genus of theropod dinosaur that is closely related to birds. The name derives from the Ancient Greek meaning "ancient", and , meaning "feather" or "wing"...

in Europe, and a number of fossils of primitive birds with teeth found in North America. Another important line of evidence was the finding of fossils that helped trace the evolution of the horse

Evolution of the horse

The evolution of the horse pertains to the phylogenetic ancestry of the modern horse from the small dog-sized, forest-dwelling Hyracotherium over geologic time scales...

from its small five-toed ancestors. However, acceptance of evolution among scientists in non-English speaking nations such as France, and the countries of southern Europe and Latin America was slower. An exception to this was Germany, where both August Weismann

August Weismann

Friedrich Leopold August Weismann was a German evolutionary biologist. Ernst Mayr ranked him the second most notable evolutionary theorist of the 19th century, after Charles Darwin...

and Ernst Haeckel

Ernst Haeckel

The "European War" became known as "The Great War", and it was not until 1920, in the book "The First World War 1914-1918" by Charles à Court Repington, that the term "First World War" was used as the official name for the conflict.-Research:...

championed this idea: Haeckel used evolution to challenge the established tradition of metaphysical idealism in German biology, much as Huxley used it to challenge natural theology in Britain. Haeckel and other German scientists would take the lead in launching an ambitious programme to reconstruct the evolutionary history of life based on morphology

Morphology (biology)

In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....

and embryology

Embryology

Embryology is a science which is about the development of an embryo from the fertilization of the ovum to the fetus stage...

.

Darwin's theory succeeded in profoundly altering scientific opinion regarding the development of life and in producing a small philosophical revolution. However, this theory could not explain several critical components of the evolutionary process. Specifically, Darwin was unable to explain the source of variation in traits within a species, and could not identify a mechanism that could pass traits faithfully from one generation to the next. Darwin's hypothesis of pangenesis

Pangenesis

Pangenesis was Charles Darwin's hypothetical mechanism for heredity. He presented this 'provisional hypothesis' in his 1868 work The Variation of Animals and Plants under Domestication and felt that it brought 'together a multitude of facts which are at present left disconnected by any efficient...

, while relying in part on the inheritance of acquired characteristics

Inheritance of acquired characters

The inheritance of acquired characteristics is a hypothesis that physiological changes acquired over the life of an organism may be transmitted to offspring...

, proved to be useful for statistical models of evolution that were developed by his cousin Francis Galton

Francis Galton

Sir Francis Galton /ˈfrɑːnsɪs ˈgɔːltn̩/ FRS , cousin of Douglas Strutt Galton, half-cousin of Charles Darwin, was an English Victorian polymath: anthropologist, eugenicist, tropical explorer, geographer, inventor, meteorologist, proto-geneticist, psychometrician, and statistician...

and the "biometric" school of evolutionary thought. However, this idea proved to be of little use to other biologists.

Application to humans

Charles Darwin was aware of the severe reaction in some parts of the scientific community against the suggestion made in Vestiges of the Natural History of Creation that humans had arisen from animals by a process of transmutation. Therefore he almost completely ignored the topic of human evolution

Human evolution

Human evolution refers to the evolutionary history of the genus Homo, including the emergence of Homo sapiens as a distinct species and as a unique category of hominids and mammals...

in The Origin of Species. Despite this precaution, the issue featured prominently in the debate that followed the book's publication. For most of the first half of the 19th century, the scientific community believed that, although geology had shown that the Earth and life were very old, human beings had appeared suddenly just a few thousand years before the present. However, a series of archaeological discoveries in the 1840s and 1850s showed stone tools associated with the remains of extinct animals. By the early 1860s, as summarized in Charles Lyell

Charles Lyell

's 1863 book Geological Evidences of the Antiquity of Man, it had become widely accepted that humans had existed during a prehistoric period – which stretched many thousands of years before the start of written history. This view of human history was more compatible with an evolutionary origin for humanity than was the older view. On the other hand, at that time there was no fossil evidence to demonstrate human evolution. The only human fossils found before the discovery of Java man

Java Man

Java Man is the name given to fossils discovered in 1891 at Trinil - Ngawi Regency on the banks of the Solo River in East Java, Indonesia, one of the first known specimens of Homo erectus...

in the 1890s were either of anatomically modern humans or of Neanderthal

Neanderthal

The Neanderthal is an extinct member of the Homo genus known from Pleistocene specimens found in Europe and parts of western and central Asia...

s that were too close, especially in the critical characteristic of cranial capacity, to modern humans for them to be convincing intermediates between humans and other primates.

Therefore the debate that immediately followed the publication of The Origin of Species centered on the similarities and differences between humans and modern ape

Ape

Apes are Old World anthropoid mammals, more specifically a clade of tailless catarrhine primates, belonging to the biological superfamily Hominoidea. The apes are native to Africa and South-east Asia, although in relatively recent times humans have spread all over the world...

s. Carolus Linnaeus had been criticised in the 18th century for grouping humans and apes together as primates in his ground breaking classification system. Richard Owen

Richard Owen

vigorously defended the classification suggested by Cuvier and Johann Friedrich Blumenbach

Johann Friedrich Blumenbach

Johann Friedrich Blumenbach was a German physician, physiologist and anthropologist, one of the first to explore the study of mankind as an aspect of natural history, whose teachings in comparative anatomy were applied to classification of what he called human races, of which he determined...

that placed humans in a separate order from any of the other mammals, which by the early 19th century had become the orthodox view. On the other hand, Thomas Henry Huxley sought to demonstrate a close anatomical relationship between humans and apes. In one famous incident, which became known as the Great Hippocampus Question

Great Hippocampus Question

The Great Hippocampus Question was a 19th century scientific controversy about the anatomy of apes and human uniqueness. The dispute between Thomas Henry Huxley and Richard Owen became central to the scientific debate on human evolution that followed Charles Darwin's publication of On the Origin of...

, Huxley showed that Owen was mistaken in claiming that the brains of gorilla

Gorilla

Gorillas are the largest extant species of primates. They are ground-dwelling, predominantly herbivorous apes that inhabit the forests of central Africa. Gorillas are divided into two species and either four or five subspecies...

s lacked a structure present in human brains. Huxley summarized his argument in his highly influential 1863 book Evidence as to Man's Place in Nature
Evidence as to Man's Place in Nature
Evidence as to Man's Place in Nature is an 1863 book by Thomas Henry Huxley, in which he gives evidence for the evolution of man and apes from a common ancestor. It was the first book devoted to the topic of human evolution, and discussed much of the anatomical and other evidence...

. Another viewpoint was advocated by Charles Lyell and Alfred Russel Wallace

Alfred Russel Wallace

Alfred Russel Wallace, OM, FRS was a British naturalist, explorer, geographer, anthropologist and biologist...

. They agreed that humans shared a common ancestor with apes, but questioned whether any purely materialistic mechanism could account for all the differences between humans and apes, especially some aspects of the human mind.

In 1871, Darwin published The Descent of Man, and Selection in Relation to Sex
The Descent of Man, and Selection in Relation to Sex
The Descent of Man, and Selection in Relation to Sex is a book on evolutionary theory by English naturalist Charles Darwin, first published in 1871. It was Darwin's second great book on evolutionary theory, following his 1859 work, On The Origin of Species. In The Descent of Man, Darwin applies...

, which contained his views on human evolution. Darwin argued that the differences between the human mind and the minds of the higher animals were a matter of degree rather than of kind. For example, he viewed morality as a natural outgrowth of instincts that were beneficial to animals living in social groups. He argued that all the differences between humans and apes were explained by a combination of the selective pressures that came from our ancestors moving from the trees to the plains, and sexual selection

Sexual selection

Sexual selection, a concept introduced by Charles Darwin in his 1859 book On the Origin of Species, is a significant element of his theory of natural selection...

. The debate over human origins, and over the degree of human uniqueness continued well into the 20th century.

Alternatives to natural selection

The concept of evolution was widely accepted in scientific circles within a few years of the publication of Origin, but the acceptance of natural selection

Natural selection

as its driving mechanism was much less widespread. The four major alternatives to natural selection in the late 19th century were theistic evolution

Theistic evolution

Theistic evolution or evolutionary creation is a concept that asserts that classical religious teachings about God are compatible with the modern scientific understanding about biological evolution...

, neo-Lamarckism

Lamarckism

, orthogenesis

Orthogenesis

, and saltationism

Saltation (biology)

In biology, ""saltation"" is a sudden change from one generation to the next, that is large, or very large, in comparison with the usual variation of an organism...

. Theistic evolution (a term promoted by Darwin's greatest American advocate Asa Gray

Asa Gray

-References:*Asa Gray. Dictionary of American Biography. American Council of Learned Societies, 1928–1936.*Asa Gray. Encyclopedia of World Biography, 2nd ed. 17 Vols. Gale Research, 1998.*Asa Gray. Plant Sciences. 4 vols. Macmillan Reference USA, 2001....

) was the idea that God intervened in the process of evolution to guide it in such a way that the living world could still be considered to be designed. However, this idea gradually fell out of favor among scientists, as they became more and more committed to the idea of methodological naturalism

Naturalism (philosophy)

and came to believe that direct appeals to supernatural involvement were scientifically unproductive. By 1900, theistic evolution had largely disappeared from professional scientific discussions, although it retained a strong popular following.

In the late 19th century, the term neo-Lamarckism

Lamarckism

came to be associated with the position of naturalists who viewed the inheritance of acquired characteristics as the most important evolutionary mechanism. Advocates of this position included the British writer and Darwin critic Samuel Butler

Samuel Butler (novelist)

Samuel Butler was an iconoclastic Victorian author who published a variety of works. Two of his most famous pieces are the Utopian satire Erewhon and a semi-autobiographical novel published posthumously, The Way of All Flesh...

, the German biologist Ernst Haeckel

Ernst Haeckel

, and the American paleontologist Edward Drinker Cope

Edward Drinker Cope

Edward Drinker Cope was an American paleontologist and comparative anatomist, as well as a noted herpetologist and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy interested in science; he published his first scientific paper at the age of nineteen...

. They considered Lamarckism to be philosophically superior to Darwin's idea of selection acting on random variation. Cope looked for, and thought he found, patterns of linear progression in the fossil record. Inheritance of acquired characteristics was part of Haeckel's recapitulation theory

Recapitulation theory

The theory of recapitulation, also called the biogenetic law or embryological parallelism—and often expressed as "ontogeny recapitulates phylogeny"—is a disproven hypothesis that in developing from embryo to adult, animals go through stages resembling or representing successive stages...

of evolution, which held that the embryological development of an organism repeats its evolutionary history. Critics of neo-Lamarckism, such as the German biologist August Weismann

August Weismann

Friedrich Leopold August Weismann was a German evolutionary biologist. Ernst Mayr ranked him the second most notable evolutionary theorist of the 19th century, after Charles Darwin...

and Alfred Russel Wallace

Alfred Russel Wallace

Alfred Russel Wallace, OM, FRS was a British naturalist, explorer, geographer, anthropologist and biologist...

, pointed out that no one had ever produced solid evidence for the inheritance of acquired characteristics. Despite these criticisms, neo-Lamarckism remained the most popular alternative to natural selection at the end of the 19th century, and would remain the position of some naturalists well into the 20th century.

Orthogenesis

Orthogenesis

was the hypothesis

Hypothesis

A hypothesis is a proposed explanation for a phenomenon. The term derives from the Greek, ὑποτιθέναι – hypotithenai meaning "to put under" or "to suppose". For a hypothesis to be put forward as a scientific hypothesis, the scientific method requires that one can test it...

that life has an innate tendency to change, in a unilinear fashion, towards ever-greater perfection. It had a significant following in the 19th century, and its proponents included the Russian biologist Leo S. Berg and the American paleontologist Henry Fairfield Osborn

Henry Fairfield Osborn

Henry Fairfield Osborn, Sr. ForMemRS was an American geologist, paleontologist, and eugenicist.-Early life and career:...

. Orthogenesis was popular among some paleontologists, who believed that the fossil record showed a gradual and constant unidirectional change. Saltationism was the idea that new species arise as a result of large mutations. It was seen as a much faster alternative to the Darwinian concept of a gradual process of small random variations being acted on by natural selection, and was popular with early geneticists such as Hugo de Vries

Hugo de Vries

Hugo Marie de Vries ForMemRS was a Dutch botanist and one of the first geneticists. He is known chiefly for suggesting the concept of genes, rediscovering the laws of heredity in the 1890s while unaware of Gregor Mendel's work, for introducing the term "mutation", and for developing a mutation...

, William Bateson

William Bateson

William Bateson was an English geneticist and a Fellow of St. John's College, Cambridge...

, and early in his career, T. H. Morgan

Thomas Hunt Morgan

Thomas Hunt Morgan was an American evolutionary biologist, geneticist and embryologist and science author who won the Nobel Prize in Physiology or Medicine in 1933 for discoveries relating the role the chromosome plays in heredity.Morgan received his PhD from Johns Hopkins University in zoology...

. It became the basis of the mutation theory

Mutationism

Mutationism refers to the theory emphasizing mutation as a creative principle and source of discontinuity in evolutionary change, particularly associated with the founders of modern genetics....

of evolution.

Mendelian genetics, biometrics, and mutation

The rediscovery of Gregor Mendel

Gregor Mendel

Gregor Johann Mendel was an Austrian scientist and Augustinian friar who gained posthumous fame as the founder of the new science of genetics. Mendel demonstrated that the inheritance of certain traits in pea plants follows particular patterns, now referred to as the laws of Mendelian inheritance...

's laws of inheritance in 1900 ignited a fierce debate between two camps of biologists. In one camp were the Mendelians

Mendelian inheritance

Mendelian inheritance is a scientific description of how hereditary characteristics are passed from parent organisms to their offspring; it underlies much of genetics...

, who were focused on discrete variations and the laws of inheritance. They were led by William Bateson

William Bateson

William Bateson was an English geneticist and a Fellow of St. John's College, Cambridge...

(who coined the word genetics
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....

) and Hugo de Vries

Hugo de Vries

(who coined the word mutation
Mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...

). Their opponents were the biometricians

Biostatistics

Biostatistics is the application of statistics to a wide range of topics in biology...

, who were interested in the continuous variation of characteristics within populations. Their leaders, Karl Pearson

Karl Pearson

Karl Pearson FRS was an influential English mathematician who has been credited for establishing the disciplineof mathematical statistics....

and Walter Frank Raphael Weldon

Walter Frank Raphael Weldon

Walter Frank Raphael Weldon DSc FRS generally called Raphael Weldon, was an English evolutionary biologist and a founder of biometry...

, followed in the tradition of Francis Galton

Francis Galton

, who had focused on measurement and statistical

Statistics

Statistics is the study of the collection, organization, analysis, and interpretation of data. It deals with all aspects of this, including the planning of data collection in terms of the design of surveys and experiments....

analysis of variation within a population. The biometricians rejected Mendelian genetics on the basis that discrete units of heredity, such as genes, could not explain the continuous range of variation seen in real populations. Weldon's work with crabs and snails provided evidence that selection pressure from the environment could shift the range of variation in wild populations, but the Mendelians maintained that the variations measured by biometricians were too insignificant to account for the evolution of new species.

When T. H. Morgan

Thomas Hunt Morgan

began experimenting with breeding the fruit fly Drosophila melanogaster
Drosophila melanogaster
Drosophila melanogaster is a species of Diptera, or the order of flies, in the family Drosophilidae. The species is known generally as the common fruit fly or vinegar fly. Starting from Charles W...

, he was a saltationist who hoped to demonstrate that a new species could be created in the lab by mutation alone. Instead, the work at his lab between 1910 and 1915 reconfirmed Mendelian genetics and provided solid experimental evidence linking it to chromosomal inheritance. His work also demonstrated that most mutations had relatively small effects, such as a change in eye color, and that rather than creating a new species in a single step, mutations served to increase variation within the existing population.

1920s–1940s

Population genetics

The Mendelian and biometrician models were eventually reconciled with the development of population genetics

Population genetics

. A key step was the work of the British biologist and statistician R.A. Fisher

Ronald Fisher

Sir Ronald Aylmer Fisher FRS was an English statistician, evolutionary biologist, eugenicist and geneticist. Among other things, Fisher is well known for his contributions to statistics by creating Fisher's exact test and Fisher's equation...

. In a series of papers starting in 1918 and culminating in his 1930 book The Genetical Theory of Natural Selection
The Genetical Theory of Natural Selection
The Genetical Theory of Natural Selection is a book by R.A. Fisher first published in 1930 by Clarendon. It is one of the most important books of the modern evolutionary synthesis and is commonly cited in biology books.-Editions:...

, Fisher showed that the continuous variation measured by the biometricians could be produced by the combined action of many discrete genes, and that natural selection

Natural selection

could change gene frequencies

Allele frequency

Allele frequency or Gene frequency is the proportion of all copies of a gene that is made up of a particular gene variant . In other words, it is the number of copies of a particular allele divided by the number of copies of all alleles at the genetic place in a population. It can be expressed for...

in a population, resulting in evolution. In a series of papers beginning in 1924, another British geneticist, J.B.S. Haldane

J. B. S. Haldane

John Burdon Sanderson Haldane FRS , known as Jack , was a British-born geneticist and evolutionary biologist. A staunch Marxist, he was critical of Britain's role in the Suez Crisis, and chose to leave Oxford and moved to India and became an Indian citizen...

, applied statistical analysis to real-world examples of natural selection, such as the evolution of industrial melanism in peppered moths

Peppered moth evolution

The evolution of the peppered moth over the last two hundred years has been studied in detail. Originally, the vast majority of peppered moths had light colouration, which effectively camouflaged them against the light-coloured trees and lichens which they rested upon...

, and showed that natural selection worked at an even faster rate than Fisher assumed.

The American biologist Sewall Wright

Sewall Wright

Sewall Green Wright was an American geneticist known for his influential work on evolutionary theory and also for his work on path analysis. With R. A. Fisher and J.B.S. Haldane, he was a founder of theoretical population genetics. He is the discoverer of the inbreeding coefficient and of...

, who had a background in animal breeding

Animal breeding

Animal breeding is a branch of animal science that addresses the evaluation of the genetic value of domestic livestock...

experiments, focused on combinations of interacting genes, and the effects of inbreeding on small, relatively isolated populations that exhibited genetic drift

Genetic drift

. In 1932, Wright introduced the concept of an adaptive landscape

Fitness landscape

In evolutionary biology, fitness landscapes or adaptive landscapes are used to visualize the relationship between genotypes and reproductive success. It is assumed that every genotype has a well-defined replication rate . This fitness is the "height" of the landscape...

and argued that genetic drift and inbreeding could drive a small, isolated sub-population away from an adaptive peak, allowing natural selection to drive it towards different adaptive peaks. The work of Fisher, Haldane and Wright founded the discipline of population genetics

Population genetics

. This integrated natural selection with Mendelian genetics, which was the critical first step in developing a unified theory of how evolution worked.

Modern evolutionary synthesis

In the first few decades of the 20th century, most field naturalists continued to believe that Lamarckian and orthogenetic mechanisms of evolution provided the best explanation for the complexity they observed in the living world. But as the field of genetics continued to develop, those views became less tenable. Theodosius Dobzhansky

Theodosius Dobzhansky

Theodosius Grygorovych Dobzhansky ForMemRS was a prominent geneticist and evolutionary biologist, and a central figure in the field of evolutionary biology for his work in shaping the unifying modern evolutionary synthesis...

, a postdoctoral worker in T. H. Morgan's lab, had been influenced by the work on genetic diversity by Russia

Russia

Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

n geneticists such as Sergei Chetverikov

Sergei Chetverikov

Sergei Sergeevich Chetverikov was one of the early contributors to the development of the field of genetics...

. He helped to bridge the divide between the foundations of microevolution

Microevolution

Microevolution is the changes in allele frequencies that occur over time within a population. This change is due to four different processes: mutation, selection , gene flow, and genetic drift....

developed by the population geneticists and the patterns of macroevolution

Macroevolution

Macroevolution is evolution on a scale of separated gene pools. Macroevolutionary studies focus on change that occurs at or above the level of species, in contrast with microevolution, which refers to smaller evolutionary changes within a species or population.The process of speciation may fall...

observed by field biologists, with his 1937 book Genetics and the Origin of Species
Genetics and the Origin of Species
Genetics and the Origin of Species is a 1937 book by the twentieth century Ukrainian-American evolutionary biologist Theodosius Dobzhansky and one of the important books of the modern evolutionary synthesis. The book describes the Modern Synthesis of Evolution Theory, also known as Synthetic...

. Dobzhansky examined the genetic diversity of wild populations and showed that, contrary to the assumptions of the population geneticists, these populations had large amounts of genetic diversity, with marked differences between sub-populations. The book also took the highly mathematical work of the population geneticists and put it into a more accessible form. In Great Britain E.B. Ford

E.B. Ford

Edmund Brisco "Henry" Ford FRS Hon. FRCP was a British ecological geneticist. He was a leader among those British biologists who investigated the role of natural selection in nature. As a schoolboy Ford became interested in lepidoptera, the group of insects which includes butterflies and moths...

, the pioneer of ecological genetics

Ecological genetics

Ecological genetics is the study of genetics in natural populations.This contrasts with classical genetics, which works mostly on crosses between laboratory strains, and DNA sequence analysis, which studies genes at the molecular level....

, continued throughout the 1930s and 1940s to demonstrate the power of selection due to ecological factors including the ability to maintain genetic diversity through genetic polymorphisms

Polymorphism (biology)

Polymorphism in biology occurs when two or more clearly different phenotypes exist in the same population of a species — in other words, the occurrence of more than one form or morph...

such as human blood types. Ford's work would contribute to a shift in emphasis during the course of the modern synthesis towards natural selection

Natural selection

over genetic drift

Genetic drift

.

Evolutionary biologist Ernst Mayr was influenced by the work of the German biologist Bernhard Rensch

Bernhard Rensch

Bernhard Rensch was a German evolutionary biologist, and ornithologist who did field work in Indonesia and India. He is probably best known as one of the architects of the modern evolutionary synthesis, which he popularised in Germany...

showing the influence of local environmental factors on the geographic distribution of sub-species and closely related species. Mayr followed up on Dobzhansky's work with the 1942 book Systematics and the Origin of Species, which emphasized the importance of allopatric speciation

Allopatric speciation

Allopatric speciation or geographic speciation is speciation that occurs when biological populations of the same species become isolated due to geographical changes such as mountain building or social changes such as emigration...

in the formation of new species. This form of speciation occurs when the geographical isolation of a sub-population is followed by the development of mechanisms for reproductive isolation

Reproductive isolation

The mechanisms of reproductive isolation or hybridization barriers are a collection of mechanisms, behaviors and physiological processes that prevent the members of two different species that cross or mate from producing offspring, or which ensure that any offspring that may be produced is not...

. Mayr also formulated the biological species concept that defined a species as a group of interbreeding or potentially interbreeding populations that were reproductively isolated from all other populations.

In the 1944 book Tempo and Mode in Evolution
Tempo and Mode in Evolution
Tempo and Mode in Evolution was George Gaylord Simpson's seminal contribution to the evolutionary synthesis, which integrated the facts of paleontology with those of genetics and natural selection....

, George Gaylord Simpson

George Gaylord Simpson

George Gaylord Simpson was an American paleontologist. Simpson was perhaps the most influential paleontologist of the twentieth century, and a major participant in the modern evolutionary synthesis, contributing Tempo and mode in evolution , The meaning of evolution and The major features of...

showed that the fossil record was consistent with the irregular non-directional pattern predicted by the developing evolutionary synthesis, and that the linear trends that earlier paleontologists had claimed supported orthogenesis and neo-Lamarckism did not hold up to closer examination. In 1950, G. Ledyard Stebbins

G. Ledyard Stebbins

George Ledyard Stebbins, Jr. was an American botanist and geneticist who is widely regarded as one of the leading evolutionary biologists of the 20th century. Stebbins received his Ph.D. in botany from Harvard University in 1931. He went on to the University of California, Berkeley, where his work...

published Variation and Evolution in Plants
Variation and Evolution in Plants
Variation and Evolution in Plants is a book written by G. Ledyard Stebbins, published in 1950. It is one of the key publications embodying the modern evolutionary synthesis, as the first comprehensive publication to discuss the relationship between genetics and natural selection in plants. The book...

, which helped to integrate botany

Botany

Botany, plant science, or plant biology is a branch of biology that involves the scientific study of plant life. Traditionally, botany also included the study of fungi, algae and viruses...

into the synthesis. The emerging cross-disciplinary consensus on the workings of evolution would be known as the modern evolutionary synthesis

Modern evolutionary synthesis

The modern evolutionary synthesis is a union of ideas from several biological specialties which provides a widely accepted account of evolution...

. It received its name from the book Evolution: The Modern Synthesis
Evolution: The Modern Synthesis
Evolution: The Modern Synthesis, a 1942 book by Julian Huxley , is one of the most important books of the modern evolutionary synthesis.- Publication history :Allen & Unwin, London...

by Julian Huxley

Julian Huxley

Sir Julian Sorell Huxley FRS was an English evolutionary biologist, humanist and internationalist. He was a proponent of natural selection, and a leading figure in the mid-twentieth century evolutionary synthesis...

.

The evolutionary synthesis provided a conceptual core—in particular, natural selection and Mendelian population genetics—that tied together many, but not all, biological disciplines. It helped establish the legitimacy of evolutionary biology, a primarily historical science, in a scientific climate that favored experimental methods over historical ones. The synthesis also resulted in a considerable narrowing of the range of mainstream evolutionary thought (what Stephen Jay Gould called the "hardening of the synthesis"): by the 1950s, natural selection acting on genetic variation was virtually the only acceptable mechanism of evolutionary change (panselectionism), and macroevolution was simply considered the result of extensive microevolution.

1940s–1960s: Molecular biology and evolution

The middle decades of the 20th century saw the rise of molecular biology

History of molecular biology

The history of molecular biology begins in the 1930s with the convergence of various, previously distinct biological disciplines: biochemistry, genetics, microbiology, and virology...

, and with it an understanding of the chemical nature of genes as sequences of DNA

DNA sequence

The sequence or primary structure of a nucleic acid is the composition of atoms that make up the nucleic acid and the chemical bonds that bond those atoms. Because nucleic acids, such as DNA and RNA, are unbranched polymers, this specification is equivalent to specifying the sequence of...

and of their relationship – through the genetic code

Genetic code

The genetic code is the set of rules by which information encoded in genetic material is translated into proteins by living cells....

– to protein sequences. At the same time, increasingly powerful techniques for analyzing proteins, such as protein electrophoresis

Protein electrophoresis

Protein electrophoresis is a method for analysing the proteins in a fluid or an extract. The electrophoresis may be performed with a small volume of sample in a number of alternative ways with or without a supporting medium: SDS polyacrylamide gel electrophoresis Protein electrophoresis is a method...

and sequencing

Protein sequencing

Protein sequencing is a technique to determine the amino acid sequence of a protein, as well as which conformation the protein adopts and the extent to which it is complexed with any non-peptide molecules...

, brought biochemical phenomena into realm of the synthetic theory of evolution. In the early 1960s, biochemists Linus Pauling

Linus Pauling

Linus Carl Pauling was an American chemist, biochemist, peace activist, author, and educator. He was one of the most influential chemists in history and ranks among the most important scientists of the 20th century...

and Emile Zuckerkandl

Emile Zuckerkandl

Emile Zuckerkandl is an Austrian-American biologist considered one of the founders of the field of molecular evolution. He is best known for introducing, with Linus Pauling, the concept of the molecular clock, which set the stage for the neutral theory of molecular evolution.- Life and work...

proposed the molecular clock hypothesis: that sequence differences between homologous proteins could be used to calculate the time since two species diverged. By 1969, Motoo Kimura

Motoo Kimura

was a Japanese biologist best known for introducing the neutral theory of molecular evolution in 1968. He became one of the most influential theoretical population geneticists. He is remembered in genetics for his innovative use of diffusion equations to calculate the probability of fixation of...

and others provided a theoretical basis for the molecular clock, arguing that—at the molecular level at least—most genetic mutations are neither harmful nor helpful and that mutation

Mutation

and genetic drift

Genetic drift

(rather than natural selection

Natural selection

) cause a large portion of genetic change: the neutral theory of molecular evolution

Neutral theory of molecular evolution

. Studies of protein differences within species also brought molecular data to bear on population genetics by providing estimates of the level of heterozygosity in natural populations.

From the early 1960s, molecular biology was increasingly seen as a threat to the traditional core of evolutionary biology. Established evolutionary biologists—particularly Ernst Mayr, Theodosius Dobzhansky and G. G. Simpson, three of the architects of the modern synthesis—were extremely skeptical of molecular approaches, especially when it came to the connection (or lack thereof) to natural selection

Natural selection

. The molecular-clock hypothesis and the neutral theory were particularly controversial, spawning the neutralist-selectionist debate over the relative importance of mutation, drift and selection, which continued into the 1980s without a clear resolution.

Gene-centered view

In the mid-1960s, George C. Williams

George C. Williams

Professor George Christopher Williams was an American evolutionary biologist.Williams was a professor emeritus of biology at the State University of New York at Stony Brook. He was best known for his vigorous critique of group selection. The work of Williams in this area, along with W. D...

strongly critiqued explanations of adaptations worded in terms of "survival of the species" (group selection

Group selection

In evolutionary biology, group selection refers to the idea that alleles can become fixed or spread in a population because of the benefits they bestow on groups, regardless of the alleles' effect on the fitness of individuals within that group....

arguments). Such explanations were largely replaced by a gene-centered view of evolution

Gene-centered view of evolution

, epitomized by the kin selection

Kin selection

Kin selection refers to apparent strategies in evolution that favor the reproductive success of an organism's relatives, even at a cost to the organism's own survival and reproduction. Charles Darwin was the first to discuss the concept of group/kin selection...

arguments of W. D. Hamilton

W. D. Hamilton

William Donald Hamilton FRS was a British evolutionary biologist, widely recognised as one of the greatest evolutionary theorists of the 20th century....

, George R. Price

George R. Price

George Robert Price was an American population geneticist. Originally a physical chemist and later a science journalist, he moved to London in 1967, where he worked in theoretical biology at the Galton Laboratory, making three important contributions: first, rederiving W.D...

and John Maynard Smith

John Maynard Smith

John Maynard Smith,His surname was Maynard Smith, not Smith, nor was it hyphenated. F.R.S. was a British theoretical evolutionary biologist and geneticist. Originally an aeronautical engineer during the Second World War, he took a second degree in genetics under the well-known biologist J.B.S....

. This viewpoint would be summarized and popularized in the influential 1976 book The Selfish Gene
The Selfish Gene
The Selfish Gene is a book on evolution by Richard Dawkins, published in 1976. It builds upon the principal theory of George C. Williams's first book Adaptation and Natural Selection. Dawkins coined the term "selfish gene" as a way of expressing the gene-centred view of evolution as opposed to the...

by Richard Dawkins

Richard Dawkins

Clinton Richard Dawkins, FRS, FRSL , known as Richard Dawkins, is a British ethologist, evolutionary biologist and author...

. Models of the period showed that group selection was severely limited in its strength; though newer models do admit the possibility of significant multi-level selection.

In 1973, Leigh Van Valen

Leigh Van Valen

Leigh Maiorana Van Valen was an American evolutionary biologist. He was professor emeritus in the Department of Ecology and Evolution at the University of Chicago....

proposed the term "Red Queen

Red Queen's Hypothesis

The Red Queen's Hypothesis, also referred to as Red Queen, Red Queen's race or Red Queen Effect, is an evolutionary hypothesis. The term is taken from the Red Queen's race in Lewis Carroll's Through the Looking-Glass...

", which he took from Through the Looking-Glass
Through the Looking-Glass
Through the Looking-Glass, and What Alice Found There is a work of literature by Lewis Carroll . It is the sequel to Alice's Adventures in Wonderland...

by Lewis Carroll

Lewis Carroll

Charles Lutwidge Dodgson , better known by the pseudonym Lewis Carroll , was an English author, mathematician, logician, Anglican deacon and photographer. His most famous writings are Alice's Adventures in Wonderland and its sequel Through the Looking-Glass, as well as the poems "The Hunting of the...

, to describe a scenario where a species involved in one or more evolutionary arms race

Evolutionary arms race

In evolutionary biology, an evolutionary arms race is an evolutionary struggle between competing sets of co-evolving genes that develop adaptations and counter-adaptations against each other, resembling an arms race, which are also examples of positive feedback...

s would have to constantly change just to keep pace with the species with which it was co-evolving

Co-evolution

In biology, coevolution is "the change of a biological object triggered by the change of a related object." Coevolution can occur at many biological levels: it can be as microscopic as correlated mutations between amino acids in a protein, or as macroscopic as covarying traits between different...

. Hamilton, Williams and others suggested that this idea might explain the evolution of sexual reproduction

Evolution of sex

The evolution of sexual reproduction is currently described by several competing scientific hypotheses. All sexually reproducing organisms derive from a common ancestor which was a single celled eukaryotic species. Many protists reproduce sexually, as do the multicellular plants, animals, and fungi...

: the increased genetic diversity caused by sexual reproduction would help maintain resistance against rapidly evolving parasites, thus making sexual reproduction common, despite the tremendous cost from the gene-centric point of view of a system where only half of an organism's genome

Genome

In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....

is passed on during reproduction. The gene-centric view has also led to an increased interest in Darwin's old idea of sexual selection

Sexual selection

Sexual selection, a concept introduced by Charles Darwin in his 1859 book On the Origin of Species, is a significant element of his theory of natural selection...

, and more recently in topics such as sexual conflict

Sexual conflict

Sexual conflict occurs when the two sexes have conflicting optimal fitness strategies concerning reproduction, particularly the mode and frequency of mating, leading to an evolutionary arms race between males and females. The conflict encompasses the actions and behaviors of both sexes to influence...

and intragenomic conflict

Intragenomic conflict

The selfish gene theory postulates that natural selection will increase the frequency of those genes whose phenotypic effects ensure their successful replication...

Sociobiology

W. D. Hamilton's work on kin selection contributed to the emergence of the discipline of sociobiology

Sociobiology

Sociobiology is a field of scientific study which is based on the assumption that social behavior has resulted from evolution and attempts to explain and examine social behavior within that context. Often considered a branch of biology and sociology, it also draws from ethology, anthropology,...

. The existence of altruistic behaviors

Altruism

Altruism is a concern for the welfare of others. It is a traditional virtue in many cultures, and a core aspect of various religious traditions, though the concept of 'others' toward whom concern should be directed can vary among cultures and religions. Altruism is the opposite of...

has been a difficult problem for evolutionary theorists from the beginning. Significant progress was made in 1964 when Hamilton formulated the inequality in kin selection

Kin selection

known as Hamilton's rule, which showed how eusociality

Eusociality

Eusociality is a term used for the highest level of social organization in a hierarchical classification....

in insects (the existence of sterile worker classes) and many other examples of altruistic behavior could have evolved through kin selection. Other theories followed, some derived from game theory

Game theory

Game theory is a mathematical method for analyzing calculated circumstances, such as in games, where a person’s success is based upon the choices of others...

, such as reciprocal altruism

Reciprocal altruism

In evolutionary biology, reciprocal altruism is a behaviour whereby an organism acts in a manner that temporarily reduces its fitness while increasing another organism's fitness, with the expectation that the other organism will act in a similar manner at a later time...

. In 1975, E.O. Wilson published the influential and highly controversial book Sociobiology: The New Synthesis
Sociobiology: The New Synthesis
Sociobiology: The New Synthesis is a book written by E. O. Wilson, which started the sociobiology debate, one of the great scientific controversies in biology of the 20th century...

which claimed evolutionary theory could help explain many aspects of animal, including human, behavior. Critics of sociobiology, including Stephen Jay Gould

Stephen Jay Gould

Stephen Jay Gould was an American paleontologist, evolutionary biologist, and historian of science. He was also one of the most influential and widely read writers of popular science of his generation....

and Richard Lewontin

Richard Lewontin

Richard Charles "Dick" Lewontin is an American evolutionary biologist, geneticist and social commentator. A leader in developing the mathematical basis of population genetics and evolutionary theory, he pioneered the notion of using techniques from molecular biology such as gel electrophoresis to...

, claimed that sociobiology greatly overstated the degree to which complex human behaviors could be determined by genetic factors. They also claimed that the theories of sociobiologists often reflected their own ideological biases. Despite these criticisms, work has continued in sociobiology and the related discipline of evolutionary psychology

Evolutionary psychology

, including work on other aspects of the altruism problem.

Evolutionary paths and processes

One of the most prominent debates arising during the 1970s was over the theory of punctuated equilibrium

Punctuated equilibrium

Punctuated equilibrium is a theory in evolutionary biology which proposes that most species will exhibit little net evolutionary change for most of their geological history, remaining in an extended state called stasis...

. Niles Eldredge

Niles Eldredge

Niles Eldredge is an American paleontologist, who, along with Stephen Jay Gould, proposed the theory of punctuated equilibrium in 1972.-Education:...

and Stephen Jay Gould

Stephen Jay Gould

proposed that there was a pattern of fossil species that remained largely unchanged for long periods (what they termed stasis), interspersed with relatively brief periods of rapid change during speciation

Speciation

Speciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages...

. Improvements in sequencing

Sequencing

In genetics and biochemistry, sequencing means to determine the primary structure of an unbranched biopolymer...

methods resulted in a large increase of sequenced genome

Genome

s, allowing the testing and refining of evolutionary theories using this huge amount of genome data. Comparisons between these genomes provide insights into the molecular mechanisms of speciation and adaptation. These genomic analyses have produced fundamental changes in the understanding of the evolutionary history of life

Evolutionary history of life

The evolutionary history of life on Earth traces the processes by which living and fossil organisms have evolved since life on Earth first originated until the present day. Earth formed about 4.5 Ga and life appeared on its surface within one billion years...

, such as the proposal of the three-domain system

Three-domain system

by Carl Woese

Carl Woese

Carl Richard Woese is an American microbiologist and physicist. Woese is famous for defining the Archaea in 1977 by phylogenetic taxonomy of 16S ribosomal RNA, a technique pioneered by Woese and which is now standard practice. He was also the originator of the RNA world hypothesis in 1977,...

. Advances in computational hardware and software allow the testing and extrapolation of increasingly advanced evolutionary models and the development of the field of systems biology

Systems biology

Systems biology is a term used to describe a number of trends in bioscience research, and a movement which draws on those trends. Proponents describe systems biology as a biology-based inter-disciplinary study field that focuses on complex interactions in biological systems, claiming that it uses...

. One of the results has been an exchange of ideas between theories of biological evolution and the field of computer science

Computer science

Computer science or computing science is the study of the theoretical foundations of information and computation and of practical techniques for their implementation and application in computer systems...

known as evolutionary computation

Evolutionary computation

In computer science, evolutionary computation is a subfield of artificial intelligence that involves combinatorial optimization problems....

, which attempts to mimic biological evolution for the purpose of developing new computer algorithms. Discoveries in biotechnology

Biotechnology

Biotechnology is a field of applied biology that involves the use of living organisms and bioprocesses in engineering, technology, medicine and other fields requiring bioproducts. Biotechnology also utilizes these products for manufacturing purpose...

now allow the modification of entire genomes, advancing evolutionary studies to the level where future experiments may involve the creation of entirely synthetic organisms.

Microbiology, horizontal gene transfer, and endosymbiosis

Microbiology

Microbiology is the study of microorganisms, which are defined as any microscopic organism that comprises either a single cell , cell clusters or no cell at all . This includes eukaryotes, such as fungi and protists, and prokaryotes...

was largely ignored by early evolutionary theory. This was due to the paucity of morphological traits and the lack of a species concept in microbiology, particularly amongst prokaryote

Prokaryote

The prokaryotes are a group of organisms that lack a cell nucleus , or any other membrane-bound organelles. The organisms that have a cell nucleus are called eukaryotes. Most prokaryotes are unicellular, but a few such as myxobacteria have multicellular stages in their life cycles...

s. Now, evolutionary researchers are taking advantage of their improved understanding of microbial physiology and ecology, produced by the comparative ease of microbial genomics

Genomics

Genomics is a discipline in genetics concerning the study of the genomes of organisms. The field includes intensive efforts to determine the entire DNA sequence of organisms and fine-scale genetic mapping efforts. The field also includes studies of intragenomic phenomena such as heterosis,...

, to explore the taxonomy and evolution of these organisms. These studies are revealing unanticipated levels of diversity amongst microbes.

One particularly important outcome from studies on microbial evolution was the discovery in Japan of horizontal gene transfer

Horizontal gene transfer

Horizontal gene transfer , also lateral gene transfer , is any process in which an organism incorporates genetic material from another organism without being the offspring of that organism...

in 1959. This transfer of genetic material between different species of bacteria was first recognized because it played a major role in the spread of antibiotic resistance

Antibiotic resistance

Antibiotic resistance is a type of drug resistance where a microorganism is able to survive exposure to an antibiotic. While a spontaneous or induced genetic mutation in bacteria may confer resistance to antimicrobial drugs, genes that confer resistance can be transferred between bacteria in a...

. More recently, as knowledge of genome

Genome

s has continued to expand, it has been suggested that lateral transfer of genetic material has played an important role in the evolution of all organisms. These high levels of horizontal gene transfer have led to suggestions that the family tree of today's organisms, the so-called "tree of life", is more similar to an interconnected web or net.

Indeed, the endosymbiotic theory

Endosymbiotic theory

The endosymbiotic theory concerns the mitochondria, plastids , and possibly other organelles of eukaryotic cells. According to this theory, certain organelles originated as free-living bacteria that were taken inside another cell as endosymbionts...

for the origin of organelle

Organelle

In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid bilayer....

s sees a form of horizontal gene transfer as a critical step in the evolution of eukaryote

Eukaryote

A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...

s such as fungi, plants, and animals. The endosymbiotic theory holds that organelles within the cells of eukorytes such as mitochondria and chloroplast

Chloroplast

Chloroplasts are organelles found in plant cells and other eukaryotic organisms that conduct photosynthesis. Chloroplasts capture light energy to conserve free energy in the form of ATP and reduce NADP to NADPH through a complex set of processes called photosynthesis.Chloroplasts are green...

s, had descended from independent bacteria that came to live symbiotically within other cells. It had been suggested in the late 19th century when similarities between mitochondria and bacteria were noted, but largely dismissed until it was revived and championed by Lynn Margulis

Lynn Margulis

Lynn Margulis was an American biologist and University Professor in the Department of Geosciences at the University of Massachusetts Amherst. She is best known for her theory on the origin of eukaryotic organelles, and her contributions to the endosymbiotic theory, which is now generally accepted...

in the 1960s and 70s; Margulis was able to make use of new evidence that such organelles had their own DNA that was inherited independently from that in the cell's nucleus.

Evolutionary developmental biology

In the 1980s and 1990s the tenets of the modern evolutionary synthesis

Modern evolutionary synthesis

The modern evolutionary synthesis is a union of ideas from several biological specialties which provides a widely accepted account of evolution...

came under increasing scrutiny. There was a renewal of structuralist

Structuralism

Structuralism originated in the structural linguistics of Ferdinand de Saussure and the subsequent Prague and Moscow schools of linguistics. Just as structural linguistics was facing serious challenges from the likes of Noam Chomsky and thus fading in importance in linguistics, structuralism...

themes in evolutionary biology in the work of biologists such as Brian Goodwin

Brian Goodwin

Brian Carey Goodwin was a Canadian mathematician and biologist, a Professor Emeritus at the Open University and a key founder of the field of theoretical biology.He made key contributions to the foundations of biomathematics, complex systems and generative models in developmental biology...

and Stuart Kauffman

Stuart Kauffman

Stuart Alan Kauffman is an American theoretical biologist and complex systems researcher concerning the origin of life on Earth...

, which incorporated ideas from cybernetics

Cybernetics

Cybernetics is the interdisciplinary study of the structure of regulatory systems. Cybernetics is closely related to information theory, control theory and systems theory, at least in its first-order form...

and systems theory

Systems theory

Systems theory is the transdisciplinary study of systems in general, with the goal of elucidating principles that can be applied to all types of systems at all nesting levels in all fields of research...

, and emphasized the self-organizing

Self-organization

Self-organization is the process where a structure or pattern appears in a system without a central authority or external element imposing it through planning...

processes of development as factors directing the course of evolution. The evolutionary biologist Stephen Jay Gould

Stephen Jay Gould

revived earlier ideas of heterochrony

Heterochrony

In biology, heterochrony is defined as a developmental change in the timing of events, leading to changes in size and shape. There are two main components, namely the onset and offset of a particular process, and the rate at which the process operates...

, alterations in the relative rates of developmental processes over the course of evolution, to account for the generation of novel forms, and, with the evolutionary biologist Richard Lewontin

Richard Lewontin

, wrote an influential paper in 1979 suggesting that a change in one biological structure, or even a structural novelty, could arise incidentally as an accidental result of selection on another structure, rather than through direct selection for that particular adaptation. They called such incidental structural changes "spandrels

Spandrel (biology)

In evolutionary biology, a Spandrel is a phenotypic characteristic that is a byproduct of the evolution of some other characteristic, rather than a direct product of adaptive selection.-Origin of Term:...

" after an architectural feature. Later, Gould and Vrba discussed the acquisition of new functions by novel structures arising in this fashion, calling them "exaptation

Exaptation

Exaptation, cooption, and preadaptation are related terms referring to shifts in the function of a trait during evolution. For example, a trait can evolve because it served one particular function, but subsequently it may come to serve another. Exaptations are common in both anatomy and behaviour...

s".

Molecular data regarding the mechanisms underlying development

Developmental biology

Developmental biology is the study of the process by which organisms grow and develop. Modern developmental biology studies the genetic control of cell growth, differentiation and "morphogenesis", which is the process that gives rise to tissues, organs and anatomy.- Related fields of study...

accumulated rapidly during the 1980s and '90s. It became clear that the diversity of animal morphology was not the result of different sets of proteins regulating the development of different animals, but from changes in the deployment of a small set of proteins that were common to all animals. These proteins became known as the "developmental toolkit". Such perspectives influenced the disciplines of phylogenetics

Phylogenetics

In biology, phylogenetics is the study of evolutionary relatedness among groups of organisms , which is discovered through molecular sequencing data and morphological data matrices...

, paleontology

Paleontology

and comparative developmental biology, and spawned the new discipline of evolutionary developmental biology

Evolutionary developmental biology

Evolutionary developmental biology is a field of biology that compares the developmental processes of different organisms to determine the ancestral relationship between them, and to discover how developmental processes evolved...

also known as evo-devo.

Macroevolution and microevolution

One of the tenets of the modern evolutionary synthesis

Modern evolutionary synthesis

The modern evolutionary synthesis is a union of ideas from several biological specialties which provides a widely accepted account of evolution...

was that macroevolution

Macroevolution

(the evolution of phylogenic clades at the species level and above) was solely the result of the mechanisms of microevolution

Microevolution

Microevolution is the changes in allele frequencies that occur over time within a population. This change is due to four different processes: mutation, selection , gene flow, and genetic drift....

(changes in gene frequency within populations) operating over an extended period of time. During the last decades of the 20th century some paleontologists raised questions about whether other factors, such as punctuated equilibrium and group selection operating on the level of entire species and even higher level phylogenic clades, needed to be considered to explain patterns in evolution revealed by statistical analysis of the fossil record. Near the end of the 20th century some researchers in evolutionary developmental biology suggested that interactions between the environment and the developmental process might have been the source of some of the structural innovations seen in macroevolution, but other evo-devo researchers maintained that genetic mechanisms visible at the population level are fully sufficient to explain all macorevolution.

Epigenetic inheritance

Another place where developmental biology has led to the questioning of tenets of the modern evolutionary synthesis

Modern evolutionary synthesis

The modern evolutionary synthesis is a union of ideas from several biological specialties which provides a widely accepted account of evolution...

is the field of epigenetics, the study of how environmental factors affect the way genes express themselves during development. By the first decade of the 21st century it had become accepted that in some cases such environmental factors could affect the expression of genes in subsequent generations even though the offspring were not exposed to the same environmental factors, and there had been no genetic changes. This shows that in some cases non genetic changes to an organism can be inherited and it has been suggested that such inheritance can help with adaptation to local conditions and affect evolution. Some have suggested that in certain cases a form of Lamarckian evolution

Lamarckism

may occur.

Omega Point

Pierre Teilhard de Chardin

Pierre Teilhard de Chardin SJ was a French philosopher and Jesuit priest who trained as a paleontologist and geologist and took part in the discovery of both Piltdown Man and Peking Man. Teilhard conceived the idea of the Omega Point and developed Vladimir Vernadsky's concept of Noosphere...

's metaphysical Omega Point Theory describes the gradual development of the universe

Universe

The Universe is commonly defined as the totality of everything that exists, including all matter and energy, the planets, stars, galaxies, and the contents of intergalactic space. Definitions and usage vary and similar terms include the cosmos, the world and nature...

from subatomic particles to human society, which he viewed as its final stage and goal.

Gaia hypothesis

Teilhard de Chardin's ideas have been seen as being connected to the more specific Gaia theory

Gaia hypothesis

The Gaia hypothesis, also known as Gaia theory or Gaia principle, proposes that all organisms and their inorganic surroundings on Earth are closely integrated to form a single and self-regulating complex system, maintaining the conditions for life on the planet.The scientific investigation of the...

by James Lovelock

James Lovelock

James Lovelock, CH, CBE, FRS is an independent scientist, environmentalist and futurologist who lives in Devon, England. He is best known for proposing the Gaia hypothesis, which postulates that the biosphere is a self-regulating entity with the capacity to keep our planet healthy by controlling...

, who proposed that the living and nonliving parts of Earth can be viewed as a complex interacting system with similarities to a single organism. The Gaia hypothesis has also been viewed by Lynn Margulis

Lynn Margulis

and others as an extension of endosymbiosis

Endosymbiont

An endosymbiont is any organism that lives within the body or cells of another organism, i.e. forming an endosymbiosis...

and exosymbiosis

Ectosymbiosis

Ectosymbiosis is symbiosis in which the symbiont lives on the body surface of the host, including internal surfaces such as the lining of the digestive tube and the ducts of glands....

. This modified hypothesis postulates that all living things have a regulatory effect on the Earth's environment that promotes life overall.

External links

UC Berkeley's History of Evolutionary Thought
Darwin's precursors and influences by John Wilkins. Part of the Talk.Origins Archive.
The Alfred Russel Wallace Page

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