Spontaneous generation
Encyclopedia
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(s). The theory was synthesized by Aristotle
, who compiled and expanded the work of prior natural philosophers and the various ancient explanations of the appearance of organisms; it held sway for two millennia. It is generally accepted to have been ultimately disproven in the 19th century by the experiments of Louis Pasteur
, expanding upon the experiments of other scientists before him (such as Francesco Redi
who had performed similar experiments in the 17th century). Ultimately, it was succeeded by germ theory
and cell theory
.
The disproof of ongoing spontaneous generation is no longer controversial, now that the life cycles of various life forms have been well documented. However, the question of abiogenesis
, how living things originally arose from non-living material, remains relevant today.
believed that everything arose out of the elemental nature of the universe, which he called the "apeiron" or "unbounded". According to Hippolytus in the third century CE, Anaximander claimed that living creatures were first formed in the "wet" when acted on by the Sun, and that they were different then than they are now. For example, he claimed humans, in a different form, must have earlier been born mature like other animals, or they would not have survived. Anaximander also claimed that spontaneous generation continued to this day, with aquatic forms being produced directly from lifeless matter.
Anaximenes
, a pupil of Anaximander, thought that air was the element that imparted life, motion and thought, and speculated that there was a primordial terrestrial slime, a mixture of earth and water, which when combined with the sun's heat formed plants, animals and human beings directly.
Xenophanes
traced the origin of man back to the transitional period between the fluid stage of the earth and the formation of land. He too held to a spontaneous generation of fully formed plants and animals under the influence of the sun.
Empedocles
accepted the spontaneous generation of life, but held that there had to be trials of combinations of parts of animals that spontaneously arose. Successful combinations formed the species we now see, unsuccessful forms failed to reproduce.
Anaxagoras
also adopted a terrestrial slime account, although he thought that the seeds of plants existed in the air from the beginning, and of animals in the aether
.
, he stated in no uncertain terms:
According to this theory, living things came forth from nonliving things because the nonliving material contained pneuma
, or "vital heat
". The creature generated was dependent on the proportions of this pneuma and the five elements he believed comprised all matter. While Aristotle recognized that many living things emerged from putrefying matter, he pointed out that the putrefaction was not the source of life, but the byproduct of the action of the "sweet" element of water.
Numerous forms were attributed to various sources. The testacea
ns (shelled molluscs) are characterized by forming by spontaneous generation in mud, but differ based upon the material they grow in — for example, clams
and scallops in sand, oysters in slime, and the barnacle
and the limpet
in the hollows of rocks. Some reddish worm
s form from long-standing snow
which has turned reddish. Another grub
was said to grow out of fire
.
Concerning sexual reproduction
, Aristotle argued that the male parent provided the "form," or soul, that guided development through semen
, and the female parent contributed unorganized matter, allowing the embryo
to grow.
, a Roman
architect
and writer of the 1st century BCE, advised that libraries be placed facing eastwards to benefit from morning light, but not towards the south or the west as those winds generate bookworms
.
Aristotle claimed that eels were lacking in sex
and lacking milt
, spawn
and the passages for either. Rather, he asserted eels emerged from earthworms. Later philosophers dissented. Pliny the Elder
did not argue against the anatomic limits of eels, but stated that eels reproduce by budding, scraping themselves against rocks, liberating particles that become eels. Athenaeus
described eels as entwining and discharging a fluid which would settle on mud and generate life. On the other hand, Athenaeus also dissented towards spontaneous generation, claiming that a variety of anchovy
did not generate from roe
, as Aristotle stated, but rather, from sea foam
.
Augustine of Hippo
discussed spontaneous generation in The City of God and The Literal Meaning of Genesis, citing Biblical passages such as "Let the waters bring forth abundantly the moving creature that hath life" as decrees that would enable ongoing creation. Augustine emphasized that appearing ignorant of the natural world would not cast Christians in a good light. Other writers pointed to the generation of animals at various times in the narrative of the Exodus
, and the incident of the beehive generated in the carcass of the Lion in the story of Samson
in .
From the fall of the Roman Empire
in 5th century to the East-West Schism
in 1054, the influence of Greek science declined, although spontaneous generation generally went unchallenged. New descriptions were made. Of the numerous beliefs, some had doctrinal implications outside of the Book of Genesis. For example, the idea that a variety of bird known as the Barnacle Goose
emerged from a crustacean known as the Goose Barnacle, had implications on the practice of fasting during Lent
. In 1188, Gerald of Wales, after having traveled in Ireland, argued that the "unnatural" generation of barnacle geese was evidence for the Immaculate Conception
. Where the practice of fasting during Lent allowed fish, but prohibited fowl, the idea that the goose was in fact a fish suggested that its consumption be permitted during Lent. The practice was eventually prohibited by decree of Pope Innocent III
in 1215.
Aristotle, in Arabic translation, was reintroduced to Western Europe. During the 13th century, Aristotle reached his greatest acceptance. With the availability of Latin translations Saint Albertus Magnus
and his student, Saint Thomas Aquinas
, raised Aristotelianism to its greatest prominence. Albert wrote a paraphrase of Aristotle, De causis et processu universitatis, in which he removed some and incorporated other commentaries by Arabic scholars. The influential writings of Aquinas, on both the physical and metaphysical, are predominantly Aristotelian, but show numerous other influences.
Spontaneous generation is discussed as a fact in literature well into the Renaissance
. Where, in passing, Shakespeare discusses snakes and crocodiles forming from the mud of the Nile
, Izaak Walton
again raises the question of the origin of eels "as rats and mice, and many other living creatures, are bred in Egypt, by the sun's heat when it shines upon the overflowing of the river...". While the ancient question of the origin of eels remained unanswered and the additional idea that eels reproduced from corruption of age was mentioned, the spontaneous generation of rats and mice engendered no debate.
(1580–1644). He used experimental techniques, such as growing a willow for five years and showing it increased mass while the soil showed a trivial decrease in comparison. As the process of photosynthesis
was not understood, he attributed the increase of mass to the absorption of water. His notes also describe a recipe for mice (a piece of soiled cloth plus wheat for 21 days) and scorpions (basil, placed between two bricks and left in sunlight). His notes suggest he may even have done these things.
Where Aristotle held that the embryo was formed by a coagulation in the uterus, William Harvey
's dissection of deer showed that there was no visible embryo during the first month. Although his work predated the microscope, this led him to suggest that life came from invisible eggs. In the frontispiece of his book Exercitationes de Generatione Animalium (Essays on the Generation of Animals), he made an expression of biogenesis
: "omnia ex ovo" (everything from eggs).
The ancient beliefs were subjected to testing. In 1668, Francesco Redi
challenged the idea that maggots arose spontaneously from rotting meat. In the first major experiment
to challenge spontaneous generation, he placed meat in a variety of sealed, open, and partially covered containers. Realizing that the sealed containers were deprived of air, he used "fine Naples veil", and observed no worm on the meat, but they appeared on the cloth.
In 1745, John Needham
performed a series of experiments on boiled broths. Believing that boiling would kill all living things, he showed that when sealed right after boiling, the broths would cloud, allowing the belief in spontaneous generation to persist. His studies were rigorously scrutinized by his peers and many of them agreed.
Lazzaro Spallanzani
modified the Needham experiment in 1768, attempting to exclude the possibility of introducing a contaminating factor between boiling and sealing. His technique involved boiling the broth in a sealed container with the air partially evacuated to prevent explosions. Although he did not see growth, the exclusion of air left the question of whether air was an essential factor in spontaneous generation.
In 1837, Charles Cagniard de la Tour
, a physicist, and Theodor Schwann
, one of the founders of cell theory, published their independent discovery of yeast
in alcoholic fermentation. They used the microscope
to examine foam left over from the process of brewing beer
. Where Leeuwenhoek described "small spheroid globules", they observed yeast cells undergo cell division
. Fermentation would not occur when sterile air or pure oxygen was introduced if yeast were not present. This suggested that airborne microorganisms, not spontaneous generation, was responsible.
Louis Pasteur
's 1859 experiment put the question to rest. He boiled a meat broth in a flask that had a long neck which curved downward, like a goose. The idea being that the bend in the neck prevented any particles from reaching the broth, while still allowing the free flow of air. The flask remained free of growth for an extended period. When the flask was turned so that particles could fall down the bends, the broth became quickly clouded.
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...
, who compiled and expanded the work of prior natural philosophers and the various ancient explanations of the appearance of organisms; it held sway for two millennia. It is generally accepted to have been ultimately disproven in the 19th century by the experiments of Louis Pasteur
Louis Pasteur
Louis Pasteur was a French chemist and microbiologist born in Dole. He is remembered for his remarkable breakthroughs in the causes and preventions of diseases. His discoveries reduced mortality from puerperal fever, and he created the first vaccine for rabies and anthrax. His experiments...
, expanding upon the experiments of other scientists before him (such as Francesco Redi
Francesco Redi
Francesco Redi was an Italian physician, naturalist, and poet.-Biography:The son of Gregorio Redi and Cecilia de Ghinci was born in Arezzo on February 18, 1626. After schooling with the Jesuits, he attended the University of Pisa...
who had performed similar experiments in the 17th century). Ultimately, it was succeeded by germ theory
Germ theory of disease
The germ theory of disease, also called the pathogenic theory of medicine, is a theory that proposes that microorganisms are the cause of many diseases...
and cell theory
Cell theory
Cell theory refers to the idea that cells are the basic unit of structure in every living thing. Development of this theory during the mid 17th century was made possible by advances in microscopy. This theory is one of the foundations of biology...
.
The disproof of ongoing spontaneous generation is no longer controversial, now that the life cycles of various life forms have been well documented. However, the question of abiogenesis
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...
, how living things originally arose from non-living material, remains relevant today.
Description
Spontaneous generation refers to both the supposed process by which life would systematically emerge from sources other than seeds, eggs or parents and to the theories which explained the apparent phenomenon. The first form is abiogenesis, in which life emerges from non-living matter. This should not be confused for the modern hypothesis of abiogenesis, in which life emerged once and diversified. The second version is heterogenesis (sometimes called xenogenesis), in which one form of life emerges from a different form.Pre-Aristotelian philosophers
As part of his overall attempt to give natural explanations of things that had previously been ascribed to the agency of the gods, AnaximanderAnaximander
Anaximander was a pre-Socratic Greek philosopher who lived in Miletus, a city of Ionia; Milet in modern Turkey. He belonged to the Milesian school and learned the teachings of his master Thales...
believed that everything arose out of the elemental nature of the universe, which he called the "apeiron" or "unbounded". According to Hippolytus in the third century CE, Anaximander claimed that living creatures were first formed in the "wet" when acted on by the Sun, and that they were different then than they are now. For example, he claimed humans, in a different form, must have earlier been born mature like other animals, or they would not have survived. Anaximander also claimed that spontaneous generation continued to this day, with aquatic forms being produced directly from lifeless matter.
Anaximenes
Anaximenes
Anaximenes may refer to:*Anaximenes of Lampsacus , Greek rhetorician and historian*Anaximenes of Miletus , Greek pre-Socratic philosopher*Anaximenes , a lunar crater...
, a pupil of Anaximander, thought that air was the element that imparted life, motion and thought, and speculated that there was a primordial terrestrial slime, a mixture of earth and water, which when combined with the sun's heat formed plants, animals and human beings directly.
Xenophanes
Xenophanes
of Colophon was a Greek philosopher, theologian, poet, and social and religious critic. Xenophanes life was one of travel, having left Ionia at the age of 25 he continued to travel throughout the Greek world for another 67 years. Some scholars say he lived in exile in Siciliy...
traced the origin of man back to the transitional period between the fluid stage of the earth and the formation of land. He too held to a spontaneous generation of fully formed plants and animals under the influence of the sun.
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...
accepted the spontaneous generation of life, but held that there had to be trials of combinations of parts of animals that spontaneously arose. Successful combinations formed the species we now see, unsuccessful forms failed to reproduce.
Anaxagoras
Anaxagoras
Anaxagoras was a Pre-Socratic Greek philosopher. Born in Clazomenae in Asia Minor, Anaxagoras was the first philosopher to bring philosophy from Ionia to Athens. He attempted to give a scientific account of eclipses, meteors, rainbows, and the sun, which he described as a fiery mass larger than...
also adopted a terrestrial slime account, although he thought that the seeds of plants existed in the air from the beginning, and of animals in the aether
Aether (classical element)
According to ancient and medieval science aether , also spelled æther or ether, is the material that fills the region of the universe above the terrestrial sphere.-Mythological origins:...
.
Aristotle
Aristotle lay the foundations of Western natural philosophy. In his book, The History of AnimalsHistory 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:...
, he stated in no uncertain terms:
According to this theory, living things came forth from nonliving things because the nonliving material contained pneuma
Pneuma (Stoic)
In Stoic philosophy, pneuma is the concept of the "breath of life," a mixture of the elements air and fire . Originating among Greek medical writers who locate human vitality in the breath, pneuma for the Stoics is the active, generative principle that organizes both the individual and the cosmos...
, or "vital heat
Vital heat
Vital heat, also called innate or natural heat, or calidum innatum, is a term that has generally referred to the heat produced within the body, usually the heat produced by the heart and the circulatory system....
". The creature generated was dependent on the proportions of this pneuma and the five elements he believed comprised all matter. While Aristotle recognized that many living things emerged from putrefying matter, he pointed out that the putrefaction was not the source of life, but the byproduct of the action of the "sweet" element of water.
Numerous forms were attributed to various sources. The testacea
Testacea
Testacea is an order of rhizopod, which consists of testate amoeboid organisms....
ns (shelled molluscs) are characterized by forming by spontaneous generation in mud, but differ based upon the material they grow in — for example, clams
CLaMS
CLaMS is a modular chemistry transport model system developed at Forschungszentrum Jülich, Germany. CLaMS was first described by McKenna et al. and was expanded into three dimensions by Konopka et al....
and scallops in sand, oysters in slime, and the barnacle
Barnacle
A barnacle is a type of arthropod belonging to infraclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosive settings. They are sessile suspension feeders, and have...
and the limpet
Limpet
Limpet is a common name for a number of different kinds of saltwater and freshwater snails ; it is applied to those snails that have a simple shell which is more or less conical in shape, and either is not spirally coiled, or appears not to be coiled in the adult snails.The name limpet is most...
in the hollows of rocks. Some reddish worm
Worm
The term worm refers to an obsolete taxon used by Carolus Linnaeus and Jean-Baptiste Lamarck for all non-arthropod invertebrate animals, and stems from the Old English word wyrm. Currently it is used to describe many different distantly-related animals that typically have a long cylindrical...
s form from long-standing snow
Snow
Snow is a form of precipitation within the Earth's atmosphere in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. Since snow is composed of small ice particles, it is a granular material. It has an open and therefore soft structure, unless packed by...
which has turned reddish. Another grub
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
was said to grow out of fire
Fire
Fire is the rapid oxidation of a material in the chemical process of combustion, releasing heat, light, and various reaction products. Slower oxidative processes like rusting or digestion are not included by this definition....
.
Concerning sexual reproduction
Sexual reproduction
Sexual reproduction is the creation of a new organism by combining the genetic material of two organisms. There are two main processes during sexual reproduction; they are: meiosis, involving the halving of the number of chromosomes; and fertilization, involving the fusion of two gametes and the...
, Aristotle argued that the male parent provided the "form," or soul, that guided development through semen
Semen
Semen is an organic fluid, also known as seminal fluid, that may contain spermatozoa. It is secreted by the gonads and other sexual organs of male or hermaphroditic animals and can fertilize female ova...
, and the female parent contributed unorganized matter, allowing the embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
to grow.
Classical writers after Aristotle
VitruviusVitruvius
Marcus Vitruvius Pollio was a Roman writer, architect and engineer, active in the 1st century BC. He is best known as the author of the multi-volume work De Architectura ....
, a Roman
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....
architect
Architect
An architect is a person trained in the planning, design and oversight of the construction of buildings. To practice architecture means to offer or render services in connection with the design and construction of a building, or group of buildings and the space within the site surrounding the...
and writer of the 1st century BCE, advised that libraries be placed facing eastwards to benefit from morning light, but not towards the south or the west as those winds generate bookworms
Bookworm (insect)
Bookworm is a popular generalization for any insect which supposedly bores through books.Actual book-borers are uncommon. Both the larvae of the death watch beetle and the common furniture beetle will tunnel through wood and paper if it is nearby the wood.A major book-feeding insect is the book...
.
Aristotle claimed that eels were lacking in sex
Sex
In biology, sex is a process of combining and mixing genetic traits, often resulting in the specialization of organisms into a male or female variety . Sexual reproduction involves combining specialized cells to form offspring that inherit traits from both parents...
and lacking milt
Milt
Milt is the seminal fluid of fish, mollusks, and certain other water-dwelling animals who reproduce by spraying this fluid, which contains the sperm, onto roe .-Milt as food:...
, spawn
Spawn (biology)
Spawn refers to the eggs and sperm released or deposited, usually into water, by aquatic animals. As a verb, spawn refers to the process of releasing the eggs and sperm, also called spawning...
and the passages for either. Rather, he asserted eels emerged from earthworms. Later philosophers dissented. 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...
did not argue against the anatomic limits of eels, but stated that eels reproduce by budding, scraping themselves against rocks, liberating particles that become eels. Athenaeus
Athenaeus
Athenaeus , of Naucratis in Egypt, Greek rhetorician and grammarian, flourished about the end of the 2nd and beginning of the 3rd century AD...
described eels as entwining and discharging a fluid which would settle on mud and generate life. On the other hand, Athenaeus also dissented towards spontaneous generation, claiming that a variety of anchovy
Anchovy
Anchovies are a family of small, common salt-water forage fish. There are 144 species in 17 genera, found in the Atlantic, Indian, and Pacific Oceans. Anchovies are usually classified as an oily fish.-Description:...
did not generate from roe
Roe
Roe or hard roe is the fully ripe internal egg masses in the ovaries, or the released external egg masses of fish and certain marine animals, such as shrimp, scallop and sea urchins...
, as Aristotle stated, but rather, from sea foam
Sea foam
Sea foam is a type of foam that appears in bodies of salt water. It can also refer to:*sponge toffee, a type of candy*A shade of the color green*A brand of fuel additive...
.
Adoption in Christianity
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...
discussed spontaneous generation in The City of God and The Literal Meaning of Genesis, citing Biblical passages such as "Let the waters bring forth abundantly the moving creature that hath life" as decrees that would enable ongoing creation. Augustine emphasized that appearing ignorant of the natural world would not cast Christians in a good light. Other writers pointed to the generation of animals at various times in the narrative of the Exodus
The Exodus
The Exodus is the story of the departure of the Israelites from ancient Egypt described in the Hebrew Bible.Narrowly defined, the term refers only to the departure from Egypt described in the Book of Exodus; more widely, it takes in the subsequent law-givings and wanderings in the wilderness...
, and the incident of the beehive generated in the carcass of the Lion in the story of Samson
Samson
Samson, Shimshon ; Shamshoun or Sampson is the third to last of the Judges of the ancient Israelites mentioned in the Tanakh ....
in .
From the fall of the Roman Empire
Decline of the Roman Empire
The decline of the Roman Empire refers to the gradual societal collapse of the Western Roman Empire. Many theories of causality prevail, but most concern the disintegration of political, economic, military, and other social institutions, in tandem with foreign invasions and usurpers from within the...
in 5th century to the East-West Schism
East-West Schism
The East–West Schism of 1054, sometimes known as the Great Schism, formally divided the State church of the Roman Empire into Eastern and Western branches, which later became known as the Eastern Orthodox Church and the Roman Catholic Church, respectively...
in 1054, the influence of Greek science declined, although spontaneous generation generally went unchallenged. New descriptions were made. Of the numerous beliefs, some had doctrinal implications outside of the Book of Genesis. For example, the idea that a variety of bird known as the Barnacle Goose
Barnacle Goose
The Barnacle Goose belongs to the genus Branta of black geese, which contains species with largely black plumage, distinguishing them from the grey Anser species...
emerged from a crustacean known as the Goose Barnacle, had implications on the practice of fasting during Lent
Lent
In the Christian tradition, Lent is the period of the liturgical year from Ash Wednesday to Easter. The traditional purpose of Lent is the preparation of the believer – through prayer, repentance, almsgiving and self-denial – for the annual commemoration during Holy Week of the Death and...
. In 1188, Gerald of Wales, after having traveled in Ireland, argued that the "unnatural" generation of barnacle geese was evidence for the Immaculate Conception
Immaculate Conception
The Immaculate Conception of Mary is a dogma of the Roman Catholic Church, according to which the Virgin Mary was conceived without any stain of original sin. It is one of the four dogmata in Roman Catholic Mariology...
. Where the practice of fasting during Lent allowed fish, but prohibited fowl, the idea that the goose was in fact a fish suggested that its consumption be permitted during Lent. The practice was eventually prohibited by decree of Pope Innocent III
Pope Innocent III
Pope Innocent III was Pope from 8 January 1198 until his death. His birth name was Lotario dei Conti di Segni, sometimes anglicised to Lothar of Segni....
in 1215.
Aristotle, in Arabic translation, was reintroduced to Western Europe. During the 13th century, Aristotle reached his greatest acceptance. With the availability of Latin translations Saint Albertus Magnus
Albertus Magnus
Albertus Magnus, O.P. , also known as Albert the Great and Albert of Cologne, is a Catholic saint. He was a German Dominican friar and a bishop, who achieved fame for his comprehensive knowledge of and advocacy for the peaceful coexistence of science and religion. Those such as James A. Weisheipl...
and his student, Saint 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...
, raised Aristotelianism to its greatest prominence. Albert wrote a paraphrase of Aristotle, De causis et processu universitatis, in which he removed some and incorporated other commentaries by Arabic scholars. The influential writings of Aquinas, on both the physical and metaphysical, are predominantly Aristotelian, but show numerous other influences.
Spontaneous generation is discussed as a fact in literature well into 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...
. Where, in passing, Shakespeare discusses snakes and crocodiles forming from the mud of the Nile
Nile
The Nile is a major north-flowing river in North Africa, generally regarded as the longest river in the world. It is long. It runs through the ten countries of Sudan, South Sudan, Burundi, Rwanda, Democratic Republic of the Congo, Tanzania, Kenya, Ethiopia, Uganda and Egypt.The Nile has two major...
, Izaak Walton
Izaak Walton
Izaak Walton was an English writer. Best known as the author of The Compleat Angler, he also wrote a number of short biographies which have been collected under the title of Walton's Lives.-Biography:...
again raises the question of the origin of eels "as rats and mice, and many other living creatures, are bred in Egypt, by the sun's heat when it shines upon the overflowing of the river...". While the ancient question of the origin of eels remained unanswered and the additional idea that eels reproduced from corruption of age was mentioned, the spontaneous generation of rats and mice engendered no debate.
Scientific method
The last great proponent, as experimentation began to transform science, was Jan Baptist van HelmontJan Baptist van Helmont
Jan Baptist van Helmont was an early modern period Flemish chemist, physiologist, and physician. He worked during the years just after Paracelsus and iatrochemistry, and is sometimes considered to be "the founder of pneumatic chemistry"...
(1580–1644). He used experimental techniques, such as growing a willow for five years and showing it increased mass while the soil showed a trivial decrease in comparison. As the process of photosynthesis
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
was not understood, he attributed the increase of mass to the absorption of water. His notes also describe a recipe for mice (a piece of soiled cloth plus wheat for 21 days) and scorpions (basil, placed between two bricks and left in sunlight). His notes suggest he may even have done these things.
Where Aristotle held that the embryo was formed by a coagulation in the uterus, William Harvey
William Harvey
William Harvey was an English physician who was the first person to describe completely and in detail the systemic circulation and properties of blood being pumped to the body by the heart...
's dissection of deer showed that there was no visible embryo during the first month. Although his work predated the microscope, this led him to suggest that life came from invisible eggs. In the frontispiece of his book Exercitationes de Generatione Animalium (Essays on the Generation of Animals), he made an expression of biogenesis
Biogenesis
Biogenesis is the law that living things come only from other living things, e.g. a spider lays eggs, which develop into spiders. It may also refer to biochemical processes of production in living organisms.-Spontaneous generation:...
: "omnia ex ovo" (everything from eggs).
Francesco Redi
Francesco Redi was an Italian physician, naturalist, and poet.-Biography:The son of Gregorio Redi and Cecilia de Ghinci was born in Arezzo on February 18, 1626. After schooling with the Jesuits, he attended the University of Pisa...
challenged the idea that maggots arose spontaneously from rotting meat. In the first major experiment
Experiment
An experiment is a methodical procedure carried out with the goal of verifying, falsifying, or establishing the validity of a hypothesis. Experiments vary greatly in their goal and scale, but always rely on repeatable procedure and logical analysis of the results...
to challenge spontaneous generation, he placed meat in a variety of sealed, open, and partially covered containers. Realizing that the sealed containers were deprived of air, he used "fine Naples veil", and observed no worm on the meat, but they appeared on the cloth.
In 1745, John Needham
John Needham
John Turberville Needham FRS was an English biologist and Roman Catholic priest.He was first exposed to natural philosophy while in seminary school and later published a paper which, while the subject was mostly about geology, described the mechanics of pollen and won recognition in the botany...
performed a series of experiments on boiled broths. Believing that boiling would kill all living things, he showed that when sealed right after boiling, the broths would cloud, allowing the belief in spontaneous generation to persist. His studies were rigorously scrutinized by his peers and many of them agreed.
Lazzaro Spallanzani
Lazzaro Spallanzani
Lazzaro Spallanzani was an Italian Catholic priest, biologist and physiologist who made important contributions to the experimental study of bodily functions, animal reproduction, and essentially discovered echolocation...
modified the Needham experiment in 1768, attempting to exclude the possibility of introducing a contaminating factor between boiling and sealing. His technique involved boiling the broth in a sealed container with the air partially evacuated to prevent explosions. Although he did not see growth, the exclusion of air left the question of whether air was an essential factor in spontaneous generation.
In 1837, Charles Cagniard de la Tour
Charles Cagniard de la Tour
Charles Cagniard de la Tour was a French engineer and physicist.-Biography:Charles Cagniard was born in Paris, and after attending the École Polytechnique became one of the ingénieurs géographiques. He was made a baron in 1818...
, a physicist, and Theodor Schwann
Theodor Schwann
Theodor Schwann was a German physiologist. His many contributions to biology include the development of cell theory, the discovery of Schwann cells in the peripheral nervous system, the discovery and study of pepsin, the discovery of the organic nature of yeast, and the invention of the term...
, one of the founders of cell theory, published their independent discovery of yeast
Yeast
Yeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with 1,500 species currently described estimated to be only 1% of all fungal species. Most reproduce asexually by mitosis, and many do so by an asymmetric division process called budding...
in alcoholic fermentation. They used the microscope
Microscope
A microscope is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy...
to examine foam left over from the process of brewing beer
Beer
Beer is the world's most widely consumed andprobably oldest alcoholic beverage; it is the third most popular drink overall, after water and tea. It is produced by the brewing and fermentation of sugars, mainly derived from malted cereal grains, most commonly malted barley and malted wheat...
. Where Leeuwenhoek described "small spheroid globules", they observed yeast cells undergo cell division
Cell division
Cell division is the process by which a parent cell divides into two or more daughter cells . Cell division is usually a small segment of a larger cell cycle. This type of cell division in eukaryotes is known as mitosis, and leaves the daughter cell capable of dividing again. The corresponding sort...
. Fermentation would not occur when sterile air or pure oxygen was introduced if yeast were not present. This suggested that airborne microorganisms, not spontaneous generation, was responsible.
Louis Pasteur
Louis Pasteur
Louis Pasteur was a French chemist and microbiologist born in Dole. He is remembered for his remarkable breakthroughs in the causes and preventions of diseases. His discoveries reduced mortality from puerperal fever, and he created the first vaccine for rabies and anthrax. His experiments...
's 1859 experiment put the question to rest. He boiled a meat broth in a flask that had a long neck which curved downward, like a goose. The idea being that the bend in the neck prevented any particles from reaching the broth, while still allowing the free flow of air. The flask remained free of growth for an extended period. When the flask was turned so that particles could fall down the bends, the broth became quickly clouded.