Evolutionary taxonomy
Encyclopedia
Evolutionary taxonomy
, evolutionary systematics or Darwinian classification is a branch of biological classification
that seeks to classify organism
s using a combination of phylogenetic
relationship and overall similarity. This type of taxonomy considers taxa rather than single species, so that groups of species give rise to new groups. The concept found its current form in the modern evolutionary synthesis
of the early 1940s.
Evolutionary taxonomy differs from strict pre-Darwinian Linnaean taxonomy
, which produces orderly lists rather than trees
. Also, unlike cladism
which only maps phylogeny, evolutionary taxonomy also offer a biological classification system
. While in phylogeny where each taxon
must consist of a single ancestral node and all its descendants, evolutionary taxonomy allows for groups to be excluded from their parent taxa (e.g. dinosaurs are not considered to include birds, but to have given rise to them), thus allowing for paraphyletic
taxa.
was an established discipline when Darwin formulated his theory of evolution
. The idea of the Linnaean taxonomy as translating into a sort of dendrogram
of the Animal
- and Plant
Kingdoms
was formulated toward the end of the 18th century, well before the On the Origin of Species was published. Among early works exploring the idea of a transmutation of species
was Erasmus Darwin
's 1796 Zoönomia
and Jean-Baptiste Lamarck
's Philosophie Zoologique of 1809. The idea was popularised in the Anglophone world by the speculative, but widely read Vestiges of the Natural History of Creation
, published anonymously by Robert Chambers in 1844.
With Darwin's theory, this thought got a theoretical basis, and Tree of Life
representations became popular in scientific works. Very limited knowledge of the fossil record
at the time hindered the drawing of specific inferences about the ancestors of modern groups. Bout in Vestiges of the Natural History of Creation and On the Origin of Species, the ancestor remained largely a hypothetical species, and Darwin was primarily occupied with showing the principle, and very carefully refrained from speculating on relationship between living or fossil organisms, using theoretical examples only.
One of the first fossil groups to be recognized was dinosaur
s, formally named by Richard Owen
in 1842. With Darwin's theory of evolution being known, Thomas Henry Huxley used the fossils of Archaeopteryx
and Hesperornis
to pronounce the bird
s descendants of the dinosaurs. Thus, a group of extant animals could be tied to a fossil group. The resulting description, that of dinosaurs "giving rise to" or being "the ancestors of" birds, is the essential hallmark of evolutionary taxonomic thinking.
worked to understand the history of animals through the ages by linking together known groups The Tree of life
was slowly being mapped out, with fossil groups taking up their position in the tree as understanding increased. With the modern evolutionary synthesis
of the early 1940s, an essentially modern understanding of evolution of the major groups was in place.
These groups still retained their formal Linnaean taxonomic rank
s, giving rise to a number of units that were paraphyletic
, i.e. where the descendants were considered a part of the daughter group rather than that of the ancestral group. Particularly on the level of order
s and class
es, most of the traditional vertebrate
systematic units are paraphyletic, representing natural evolutionary grade
s rather than clade
s.
. For evolutionary systematicists, monophyletic means only that a group derives from a single common ancestor included in the group, whereas for cladists it also means that the group includes all species descended from that group. The term holophyletic
has been proposed for the latter meaning.
The product of evolutionary systematics is a division according to Linnaean taxonomy
(which can then be used to form tentative conclusions about phylogeny); the product of a cladistic classification is a cladogram
, which can then be used to recommend a taxonomy.
Cladistics collects character data only from the taxa being classified. It does not consider the inferred characters of ancestors.
Evolutionary systematics also differs in method from cladistics. Cladistics involves collecting data and feeding it into a computer program. Evolutionary systematics involves a researcher following flexible guidelines which consider various kinds of evidence (which need not be represented as discrete alternatives).
Other debates between evolutionary systematists and cladists are not about the underlying approach, but on details. One is whether there is a danger of artificial classifications when preparing a classification using molecular phylogeny
based on only a single gene
or part of a gene. Another is whether it is sufficient to study DNA from chloroplast
s, mitochondria
, and ribosome
s, as opposed to non-ribosomal nuclear DNA
.
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...
, evolutionary systematics or Darwinian classification is a branch of biological classification
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....
that seeks to classify organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
s using a combination of phylogenetic
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...
relationship and overall similarity. This type of taxonomy considers taxa rather than single species, so that groups of species give rise to new groups. The concept found its current form in 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...
of the early 1940s.
Evolutionary taxonomy differs from strict pre-Darwinian Linnaean taxonomy
Linnaean taxonomy
Linnaean taxonomy can mean either of two related concepts:# the particular form of biological classification set up by Carl Linnaeus, as set forth in his Systema Naturæ and subsequent works...
, which produces orderly lists rather than trees
Phylogenetic tree
A phylogenetic tree or evolutionary tree is a branching diagram or "tree" showing the inferred evolutionary relationships among various biological species or other entities based upon similarities and differences in their physical and/or genetic characteristics...
. Also, unlike cladism
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
which only maps phylogeny, evolutionary taxonomy also offer a biological classification system
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....
. While in phylogeny where each taxon
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
must consist of a single ancestral node and all its descendants, evolutionary taxonomy allows for groups to be excluded from their parent taxa (e.g. dinosaurs are not considered to include birds, but to have given rise to them), thus allowing for paraphyletic
Paraphyly
A group of taxa is said to be paraphyletic if the group consists of all the descendants of a hypothetical closest common ancestor minus one or more monophyletic groups of descendants...
taxa.
Origin of evolutionary taxonomy
Linnaean taxonomyLinnaean taxonomy
Linnaean taxonomy can mean either of two related concepts:# the particular form of biological classification set up by Carl Linnaeus, as set forth in his Systema Naturæ and subsequent works...
was an established discipline when Darwin formulated his theory of evolution
Evolution
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...
. The idea of the Linnaean taxonomy as translating into a sort of dendrogram
Dendrogram
A dendrogram is a tree diagram frequently used to illustrate the arrangement of the clusters produced by hierarchical clustering...
of the 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...
- and Plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
Kingdoms
Kingdom (biology)
In biology, kingdom is a taxonomic rank, which is either the highest rank or in the more recent three-domain system, the rank below domain. Kingdoms are divided into smaller groups called phyla or divisions in botany...
was formulated toward the end of the 18th century, well before the On the Origin of Species was published. Among early works exploring the idea of a 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...
was 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...
's 1796 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...
and 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...
's Philosophie Zoologique of 1809. The idea was popularised in the Anglophone world by the speculative, but widely read 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...
, published anonymously by Robert Chambers in 1844.
With Darwin's theory, this thought got a theoretical basis, and 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...
representations became popular in scientific works. Very limited knowledge of the fossil record
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
at the time hindered the drawing of specific inferences about the ancestors of modern groups. Bout in Vestiges of the Natural History of Creation and On the Origin of Species, the ancestor remained largely a hypothetical species, and Darwin was primarily occupied with showing the principle, and very carefully refrained from speculating on relationship between living or fossil organisms, using theoretical examples only.
One of the first fossil groups to be recognized was dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
s, formally named by 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...
in 1842. With Darwin's theory of evolution being known, Thomas Henry Huxley used the fossils 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"...
and Hesperornis
Hesperornis
Hesperornis is a genus of flightless aquatic birds that spanned the first half of the Campanian age of the Late Cretaceous period . One of the lesser-known discoveries of the paleontologist O. C. Marsh in the late 19th century Bone Wars, it was an important early find in the history of avian...
to pronounce the bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s descendants of the dinosaurs. Thus, a group of extant animals could be tied to a fossil group. The resulting description, that of dinosaurs "giving rise to" or being "the ancestors of" birds, is the essential hallmark of evolutionary taxonomic thinking.
The Tree of Life
As more and more fossil groups were found and recognized in the late 19th and early 20th century, palaeontologistsPaleontology
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...
worked to understand the history of animals through the ages by linking together known groups The 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...
was slowly being mapped out, with fossil groups taking up their position in the tree as understanding increased. With 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...
of the early 1940s, an essentially modern understanding of evolution of the major groups was in place.
These groups still retained their formal Linnaean taxonomic rank
Taxonomic rank
In biological classification, rank is the level in a taxonomic hierarchy. Examples of taxonomic ranks are species, genus, family, and class. Each rank subsumes under it a number of less general categories...
s, giving rise to a number of units that were paraphyletic
Paraphyly
A group of taxa is said to be paraphyletic if the group consists of all the descendants of a hypothetical closest common ancestor minus one or more monophyletic groups of descendants...
, i.e. where the descendants were considered a part of the daughter group rather than that of the ancestral group. Particularly on the level of order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
s and class
Class (biology)
In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...
es, most of the traditional 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...
systematic units are paraphyletic, representing natural evolutionary grade
Evolutionary grade
In alpha taxonomy, a grade refers to a taxon united by a level of morphological or physiological complexity. The term was coined by British biologist Julian Huxley, to contrast with clade, a strictly phylogenetic unit.-Definition:...
s rather than clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
s.
Difference from cladistic taxonomy
The two approaches differ in the use of the word monophyleticMonophyly
In common cladistic usage, a monophyletic group is a taxon which forms a clade, meaning that it contains all the descendants of the possibly hypothetical closest common ancestor of the members of the group. The term is synonymous with the uncommon term holophyly...
. For evolutionary systematicists, monophyletic means only that a group derives from a single common ancestor included in the group, whereas for cladists it also means that the group includes all species descended from that group. The term holophyletic
Holophyly
Holophyletic is a term posited as a semantically correct replacement for the term monophyletic as used by cladists...
has been proposed for the latter meaning.
The product of evolutionary systematics is a division according to Linnaean taxonomy
Linnaean taxonomy
Linnaean taxonomy can mean either of two related concepts:# the particular form of biological classification set up by Carl Linnaeus, as set forth in his Systema Naturæ and subsequent works...
(which can then be used to form tentative conclusions about phylogeny); the product of a cladistic classification is a cladogram
Cladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
, which can then be used to recommend a taxonomy.
Cladistics collects character data only from the taxa being classified. It does not consider the inferred characters of ancestors.
Evolutionary systematics also differs in method from cladistics. Cladistics involves collecting data and feeding it into a computer program. Evolutionary systematics involves a researcher following flexible guidelines which consider various kinds of evidence (which need not be represented as discrete alternatives).
Other debates between evolutionary systematists and cladists are not about the underlying approach, but on details. One is whether there is a danger of artificial classifications when preparing a classification using molecular phylogeny
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...
based on only a single gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
or part of a gene. Another is whether it is sufficient to study DNA from 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, mitochondria
Mitochondrion
In cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryotic cells. These organelles range from 0.5 to 1.0 micrometers in diameter...
, and ribosome
Ribosome
A ribosome is a component of cells that assembles the twenty specific amino acid molecules to form the particular protein molecule determined by the nucleotide sequence of an RNA molecule....
s, as opposed to non-ribosomal nuclear DNA
Nuclear DNA
Nuclear DNA, nuclear deoxyribonucleic acid , is DNA contained within a nucleus of eukaryotic organisms. In mammals and vertebrates, nuclear DNA encodes more of the genome than the mitochondrial DNA and is composed of information inherited from two parents, one male, and one female, rather than...
.