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Comparative anatomy is the study of similarities and differences in the
anatomy Anatomy () is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having i ...
of different
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...
. It is closely related to
evolutionary biology Evolutionary biology is the subfield of biology that studies the evolutionary processes (natural selection, common descent, speciation) that produced the diversity of life on Earth. It is also defined as the study of the history of life ...
and
phylogeny A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological s ...
(the
evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
of species). The science began in the classical era, continuing in the early modern period with work by Pierre Belon who noted the similarities of the skeletons of birds and humans. Comparative anatomy has provided
evidence of common descent Evidence of common descent of living organisms has been discovered by scientists researching in a variety of disciplines over many decades, demonstrating that all life on Earth comes from a single ancestor. This forms an important part of the ev ...
, and has assisted in the classification of animals.


History

The first specifically anatomical investigation separate from a surgical or medical procedure is associated by Alcmaeon of Croton.
Leonardo da Vinci Leonardo di ser Piero da Vinci (15 April 14522 May 1519) was an Italian polymath of the High Renaissance who was active as a painter, draughtsman, engineer, scientist, theorist, sculptor, and architect. While his fame initially rested on ...
made notes for a planned anatomical treatise in which he intended to compare the hands of various animals including bears. Pierre Belon, a French naturalist born in 1517, conducted research and held discussions on
dolphin A dolphin is an aquatic mammal within the infraorder Cetacea. Dolphin species belong to the families Delphinidae (the oceanic dolphins), Platanistidae (the Indian river dolphins), Iniidae (the New World river dolphins), Pontoporiidae (the b ...
embryos as well as the comparisons between the skeletons of birds to the skeletons of humans. His research led to modern comparative anatomy. Around the same time, Andreas Vesalius was also making some strides of his own. A young anatomist of Flemish descent made famous by a penchant for amazing charts, he was systematically investigating and correcting the anatomical knowledge of the Greek physician Galen. He noticed that many of Galen's observations were not even based on actual humans. Instead, they were based on animals such as apes, monkeys, and oxen. In fact, he entreated his students to do the following, in substitution for human skeletons, as cited by Edward Tyson : "If you can't happen to see any of these, dissect an Ape, carefully view each Bone, &c. ..." Then he advises what sort of Apes to make choice of, as most resembling a Man : And conclude "One ought to know the Structure of all the Bones either in a Humane Body, or in an Apes ; 'tis best in both ; and then to go to the Anatomy of the Muscles." Up until that point, Galen and his teachings had been the authority on human anatomy. The irony is that Galen himself had emphasized the fact that one should make one's own observations instead of using those of another, but this advice was lost during the numerous translations of his work. As Vesalius began to uncover these mistakes, other physicians of the time began to trust their own observations more than those of Galen. An interesting observation made by some of these physicians was the presence of homologous structures in a wide variety of animals which included humans. These observations were later used by Darwin as he formed his theory of
Natural Selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Cha ...
. Edward Tyson is regarded as the founder of modern comparative anatomy. He is credited with determining that
whale Whales are a widely distributed and diverse group of fully aquatic placental marine mammals. As an informal and colloquial grouping, they correspond to large members of the infraorder Cetacea, i.e. all cetaceans apart from dolphins and ...
s and
dolphin A dolphin is an aquatic mammal within the infraorder Cetacea. Dolphin species belong to the families Delphinidae (the oceanic dolphins), Platanistidae (the Indian river dolphins), Iniidae (the New World river dolphins), Pontoporiidae (the b ...
s are, in fact, mammals. Also, he concluded that
chimpanzee The chimpanzee (''Pan troglodytes''), also known as simply the chimp, is a species of great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. When its close relative t ...
s are more similar to humans than to monkeys because of their arms. Marco Aurelio Severino also compared various animals, including birds, in his ''Zootomia democritaea'', one of the first works of comparative anatomy. In the 18th and 19th century, great anatomists like George Cuvier, Richard Owen and Thomas Henry Huxley revolutionized our understanding of the basic build and systematics of vertebrates, laying the foundation for
Charles Darwin Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all species of life have descended ...
's work on
evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
. An example of a 20th-century comparative anatomist is Victor Negus, who worked on the structure and evolution of the larynx. Until the advent of genetic techniques like
DNA sequencing DNA sequencing is the process of determining the nucleic acid sequence – the order of nucleotides in DNA. It includes any method or technology that is used to determine the order of the four bases: adenine, guanine, cytosine, and thymine. T ...
, comparative anatomy together with
embryology Embryology (from Greek ἔμβρυον, ''embryon'', "the unborn, embryo"; and -λογία, '' -logia'') is the branch of animal biology that studies the prenatal development of gametes (sex cells), fertilization, and development of embr ...
were the primary tools for understanding
phylogeny A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological s ...
, as exemplified by the work of Alfred Romer.


Concepts

Two major concepts of comparative anatomy are: #
Homologous structures In biology, homology is similarity due to shared ancestry between a pair of structures or genes in different taxa. A common example of homologous structures is the forelimbs of vertebrates, where the wings of bats and birds, the arms of pri ...
- structures (body parts/anatomy) which are similar in different species because the species have common descent and have evolved, usually divergently, from a shared ancestor. They may or may not perform the same function. An example is the forelimb structure shared by cats and whales. # Analogous structures - structures similar in different organisms because, in
convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...
, they evolved in a ''similar environment'', rather than were inherited from a recent common ancestor. They usually serve the same or similar purposes. An example is the streamlined torpedo body shape of
porpoise Porpoises are a group of fully aquatic marine mammals, all of which are classified under the family Phocoenidae, parvorder Odontoceti (toothed whales). Although similar in appearance to dolphins, they are more closely related to narwhals a ...
s and
shark Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachi ...
s. So even though they evolved from different ancestors, porpoises and sharks developed analogous structures as a result of their evolution in the same aquatic environment. This is known as a homoplasy.


Uses

Comparative anatomy has long served as evidence for evolution, now joined in that role by
comparative genomics Comparative genomics is a field of biological research in which the genomic features of different organisms are compared. The genomic features may include the DNA sequence, genes, gene order, regulatory sequences, and other genomic structural ...
; it indicates that organisms share a common ancestor. It also assists scientists in classifying organisms based on similar characteristics of their anatomical structures. A common example of comparative anatomy is the similar bone structures in forelimbs of cats, whales, bats, and humans. All of these appendages consist of the same basic parts; yet, they serve completely different functions. The skeletal parts which form a structure used for swimming, such as a fin, would not be ideal to form a wing, which is better-suited for flight. One explanation for the forelimbs' similar composition is descent with modification. Through random mutations and natural selection, each organism's anatomical structures gradually adapted to suit their respective habitats. The rules for development of ''special'' characteristics which differ significantly from general homology were listed by Karl Ernst von Baer as the laws now named after him.


See also

*
Cladistics Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups (" clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived cha ...
*
Comparative physiology Comparative physiology is a subdiscipline of physiology that studies and exploits the diversity of functional characteristics of various kinds of organisms. It is closely related to evolutionary physiology and environmental physiology. Many uni ...
* Evolutionary developmental biology *
Phylogenetics In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups ...
*
Transcendental anatomy Transcendental anatomy, also known as philosophical anatomy, was a form of comparative anatomy that sought to find ideal patterns and structures common to all organisms in nature. The term originated from naturalist philosophy in the German provin ...
* Outline of human anatomy *
Anatomical model An anatomical model is a three-dimensional representation of human or animal anatomy, used for medical and biological education. Model specs The model may show the anatomy partially dissected, or have removable parts allowing the student to re ...


References


Further reading

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External links

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