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Comparative anatomy

From Wikipedia, the free encyclopedia

Comparative anatomy studies similarities and differences in organisms. The image shows homologous bones in the upper limb of various vertebrates.
Comparative anatomy studies similarities and differences in organisms. The image shows homologous bones in the upper limb of various vertebrates.

Comparative anatomy is the study of similarities and differences in the anatomy of different species. It is closely related to evolutionary biology and phylogeny[1] (the evolution of species).

The science began in the classical era, continuing in Early Modern times with work by Pierre Belon who noted the similarities of the skeletons of birds and humans.

Comparative anatomy has provided evidence of common descent, and has assisted in the classification of animals.

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  • ✪ Comparative Anatomy: What Makes Us Animals - Crash Course Biology #21
  • ✪ Comparative Anatomy as Evidence of Evolution
  • ✪ CARTA: Bipedalism and Human Origins-Comparative Anatomy from Australopithecus to Gorillas
  • ✪ Comparative Anatomy Introduction
  • ✪ Homologous Structures vs Analogous Structures | Key Differences


Hi, I want you to meet my friend Shoshanna. She's a Zebra Finch and she is very good at it. She's here to help me talk about comparative anatomy, which is the study of similarities and differences between the anatomies of animals. We study comparative anatomy because it helps us learn more about our evolution and our shared ancestry. Organisms have their evolutionary history written all over them, if you know what to look for. For instance, which of these two living organisms would you say I'm more closely related to? Shoshanna the finch? Or Gordon the plant? This isn't a quiz, but.... Sure, it is a quiz. It is the easiest quiz that you will ever take in your life. Gordon is green and can make his own food with just sunlight, water and carbon dioxide. While Shoshanna can't make her own food, she has to move around to find stuff to eat, escape predators, find mates and poop on park benches. Just like me...except, not the pooping on park benches, I mean the moving around. So yeah, shocker, I am more closely related to a bird than to a plant. You get a gold star. So that one's obvious, but as the relationships between organisms get closer, the questions get a lot more interesting. So what IS an animal? I mean, I know you know what an animal is, but when you're looking at Shoshanna and me here, what clues you in to the fact that we are members of the kingdom Animalia? Two things: For starters, we're both moving. Locomotion is a really good sign that an organism is an animal, unless you're a sponge. Now, I know what you're thinking though: Protists, bacteria and archaea move around using flagella and cilia. But they also only have one cell. It's the multi-cellular locomotion that's so peculiar and specific to animals. So animals move because of the second trait that we have in common: We're heterotrophs. We get our energy from eating other life forms. Locomotion also helps us avoid predation and seek out mates for reproduction. Plants can mate by dispersing their seed to the wind or having an insect come by and fertilize them. But if land animals did that? Things would get like, really messy and gross. Some aquatic animals actually do just release their sex cells into their surroundings and cross their fingers and presumably close their mouths, and hope that somebody gets pregnant. So, since animals have to eat and move around, they've evolved anatomical forms that help them do those things. But obviously those forms aren't the same on all animals. For instance, in order to move, Shoshanna and I both have to be able to apply force to the ground or the air to propel ourselves. Here's me pushing off the ground with my feet. And now, here's Shoshanna applying force to the air with her wings, which keeps her afloat and moving. And if I had a shark in the studio with me, which thankfully I do not, so I'll just pretend to be a shark, my fins would apply force to the water, which would propel me forward. Now, you have to be careful with this stuff, because even though similar body structures, like fins or wings or feet, can mean animals have a close common ancestor, it can also mean the animals just evolved similar forms just because that's the best structure for the job. When this happens, it's called convergent evolution. For example, a tuna, a penguin and a seal are all animals that spend all or a lot of their time in the water. One's a fish, one's a bird and one's a mammal, but all three of them have a suite of similar features, the most notable being a really sleek, fusiform body that can move through the water like nobody's business and fins for propelling those bodies. But of course those three animals have very different evolutionary origins. Each of these three marine animals have independently "converged" on similar body shapes because they live in the same environment and need to do the same sorts of things. So instances of convergent evolution can make linking physical structure of an animal to its evolutionary history a little bit tricky. Which is why, for a long time, nobody really put much stock in comparative anatomy as proof as evolution. That is, until Thomas Henry Huxley came along. [BIOLO-GRAPHY] Thomas Henry Huxley was the Father of Comparative Anatomy and the Father of Modern Paleontology. And he invented the word "agnostic" to describe his spiritual views. And he was the first person to conclude that birds evolved from small carnivorous dinosaurs! Phew! I'm glad I'm sitting down for this. Plus, we have much respect for his facial hair. Huxley was born in England in 1825, and though he started out as a doctor, after serving as a ship surgeon on a voyage to Australia in his 20s, he took to studying marine invertebrates. During his voyage, he sent all his papers back to England, and when he got home he found that he had become a kinda famous marine invertebrate expert and he was admitted into the Royal Society. Huxley made friends with other hot-shot natural scientists, including Charles Darwin, and a few years later, when Darwin outlined his theory of evolution in On the Origin of Species, Huxley is reported to have said, "How extremely stupid not to have thought of that!" In fact, he became such a huge Darwin supporter, that everybody started calling him "Darwin's Bulldog" because he threatened to cut the fool who badmouthed evolution. This is a good one: Huxley said, when talking about On the Origin of Species, "Old ladies, of both sexes, consider it a decidedly dangerous book." You just got Huxslapped. With this new tool of the theory of evolution, and in part to help promote the theory of evolution, Huxley connected paleontology and biology together by looking for similarities in anatomy in the fossil record, where he found all kinds of interesting stuff. Like some really obvious similarities between prehistoric horse fossils and modern day horses, as well as between dinosaurs and birds, though nobody really bought his insights into the resemblance between birds and dinosaurs for another hundred years. And just in case you were still on the fence as to whether intelligence is heritable, Thomas Henry Huxley is the grandfather of Brave New World writer Aldous Huxley and of Sir Andrew Huxley, who won the Nobel Prize for Physiology or Medicine in 1963. Because all animals come from the same evolutionary origin, in addition to sharing some anatomical structures like Huxley studied, we're also built from the same rudimentary blueprint. Our cells work pretty much the same no matter what sort of animal we are. So while animals have different strategies for moving around and acquiring food, once the food is gotten, all animals break it down, turn it into useful energy, distribute nutrients, and eliminate waste in pretty similar ways, unless you're a sponge. Each of those functions is performed by collections of cells that group together in the body to form tissues. There are 4 primary tissue types in the human body: epithelial tissue, connective tissue, muscle tissue and nerve tissue. Epithelial tissue is formed by cells that bind very closely together. A layer of it covers every organ and lines the digestive tract to prevent crazy acids and poop and stuff from going where it's not supposed to go. Epithelial tissue can also produce the slippery fluid to let your organs slide over each other like the membrane that lines the inside of your ribs so that your inflating lungs don't build up friction as they expand. Most types of connective tissue are made up of fibrous strands of collagen protein, and it adds support and structure to your body and holds your parts together. Some examples of connective tissue include the inner layers of your skin, your tendons, ligaments, cartilage, and bone. But oddly enough, connective tissue isn't defined by it's ability to connect, but instead by the presence of an extra-cellular matrix, meaning that part of the tissue extends outside of cell. And so, somewhat confusingly, blood and fat are also considered connective tissues. Muscle tissue is made up mostly of two specialized proteins: actin and myosin, which can slide past one another and allow for movement. It also includes a bunch of other proteins, including that longest word-in-the-world one, titin. And finally, there's nerve tissue, which generates and conducts electrical signals in the body. These electrical messages are managed by the nerve tissue in the brain and transmitted down the spinal cord to the rest of the body. Nerve tissue is made up of two types of cells the neurons, which do the electrical work, and the glial cells, which insulate and support the neurons. These tissues are then organized into organs, which perform different functions in the body, and these organs work together in organ systems. For instance, most animals have a digestive system made up of a mouth and an esophagus and a stomach and intestines and an anus. And a lot of animals have a skeletal system made up of bones, tendons, ligaments and cartilage. We're going to be talking about each of these systems in a lot more detail in a few weeks. These organ systems, like many different kinds of anatomical structures, are shared by lots of different kinds of organisms, unless you're a sponge. Because about 1.6 billion years ago, an organism developed that had a digestive system and a muscular system, and suddenly that organism was in it to win it. That organism was the common ancestor for all animals today, and it's the reason me and Shoshanna here are gonna hang out at the animal family reunion. Thank you for watching this episode of Crash Course Biology. If you want to check out any of the stuff we talked about, there's a table of contents over on the side. Or you can just re-watch the whole video and we'll love you extra much. If you have any questions for us, please leave them in the comments below or you can get in touch with us on Facebook or Twitter. We'll see you next time.



Skeletons of humans and birds compared by Pierre Belon, 1555.
Skeletons of humans and birds compared by Pierre Belon, 1555.

The first specifically anatomical investigation separate from a surgical or medical procedure is associated by early commentators with Alcmaeon of Croton.[2] Pierre Belon, a French naturalist born in 1517, conducted research and held discussions on dolphin embryos as well as the comparisons between the skeletons of birds to the skeletons of humans. His research led to modern comparative anatomy.[3]

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 oxen. 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.[4]

A drawing by Edward Tyson
A drawing by Edward Tyson

Edward Tyson is regarded as the founder of modern comparative anatomy. He is credited with determining that whales and dolphins are, in fact, mammals. Also, he concluded that chimpanzees 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's work on evolution. 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, comparative anatomy together with embryology were the primary tools for understanding phylogeny, as exemplified by the work of Alfred Romer.[citation needed]


Two major concepts of comparative anatomy are:

  1. Homologous structures - 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.
  2. Analogous structures - structures similar in different organisms because, in convergent evolution, 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 porpoises and sharks. 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.[5]


Comparative anatomy has long served as evidence for evolution, now joined in that role by comparative genomics;[6] 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.[7] 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


  1. ^ Gaucher, Eric A.; Kratzer, James T.; Randall, Ryan N. (2010). "Deep Phylogeny—How a Tree Can Help Characterize Early Life on Earth". Cold Spring Harbor Perspectives in Biology. 2 (1): a002238. doi:10.1101/cshperspect.a002238. PMC 2827910. PMID 20182607.
  2. ^ Blits, K. C. (1999), Aristotle: Form, function, and comparative anatomy. Anat. Rec., 257: 58–63. doi: 10.1002/(SICI)1097-0185(19990415)257:2<58::AID-AR6>3.0.CO;2-I
  3. ^ Gudger, E. W. (1934). "The Five Great Naturalists of the Sixteenth Century: Belon, Rondelet, Salviani, Gesner and Aldrovandi: A Chapter in the History of Ichthyology". Isis. 22 (1): 21–40. doi:10.1086/346870.
  4. ^ Caldwell, Roy (2006). "Comparative Anatomy: Andreas Vesalius". University of California Museum of Paleontology. Retrieved 2011-02-17.
  5. ^ Kardong, Kenneth V. (2015). Vertebrates: Comparative Anatomy, Function, Evolution. New York: McGraw-Hill Education. pp. 15–16. ISBN 978-0-07-802302-6.
  6. ^ Hardison, R.C. (2003). "Comparative genomics". PLoS Biology. 1 (2): e58. doi:10.1371/journal.pbio.0000058. PMC 261895. PMID 14624258. open access publication – free to read
  7. ^ Campbell, Neil A.; Reece, Jane B. (February 2002). Biology. San Francisco, CA: Benjamin Cummings. pp. 438–439.


  • Löw, Péter et al. (2016). Atlas of Animal Anatomy and Histology. Springer, [1].
  • Wake, M.H. (ed.)(1979). Hyman's Comparative Vertebrate Anatomy. 3rd ed. University of Chicago Press, [2].
  • Zboray, Géza et al. (2010). Atlas of comparative sectional anatomy of 6 invertebrates and 5 vertebrates. Wien: Springer, 295 p., [3].

External links

This page was last edited on 11 January 2019, at 21:07
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