24 February 2010

What is the purpose and significance of comparative anatomy?

I am continuing to read F.J. Cole's History of Comparative Anatomy from Aristotle to the Eighteenth Century. While discussing the work of the 16th century anatomist Volcher Coiter, Cole first notes that Coiter compared the human skeleton with that of several other vertebrates and then presents a one-sentence criticism of his philosophy:

[Coiter] emphasizes, however, points of difference rather than homologies, and has therefore not fully grasped the purpose and significance of the comparative method.
From this we can deduce that according to Cole, the purpose and significance of comparative anatomy is to find anatomical homologies between different species.

A homology, or a homologous organ, is an organ that is similar in structure and position (but not necessarily in function) in 2 or more organisms and, which was inherited from a common ancestor.

Earlier in the book, Cole mentions, again in passing, while summarizing the similarities Pierre Belon noted between different bones of birds, an important caveat about the determinations of homologies:
[Belon] had no knowledge of the development of the skeleton, from which alone is it possible to homologize accurately the bones of the wing and the leg in birds.
To summarize, comparative anatomy gives clues about which organs may be homologous between different species (or within the body of one animal), but only by comparative embryology and development can we be sure of their homology.

This is one thing I like about the structure Cole's book: tidbits of significant insight scattered among biographical data or anatomical discourse.

No comments: