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RE: organic conversations
David Marjanovic wrote:
>> Owen (1834) defined homology as "the same organ under every variety of
>> form and function". [...] Thus, any definition of homology that has an
>> evolutionary component (including 'shared ancestry', which is its current
>> usage) is a re-invention from Owen's original concept.
> That strikes me as exaggerated. It's just an explanation of what on the
> planet "the same organ" _means_. :-)
Yes, but having the "same organ" could be explained by analogy rather than
homology. Only the latter requires a shared ancestry. I know I'm not telling
you anything new here. But the fact remains that our current concept of
'homology' does represent a revision of Owen's original concept, no matter how
sensible that revision was.
>> Molecular biologists recognize that certain genes or proteins have a
>> common ancestry, just as organismal biologists recognize that certain
>> organs or appendages have a common ancestry.
> Yes. They just shouldn't say "% homologous" when they mean "% identical".
> That's all.
Agreed. This is something I've been guilty of on occasion. %-) I like
Fitch's way of expressing it: "It is worth repeating here that homology, like
pregnancy, is indivisible. You either are homologous (pregnant) or you are
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