RE: organic conversations

[Tim Williams <twilliams_alpha@hotmail.com>]

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 
not."


Cheers

Tim

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