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Re: Big-brained birds evolve faster



I'm curious: could the same thing be said about forelimb morphology? I would think that most would say "Of course the wings of birds allowed them to enter niches unavailable to other organisms, leading to greater diversity." If this is true, why is the same claim for large brains more controversial?

Well, for starters, I'm not sure I'd agree with the wings statement: wings should promote survivorship, which promotes range expansion and population size. While this can produce high diversity simply by promoting interactions with new environments (via mobility), I would argue that it is variation in wing structure that is more likely to promote diversity. There are particular flight dynamics that seem to generate species diversity most readily (specifically, those planforms and behavioral guilds that promote isolation).


In any case, part of the problem is that the actual effect of a large brain is a bit more fuzzy, as is the source of selection for large brains. I'm not so much skeptical of the result that diversity and brain size can go together for certain groups, but more that this must involve a cognitive effect. It could just as easily be sensory and control related (though cognitive ability is certainly plausible, too).

Cheers,

--Mike


Michael Habib, M.S. PhD. Candidate Center for Functional Anatomy and Evolution Johns Hopkins School of Medicine 1830 E. Monument Street Baltimore, MD 21205 (443) 280-0181 habib@jhmi.edu