Re: Big-brained birds evolve faster

[Mike Habib <habib@jhmi.edu>]

> 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