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RE: Arboreal Theropods: The prize at the bottom of the cracker jack box

Several messages by GSP seem not to have reached me. Were they offlist?

Gesendet: Donnerstag, 18. Juli 2013 um 15:12 Uhr
Von: "Jason Brougham" <jaseb@amnh.org>

> Evolution does not, actually, act on "a need". Humans have a need for better 
> birth morphology to improve maternal chances of survival, but it never arose.

Bad example. Women's average hip width is a compromise: wider hips would make 
birth easier to survive for all involved parties, but they'd also make walking 
more difficult (if nothing else more costly).

It's true that evolution doesn't act on a need, mutations happen at random and 
not because they're needed, selection works on what's there and not what might 
happen in the future; but cases where a beneficial mutation seems not to have 
happened commonly turn out to be compromises between selection pressures in 
different directions.