Re: Campbell's even crazier than a MANIAC? (archeopteryx climbing)

[Michael Habib <mhabib5@jhmi.edu>]

don ohmes wrote:

> I already pointed out the error, which is failing to consider the 
> various points of various glide sequences at which selection on 
> incipient flapping can occur. Nothing to do w/ falsifying equations.

That's the different issue from the one which I was addressing.  The 
point was simply that the required set of ancestral traits for arboreal 
flight origins may be more strict than it appears.  Or, to be more 
specific - assuming that bats did indeed have gliding ancestors, it is 
still quite likely that living gliders (like flying squirrels and 
possums) are not good analogs, in part because the gliding mode and 
planform of animals like flying squirrels produce mechanical 
limitations to flapping.

> I know of no successful attempt to falsify either route, including the 
> current "bird evolution cannot be gravity-driven because they are not 
> purely arboreal in origin" attempt, which is itself falsified by the 
> fact that early birds could have readily utilized trees in the way I 
> describe.
>
> I tried to falsify arboreal origin years ago, and failed. Ditto 
> ground-up. Concluded it couldn't be done ("way too hard"), and am very 
> skeptical of claims to the contrary. It is all 'best guess', afaik. 
> But it is fun to falsify the attempts to "solve" the mystery.

It's better than best guess, but not definitive, either.  The evidence 
that we have for birds indicates a strong terrestrial component to 
flight origins.  That does not eliminate any possible arboreal 
component, but it does contrast with bats, for which evidence suggests 
a strong arboreal component.  This difference appears, as best we can 
tell, to be real and notable.  To that extent, the various models are 
testable.  More specific scenarios, while fun, are largely speculative 
and probably not very informative.  Especially if they try to make 
assumptions about the magnitude of selection coefficients (estimating 
sign is a bit more reasonable).

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