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Re: Campbell's even crazier than a MANIAC? (archeopteryx climbing)
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
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).
Michael Habib, M.S.
Center for Functional Anatomy and Evolution
Johns Hopkins School of Medicine
1830 E. Monument Street
Baltimore, MD 21205
(443) 280 0181