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Re: Feduccia discussions



In a message dated 96-09-25 17:11:03 EDT, JNorton@MAILBOX.UNE.EDU writes:

> The idea I have suggested above would apply to an animal that needs
> control on the way down to its prey, and lift to get back up to its
> perch.  Lift and control could co-evolve in the forelimb, and the
> hindlimb could make the transition from a cursorial configuration to
> a grasping one simultaneously.
> 
> Reactions from the group?

The insurmountable problems with ground-upward hypotheses for the origin of
avian flight are gravity and time. The evolution of flight requires time:
specialized structures such as perching feet, avian wing, and so forth cannot
arise overnight. It takes millions of years for the random walk of evolution
to alight on the right combinations of characters to build a flying
vertebrate, even when the vertebrate is already involved in a lifestyle or
milieu, such as dwelling in trees, that might abet the evolution of flight.
If in addition to this, natural selection is called upon to evolve structures
that must carry the creature off the ground against gravity, the probability
of hitting on the right character combinations to do so decreases
astronomically.

For example, one can devise scenarios for the ground-up evolution of flight
as an aid to predation. But there are so many easier improvements to a
predatory lifestyle that could evolve, and in a much shorter time frame, that
they swamp all the "difficult" evolutionary improvements.

The evolution of powered flight as the ultimate solution to the falling
problem in a habitually arboreal or acronomic lifestyle proceeds much more
naturally and compellingly than any ground-upward scheme I've encountered.