Re: Origin of feathers

[Dinogeorge <Dinogeorge@aol.com>]

In a message dated 98-04-08 23:45:33 EDT, swo@execpc.com writes:

<< The "behavior evolve first" hypothesis is one of the main tenets of
 modern zoology. And it is not always untestable! In this case, yes, I
 agree, it is hard to test. >>

To confirm this hypothesis in any particular case, you would have to be able
to observe the behavior prior to the appearance of the feature in question,
follow the evolution of the population through the appearance of the feature,
and then observe the behavior after the appearance of the feature. This is
presently impossible to do. Thus we are left with sequences of inferences that
may seem plausible but for which there is no empirical evidence. I can
certainly imagine circumstances in which the evolution of a feature would
evoke a behavior that was absent prior to the feature's appearance.

In constructing an evolutionary scenario (since we cannot go back in time and
observe populations of organisms evolve), it is necessary to provide a
plausible, compelling cause for each step in the scenario. "For display" or
(even more remote) "for flight" are simply not compelling reasons for the
initial appearance of pre-feathers, because they stem from characteristics of
the behavior of the organism that can only be known after the evolution of
pre-feathers, not before. You are using the future to compel the past. But if
you say that pre-feathers evolved as a mechanism for sulfur excretion, you
have provided a compelling reason for their appearance. The cause--the >reason
for the initial appearance< of the pre-feathers--here lies >before< their
appearance, not after.

Another example: Say that a lineage of small animals, previously accustomed to
a ground-dwelling lifestyle, becomes arboreal. Two causes are postulated: (1)
the animals went into the trees to escape ground-dwelling predators; (2) the
animals went into the trees to find food. Which of these is the more
compelling? (Here I'm not concerned with the >real< reason, just in choosing
between the two proferred reasons.) I assert that (1) is more compelling,
because the danger from ground-dwelling predators exists prior to the arboreal
lifestyle, whereas the availability of food in the trees cannot be known to
the animals until they go up there and find it. Hypothesis (2) is an example
of the future compelling the past, and should be rejected.

Once the animals get into the trees, perhaps the presence of a good food
supply helps compel them to stay there, but it could not have gotten them up
there in the first place.