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Re: An alternative to ST and AAT
Phillip Bigelow (bh162@scn.org)
Sat, 16 Nov 1996 19:10:55 -0800
Paul Crowley wrote:
> Primitive retentions are of a quite different nature; they are
> essentially non-functional; selective pressures have little
> effect on them.
Hard evidence shows otherwise.
Primitive character traits are *usually* acted on by selective
pressures; that is why many primitive traits have such a
temporal longevity (they have remained optimum for the operating
environment). Evolution is non-selective in it's
selectivity (no, that is not a typo). By that I mean
that all character traits, primitive and derived alike,
are constantly called up for "review" by the
environment. If old primitive traits pass mustard,
it is likely that there is a lingering need for them, and
these traits will be preserved. "Preservation" in this
context is an active verb; it is by no means passive.
Primitive traits often take an active role in natural
selection.
An example, you ask? Well, consider the Dinosauria.
One plesiomorphic trait of the group is bipedalism.
The plesiomorphic trait of most (but not all) of the ancestral
group to dinosaurs (the crocodiliomorpha) is
quadrupedalism.
But an entire clade of dinosaurs reverted to the primitive
condition of quadrupedalism. Apparently, selective
"pressures" (god, I hate that word, why not "opportunities"?)
made the primitive 4-legged condition more desirable than the
derived bipedal condition.
And then there is the case of the re-appearance of the ossified
dinosaurian furcula (a primitive trait) in some species, long after
it had been selected-out of the earlier dinosaurs (although, in
the earlier dinosaurs, it was probably retained as a
cartilaginous element).
But don't get me started on that.
<pb>
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