Re: Convergent traits... was Re: AAT Theory
Thomas Clarke (clarke@acme.ist.ucf.edu)
14 Oct 1995 13:12:40 GMT
In article <60.3285.7295.0N1F8B27@canrem.com> writes:
> TC> >Apart from that,as far I know their is no evolutionary law
> TC> >that
> TC> >states that a "good trick" discovered by one species will also be hit
> TC> >upon by another.
> TC> No law of course, only the observation of the convergent evolution of
> TC> similar traits to fill similar niches in vastly different species and
> TC> locales.
> Like those convergent traits seen among all aquatic marine
> mammals: smaller or non-existent ears; shorter or non-existent
> limbs; extremely large, heavily lobulated kidneys; and young that
> are born quite advanced compared to similar terrestrial mammals
> (for example, seals as opposed to land-based carnivores), or
> which grow very quickly, or both. We have none of these traits,
> and as far as our young are concerned, we've changed in the
> opposite direction from all aquatic marine mammals. Why are
> humans so conspiciously the odd man out in all these ubiquitous
> convergent traits?
Round and round we go. Like the "land origin" ideas which have
undegone quite a bit of modification since Darwin's time in light
of fossile finds, the "aquatic" ideas have undergone modification.
Considering the available fossil evidence, the available time for
an aquatic or littoral or other water-related episode has been
narrowed to 6MYA to 4.5MYA (but has not been eliminated).
Thus at most 25% of the time since divergence since the Miocene apes
was spent in an environment that favored aquatic adaptations.
It is not suprising that only vestiges of this episode remain and
that they have been overlain by many later adaptations such as
altricial infants.
Thus humans are the odd man out because they took a step into the
water and then retreated three steps back.
Ian Tattersall in the "The Fossil Trail" points out the origin of
bipedalism as the key problem. Was it environmentally driven,
behaviorally driven or what? I really think the environmental
ideas behind the AAT have something to offer.
Tom Clarke
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