Re: AAT
Pat Dooley (patdooley@aol.com)
9 Jul 1995 19:51:51 -0400
Harry Erwin writes:
<< Deletions>>
> That sort of tells us that apes usually have
>dealt with water by staying out of it.
>
>Now the major problem with the aquatic ape hypothesis is that it involves
>two sequential adaptive stages, each rather major in a behavioral sense,
>the first into the water and the second out of it, within the period 7-4
>MYr BP.
The first stage - into the water - took up most of the 7-4 Myr BP. The
end result of that period is a fully bipedal ape partially adapted for
an aquatic existence.
The second stage covers the last 4 million years when humans
became fully adapted for a terrestrial environment. The non-harmful
aquatic adaptations remain with us.
>We do have some data on rates of evolution. Generally, a primate
>species lasts about 1 MYr, so we're talking about three species worth of
>evolution. Now evolution does go faster, but in the context of an
>explosive radiation (no evidence) or an externally applied selective
>gradient.
The first stage roughly corresponds to the geological evidence for
the Sea of Afar. What sort of selective gradient would the sudden
formation of a large sea impose on those creatures trapped on islands
in that new sea? Fairly drastic, one would think.
>In the latter case, you get fixation in perhaps 1000 generations
>as the natural variation in the gene pool (better be good sized!) is used
>up, so the initial impetus would not have continued for a significant
>portion of the 3 MYr.
Assuming, of course, that the initial impetus didn't continue. But
the trapped populations would have been under continued evolutionary
pressure as, firstly, the forests on the islands dried out, and secondly,
the
Sea of Afar gradually dried out.
>Instead, evolution after the first 1000 generations
>would have been dependent on the usual evolutionary processes at the
usual
>rates. Also, the rate of evolution could have been expected to regress
>towards the mean, so we're talking of perhaps 4 species in 3 MYr. That's
>probably enough to evolve bipedality in a small African ape, but hardly
>enough to take it out to sea and return.
>
Adaptations do not necessarily evolve in sequence. If there was time
enough
for a major change like bipedalism, there was certainly enough time for
the
rest of the AAT adaptions to evolve in parallel, particularly if, as would
be
the case in an aquatic scenario, the adaptations were complementary.
>
>I think that's the gist of what would be the average anthropologist's
take
>on the subject.
I'll believe 'em when they dig up the fossils to prove humans evolved far
away from any sea shore. The fossil gap is still there but the plugging
seems to be drifting closer to the ancient Sea of Afar.
Pat Dooley
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