Re: AAT

Harry Erwin (herwin@gmu.edu)
Wed, 05 Jul 1995 22:48:27 -0400

I note that Ralph Holloway suggests there is some value to our arguing out
the aquatic ape theory, given that working anthropologists tend to roll
their eyes when asked about it.

I've been thinking about this issue in my subconscious for a month or more
now, trying to define a quantitative test equivalent to the parsimony
argument that Holloway cites. The problem is a basic lack of data on
primate adaptations to an aquatic environment. The fossil data consist of
an extinct Malagasy lemur (Paleopropithecus) that had some features that
_could_ be interpreted as aquatic in nature, but most of whose features
are more consistent with an orang-like life-style, and some fossils from
swamps, the most important being Oreopithecus. Now Oreopithecus is
interesting--it's adapted to a swamp environment by being about as
arboreal as Hylobates. (BTW, hylobatid brachiation seems to be extremely
efficient for short-range movement above the ground but hardly useful for
longer-range movements.) 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. 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. 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. 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.

I think that's the gist of what would be the average anthropologist's take
on the subject.

-- 

Harry Erwin

Internet: herwin@gmu.edu

Home Page: http://osf1.gmu.edu/~herwin (try again if necessary)

PhD student in comp neurosci: "Glitches happen" & "Meaning is emotional"