Re: First Family and AAT

H. M. Hubey (hubey@pegasus.montclair.edu)
25 Sep 1995 18:41:38 -0400

szpltdwn@dale.ucdavis.edu (Gerrell Drawhorn) writes:
> 2) Bipedal adaptations in early hominids appear to be mechanically
> designed to deal with increasing gravitational forces applied to the hip,
> hindlimbs and foot. Swimming would seem to completely release the
> hindlimbs from these verticle forces - selection would take the climbing
> foot, ankle and leg of an ancestral hominoid on an opposite trajectory
> than ultimately attained in hominids. Even wading by a quadruped would
> reduce these forces to some degree.

This sounds interesting. Can you please explain the "mechanical
design" whose purpose seems to be to deal with "increasing
gravitational forces." It's obvious that less gravitational
forces would act on the hip in water than if the weight
was being supported on two legs on land, but the other effects?

> I find it difficult to envisage a situation where the lateral
> system in the pelvic musculature, the increased surface areas and
>angulation of the knees, the development of the longitudinal and
>transverse arches of the foot, etc. could arise if animals were in an
>environment where they were buoyant. Either a lightly-built knuckle-walking
>or (more generalized) brachiator (not as specialized as hylobatines)
>would seem to provide a better progenitor than an aquatic form.

It seems that some of these changes could have occured even earlier.
In most quadripeds the the bend at the knees is in the opposite direction
from humans; and the primates seem to be already close to human. What
could have caused this change? If we look at slowly changing from
one angle (most animals) to primates, somewhere in the middle of
evolution the whole leg would have to rotate 180 degrees and have
the legs face outwards or inwards, practically making the animals
lame. Is this explained by any theory, other than one that
begs for catastrophic changes (i.e. punctuated equilibrium) without
really explaining anything. Maybe they didn't need their legs at all
during this time.

But going directly from ape to human can't answer why the legs
became long and powerful. AAT does. The lengthening seems natural
in water and even tallness in general seems to be rewarded in that
environment.

> 3) Many of the soft-anatomical features cited by the AAT proponents
>of an aquatic past are found in related hominoids and cercopithecoids.
> Digital webbing is found in siamangs (hence the name Symphalangus
>syndactylus), gorillas and bonobos.These are probably adaptations to the
>brachiatory hand of hominoids. I suspect the diving reflex, and many
>other AAT traits would also be found in our near relatives. The fact that
> Japanese macaques, Nasalis, and swamp monkeys (C. mitis) are capable of
>swimming suggests a broader capability not restricted to humans. If so,
>there may be many traits attributed as derived from a human AA phase
>that are clearly "pre-adaptations" from an earlier set of features. Until
>we know what the distribution of these characters are in hominoids (ie.
>can it clearly be stated that no other hominoid except humans has a
>"diving reflex"), these characters should be given very low weight in any
>argument.

This still doesn't kill AAT but only asks for a modification and
may even answer some questions.

We already have seen that polar bears are 'aquatic' and
haven't lost their hair. Ditto for the other furry little creature
whose name I just can't recall. Note that bears are more
bipedal than dogs or cats.

so maybe the primates were also aquatic at one time but came
out of it and went back to the trees and one of the species
stayed in this habitat a lot longer.

So then we have yet another reason for why the digits got
longer so that grasping became possible. If the digits got
longer (and got webbed) in response to the aquatic environment,
then when they came out of the water, they would have had an
easier time grasping things than say cats, or dogs. Come to
think of it even bears seem to have bigger rear feet than
cats/dogs! Maybe bears are descended from an earlier line of
which the polar bear is the one that still inhabits the same
habitat and has thus kept its webbing.

-- 



Regards, Mark



http://www.smns.montclair.edu/~hubey