Re: Bipedalism and other factors
Pat Dooley (patdooley@aol.com)
2 Jul 1995 21:26:05 -0400
herwin@osf1.gmu.edu (HARRY R. ERWIN) wrote (in part):
>It's easy to envision early hominids having some skill with water (i.e.,
>behavioral adaptation), but without a great deal of skeletal adaptation
in
>that direction. Look at cats--tigers take to the water easily, while most
>species avoid it. I suspect this can be tabled as having no strong
>evidence in either direction. In any case, hominids probably did not
>spend most of their time in the water. Not with limbs adapted to climbing
>and bridging.
Jaguars take to the water even better than tigers. They collect a
substantial
proportion of their prey from water. However, neither they, nor any other
primates, has the ability to dive to any depth.
The upper limit on unassisted human diving performance
is about 250 feet. Some human groups regularly dive to a depth of 80
feet. These aren't just learned capabilities - there are physiological
adaptations to support them, including conscious control over
breathing, a heightened diving reflex that slows the heart rate
down from 72 to 35 beats per minute, and an ability to hold ones
breath for 3 minutes or more.
Such features would not be surprising if our closest relatives
could achieve some significant fraction of these capabilities.
But, there is no sign of such capabilities in them or in other
fully terrestrial mammals.
It can also be argued that human limbs are partially adapted for
swimming and diving. In particular, a human being can swim or dive with
their arms, legs, head and body in a plane. That improves efficiency
and is a feature of most semi-aquatic and aquatic mammals.
There is also the issue of residual webbing in humans. That useless
flap of skin between your thumb and forefinger is the only thing
that restricts the movement of your thumb back another thirty degrees;
other apes don't have such a flap. A significant percentage of humans
still
have further vestigal webbing between their fingers and toes.
Pat Dooley
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