John K Clark (johnkc@well.com)
Sat, 25 Jan 1997 08:03:48 -0800 (PST)


CurtAdams@aol.com On Fri, 24 Jan 1997 Wrote:

>Bipedalism is a mystery, but all the apes have excellent hands.
>Opposable thumbs allow a nice secure grasp on a tree branch.
>[...] Hominids didn't gain hands, they lost them, going from 4 to 2.

A Chimpanzee's hand is very dexterous by animal standards but not by human
ones. A chimp still spends most of it's time walking on 4 legs so the hand
must be optimized for locomotion. A chimp does have an opposable thumb of
sorts, but is very short and stubby and the fingers are quite long and that
makes things clumsy. Even more important, in a human the thumb is twisted
90 degrees to the plane of the other fingers, so the hand does not work very
well for walking but works great for precision gripping, placing the thumb
against one of the fingers.

3.9 million years ago Lucy had a hand that was FAR more human than the hand
of any ape living today and was almost as good as our own. Lucy's hand did
contain one puzzling flaw, the muscles at the base of her thumb must have
been small, so although her precision gripping was excellent, her power grip,
the placing of the thumb against the entire hand, was weak. Lucy could not
climb trees as well as we can.

Everybody always assumed that the power grip came first and the precision
grip much latter, and I don't blame them for assuming that, it's very logical,
but that's not what happened. As in History, proving that something is
logical in Evolution is not enough to prove that it happened.

John K Clark johnkc@well.com

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