Re: Bipedalism and other factors
Clara N. Fitzgerald (cfitzger@s.psych.uiuc.edu)
16 Jul 1995 02:43:41 GMT
patdooley@aol.com (Pat Dooley) writes:
>Re: Bipedalism and other factors
>>From: herwin@gmu.edu (Harry Erwin)
>
>>> 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.
>>
>>The thumb/first-finger web is the primary path by which large external
>>forces are coupled to the hand structure in man.In the apes,the thumb is
>>reduced or(in the gibbons)adapted to swing out of the way and the forces
>>are transmitted via the fingers, which are vulnerable to breakage and
>>other injury and so must be fairly tough and indelicate. Yes, the web
>>restricts thumb mobility, but it allows the thumb and fingers to be
>>delicate manipulatory appendages with a reduced risk of damage.
(I seem to remember a genetically transmitted variation in angle
of thumb movement; some portion (I can't recall my 8th grade biology
course figures right now) of the population has 'hitch-hiker's thumb',
probably about a 10 degree difference)
What exactly do each of you mean by the 'web'? There is some underlying
muscle, which allows a precision grip and probably enhances a power grip,
and there is a loose flap of skin which prevents the thumb from bending
very far from the hand. The skin flap is considerably larger than the
muscle boundaries.
>>--
>>Harry Erwin
>Pat Dooley
--
-Clara A. N. Fitzgerald cfitzger@s.psych.uiuc.edu
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