Re: AAT Theory

David L Burkhead (
29 Sep 1995 20:36:35 GMT

In article <44f06b$> (Sean Stinson) writes:
>David L Burkhead ( wrote:
>: In article <> (H. M. Hubey) writes:
>: > (David L Burkhead ) writes:
>: >
>: Again with the streamlined. That's a _claim_, not a "fact."
>: Furthermore, it's a claim that does _not_ fit the conclusion of a
>: "wading ape." In fact, a hairy body would have _less_ drag for that
>: upright wading ape. Go look up turbulent vs laminar flow separation
>: drag in bluff bodies. (This kind of thing is one of the reasons the
>: "obvious" is so often wrong.)
>Just a small note here:
> Last time I checked ALL olympic swimmers shave their legs and
>body. Then they put rubber swimming caps on their heads to cover the
>hair on their heads. It seems to me that if you want to know about moving
>quickly through the water you should ask an olympic swimmer about it.
>I don't think you'd find any that suggest remaining unshaven.
> Turbulent flow may work for wading creatures, but who says that
>we remained wading throughout this entire evolutionary process?
>Last time I checked nobody was suggesting that we are the biological
>equivalent of a golf ball.

Go look at the AAH again. It postulates a _wading_ ape. The
critical factors being argued in this particular thread (long legs,
upright posture, changes in pelvic structure, etc.) are supposed to be
the result of wading. The claim that long legs would have let us move
out to deeper water to escape land predators only applies if we are

There are arguments wrt a swimming ape, but that's not what I'm
discussing here. And the experience of Olympic atheletes is just not
relevant in _this_ thread because there is no Olympic _wading_
competition. Limb speed (kick and arm stroke) and characteristic
length (horizontal vs vertical orientation) are both greater in
swimming than in wading, leading to higher Re. This means you'll get
your turbulent transition before the separation point anyway. Under
those circumstances you'll want to delay turbulent transition as long
as possible (so long as it happens before flow separation) so as to
minimize boundary layer drag.

Note also the difference in times between shaved/unshaved in
swimming times. It comes to a small fraction of a second over most
race distances. That may be significant in world class competitions,
which are decided by that fraction of a second, but it's a relatively
minor factor. Other areas (like foot shape, body proporitions, hand
size, etc.) have far more effect for far smaller changes. Why, then,
were _they_ not selected for in the case of a "swimming ape"?

David L. Burkhead

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