Re: Bipedalism and other factors
Phil Nicholls (pnich@globalone.net)
Tue, 11 Jul 1995 05:21:36 GMT
patdooley@aol.com (Pat Dooley) wrote:
>Re: Bipedalism and other factors
>>From: herwin@gmu.edu (Harry Erwin)
>
>I wrote:
> >> 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.
>>
>>These are features that could have been acquired fairly late, especially
>>since they are nervous system adaptations, an area where biological
>>innovations are known to be particularly easy. Fixation would have taken
>>no more than 1000 generations. My suspicion is that the connection of the
>>emergence of modern man with the appearence of sea-going cultures might
>be
>>related.
>The human diving reflex is more than a simple nervous system adaptation.
>For example, in simulated deep dives under laboratory conditions it was
>found that the circulation to the limbs was completely shut down and
>the heart rate slowed to about 12 beats per minute.
As has been posted several times before, the "human" diving reflex is
also present in dogs and any other mammal that you can train to dive
and thus remove the fear such an activity would otherwise entail.
Check "Aquatic Ape: Fact or Fiction."
>Other unique adaptations that facilitate human diving include:
>1 .Hairlessness ( to reduce drag on descent and ascent)
I believe there are studies that show that it actually makes no
difference.
>2. Downward pointing nostrils (that stops water from being forced into the
>nasal cavaties)
The direction of human nostrils is a result of (a) being catarrhine
primates and (b) lose of facial prognathism. Early hominids did not
have noses like ours.
>3. Descended larynx
The neandertal larynx is only partially descended compared to our own.
More importantly, newborn infants do not have a descended larynx.
>4. Bipedalism (keeps legs, spine and head in one plane)
There are no aquatic bipeds.
==========================================================
Phil Nicholls "To ask a question you must first
pnich@globalone.net know most of the answer.
Semper Alouatta! - Robert Sheckley
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