Re: Bipedalism and other factors

Pat Dooley (
17 Jul 1995 00:27:07 -0400

Subject: Re: Bipedalism and other factors

<< deletions>>

I wrote:

>>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.

Phil Nicholls ( replied:

>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."

No one is denying the existence of the diving reflex in
other mammals. The question to be answered is whether or
not the reflex in humans is out of the range one would
expect for arboreal apes.

If the performance of your diving dogs matched the performance
of humans, I would be impressed. I presume it isn't in the
same league since you have failed to provide any information
on the extent of heart beat reduction, the degree to which
the blood supply is cut off to the limbs, the depth of their
dives, and the duration.

>>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

Olympic swimmers either cover their heads with a bathing
cap or cut off their head hair to reduce drag. Male swimmers
even find further advantage in shaving off their residual
body hair. In the latter case, I saw claims that shaving
off leg and chest hair cut times by 0.5 to 1 sec over 100m.
If they were as shaggy as the average chimpanzee I have
no doubt they would have registered an even greater
improvement by shaving.

>>2. Downward pointing nostrils (that stops water from being forced into
>>nasal cavities)
>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.

(a) Then why don't chimps and gorillas have something

(b) Who knows? Flesh and cartilage don't fossilize. The
nose is a bit short of musculature so one can't tell
the structure from muscle attachment points. Who knows
anything of the shape and dimensions of other fleshy
appendages in our early ancestors?

>>3. Descended larynx
>The neandertal larynx is only partially descended compared to our own.
>More importantly, newborn infants do not have a descended larynx.
Newborn infants have a priority need to be able to suckle
and breath at the same time. The non-descended larynx they
share with most other mammals lets them do both.

If the Neanderthal larynx is only partially descended, (and
this would be difficult to determine from bones alone)
that may indicate that further descent of the larynx was
required to facilitate fully developed speech.

>>4. Bipedalism (keeps legs, spine and head in one plane)
>There are no aquatic bipeds.

Penguins are aquatic bipeds. As you have frequently pointed
out, primates are partially adapted to bipedalism. Few other
mammal groups have such a predisposition and none of those
that made the transition from land to sea had it. If a
stranded population of apes made a partial transition to
an aquatic existence (the central thesis of the AAT), then
it would be the first example of a mammal so predisposed
to do so. The fact remains that all aquatic mammals maintain
their limbs, spines and skulls in a plane. Only one ape
does the same.

Pat Dooley