buoyancy & the position of the head
From: Marc Verhaegen (fa204466_at_skynet.be)
Date: 12/14/04
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Date: Tue, 14 Dec 2004 09:32:35 +0100
Algis at AAT + answer of Michael Burns:
> Has anyone noticed how the way humans float in water is very
> sensitive to the orientation of the head? Try it. Go into a pool,
> take a deep breath and just let yourself float.
>
> If your head is in the 'normal' position for a human walking (or it
> is bent forward) your body will rock forwards and the centre of your
> back will typically be the part of the body to surface. (I think
> this is true in females too, but I've only tried it on me, my wife
> and kids so far)
>
> Now, here's the fascinating bit: lift your head back as far as it
> goes and, rather amazingly, your body will re-orientate itself in
> the water with your nose and mouth rising slightly above the
> surface. This will depend on your buoyancy (and that is largely a
> function of how fat you are, I'm afraid) and also, of course, how
> much you have inhaled. But if you are either fat or have inhaled a
> lungul of air you should, in theory, be able to float and breath
> with absolutely no effort at all.
>
> The interesting thing is that Stephen Munro told me the other night
> (fantastic evening, Steve, thanks again!) that Homo erectus has less
> basio-cranial flexion than humans and so the orientation of the
> upper head and face was, to them, more naturally, upward looking
> than it is to us. Stephen made the point that this orientation would
> make more sense for swimming, and i think he's absolutely right.
> But, judging by this peculiar little observation, perhaps it would
> also help them to float effortlessly, rather like a hippo does, with
> its breathing holes out of the water, even if it were unconscious -
> assuming it had sufficiently greater bouyancy than us.
>
> Any thought or comments?
>
> What I want to know is this: How cxan such a minor change in head
> position alter the way the body floats in water? What do people
> think is going on?
>
> By the way, I met Stephen Munro in Canberra after giving two talks
> on the AAH at the ASHB conference and I won first prize for student
> presentations. Several eminent people told me that they thought that
> some seem to be changing their minds about this idea at last.
>
> My emphasis was that the AAH has been misunderstood. If we take it
> merely as the hypothesis that water has acted as an agency of
> selection in human evolution more than it has in the evolution of
> our ape cousins, I think many people would support it. In particular
> the wading hypothesis for bipedal origins seems to be rapidly
> loosing it's controversial image and is well on the way to becoming
> a mainstream hypothesis.
>
> I hope people will agree with me that this is a very encouraging
> develoment.
>
> Algis Kuliukas
Definitely! This is _very_ encouraging, I suppose the ASHB might be a
somewhat enlightened atmosphere since they have long had the He on Flores
staring them in the face, so to speak, and congratulations on winning first
prize.
Some people on the list think we were significantly more adapted for time or
activity in the water than we are now, but I think your conservative
formulation is very reasonable. If there is ever evidence of something more,
we can go from there. I myself don't see reason to suppose that we did more
than spend a large part of our food-gathering time in the water.
As for floating, I grew up in Lake Michigan (summers anyway), often spending
8 hours a day in the water in spite of the fact that the water is considered
a bit cold for Hs. I made money a couple times by proving that I could float
with my hands tied to my ankles behind my back. (I also did this in a pool
into which I was pushed and initially went to the bottom) . The key, as you
indicate, is to resist panic and keep your lungs completely full of air.
Apart from that I have also slept for a short time while floating by simply
training myself to a quick exhale-inhale/long-hold cycle.
I suspect we have several small abilities that need to be triggered by early
use. I was thrown into the lake at age 3 and told I could swim; sadly, I
have retained the help-I'm-drowning style for surface locomotion ever since.
Swimming underwater I do elegantly though :-)
Michael Burns
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