Also we have subcutaneous fat like pigs, otters and other semi-aquatic
animals. Human babies can be born in water and naturally float; try this
with a baby chimpanzee and you end up with a dead chimp baby. Elaine Morgan
has championed this view originally put forward by Sir Alex Hardy in the
1960s in the book "The aquatic ape" (1982, Souvenir Press).
One of their strongest arguments is that we are have a diving reflex -- put
your body under water and your pulse rate automatically drops to conserve
energy -- and this is something that seems to be lacking in other apes, but
exists in aquatic mammals like the seal.
In addition to subcutaneous fat our nose and nasal passages are constructed
such that we can dive (and have showers!) without getting water in our
lungs. Again try this with a chimpanzee.
The idea is that our ancestors learnt to foraged in shallow waters for food
and bipedalism could by explained as an evolutionary pressure to help us
stand upright in shallow waters while we foraged.
There is even a suggestion as to when this might have happened ~6.5 million
years ago the Danakil Alps in the Afar triangle of Northern Africa became
islands and any in this area would have been cutoff from the African
mainland for over a million years. During this period they may well have
learnt to exploit food along the coast and become so suited to this aquatic
lifestyle that may of the features we now take for granted -- bipedalism,
lack of hair, subcutaneous fat etc had already developed -- when they
returned to the African mainland to continue their evolutionary
development.
And of course other arguments used for bipedalism (e.g. it developed as a
way to keep body temperature down on the hot savanah) are not incompatiable
with the idea that it originally developed to for a semi-aquatic lifestyle
and then was used by evolution for other reasons.
The problem with this theory is that it lacks any hard fossil evidence and
I doubt whether any palentologists take it seriously today. Of course its a
little hard to think what would be really knock-down evidence for or
against. And no one seems to have explained why we do have a diving
reflex...
If you want to find out more I suggest you check out:
http://huizen.dds.nl/~seismo/aat.html
best, patrick
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Patrick Wilken http://www.cs.monash.edu.au/~patrickw/
Editor: PSYCHE: An International Journal of Research on Consciousness
Secretary: The Association for the Scientific Study of Consciousness
http://psyche.cs.monash.edu.au/ http://www.phil.vt.edu/ASSC/