Re: Bipedalism and theorizing... was Re: Morgan and creationists
John Waters (jdwaters@dircon.co.uk)
20 Sep 1996 02:01:53 GMT
Paul,
As promised, Part Two.
[This is the second part of my reply to your letter of
16/09/96.]
As Apes are essential arboreal creatures they all have the
ability to brachiate (i.e. swing from branch to branch using
their arms.) Probably the best exponent of this is the Gibbon.
This Ape can also walk and run bipedally. It does this when it
needs to move along a tree branch. It doesnt walk quadrupedally
like a monkey.
On the ground, the Gibbon cannot use its main method of
transportation for obvious reasons. So it switches to its second
form of locomotion, namely bipedalism. It is very vulnerable to
predation on the ground, so it either walks very quickly, or
runs, from tree base to tree base.
The Gorilla and Chimpanzee can both brachiate in the trees. On
the ground, their main method of locomotion is knuckle walking.
Their secondary method of locomotion is bipedalism. This is
generally only used in aggressive displays by the males. In such
cases, the aggressive male may stand, stomp, pace around, or run
to produce a charging display.
If they cannot knuckle walk for any reason, they tend to switch
to bipedalism. An example of this was quoted by Jane Goodall in
her book, The Chimpanzees of Gorme. In this instance, a male
chimpanzee was affected by poliomyelitis. As a result, the
Chimpanzee lost the use of his right arm. As the male normally
moved on the ground by means of knuckle walking, it would be
reasonable to assume that it would modify its approach by
knuckle walking one handed. However, this did not happen.
Instead, the Chimpanzee switched to bipedalism, and learned to
walk considerable distances using this method.
(Ref. Goodall., J. The Chimpanzees of Gorme. The Belknap Press
of Harvard University Press. 1986. p. 93)
So to get back to our example Paul, I think the mother of the
still dependent infant would switch to bipedalism rather than
one handed knuckle walking. It is the secondary form of
locomotion for the African Apes, and most animals are pretty
conservative when it comes to changing their methods of
locomotion.
>From the point of view of predator avoidance, bipedalism would
have clear advantages because of the increased elevation of the
head and eyes. Furthermore, whereas with knuckle walking the Ape
tends to look at the ground, with bipedalism the head can
naturally scan the horizon for previously undetected predators.
In addition, a bipedal sprint would take the mother out of the
danger areas more
quickly that a single handed knuckle-walking, crawl.
Either way, the nursing females with the dependent infants would
only have to make it to the nearest point of cover, or feeding
place. Thereafter, within eight hours the infant would be no
longer helpless, and the female could knucklewalk as usual.
If the scenario of the bipedal sprint has any validity, then it
would be normal for genetic evolution of improved bipedal
characteristics to follow as a result of this behaviour.
Please note that the bipedal sprint would have no
thermoregulation consequences for the baby. The period of
contact with the mother would be too short for this. Infantile
thermoregulation problems would only arise when the female was
forced (by maternal instinct) to carry her baby for considerable
distances.
John Waters
John Waters is the author of "Helpless as a Baby",
a book concerned with general and human
evolution. It may be accessed at URL
http://www.dircon.co.uk/jdwaters/HAAB.htm
jdwaters@dircon.co.uk
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