Re: Bipedalism and theorizing... was Re: Morgan and creationists
John Waters (jdwaters@dircon.co.uk)
20 Sep 1996 01:28:57 GMT
Paul Crowley <Paul@crowleyp.demon.co.uk> wrote in article
<842908430snz@crowleyp.demon.co.uk>...
> > . . . . There would be no
> > question of .... mothers with slowly developing infants
> > competing directly with .... females who had faster
> > developers.
>
> Why not? You are trying to duck the issue. >
> Paul.
>
JW: As incisive as ever, and (quite rightly) going straight for
the jugular. Permit me to dodge the central question a little
longer while I answer some of your other questions.
The advantage of this development was an improved power to
weight ratio. Forget about larger brains. They may be the
standard answer, but they are not my answer. No, I repeat. My
answer here is improved power to weight ratio. (Note: there is
an alternative answer. See my reply to Phillip Bigelow. Post.)
The developments we are talking about here took place about 4.5
to 7 Mya, in the Pliocene epoch. This was a time of great
climatic change, when the terrestrial environments became much
drier. The ancestor Apes food sources became much more
scattered. The distances between food sources became longer and
longer.
The hominids' Ape ancestor adapted to the changes by improving
its power to weight ratio. This gave it greater endurance, and
the ability to traverse longer distances on a reduced quantity
of food.
The potential disadvantage of this development was the increase
in the period of infantile helplessness after birth. However,
the potential disadvantage did not translate into an actual
disadvantage in the early stages of this development. The reason
for this is that the nursing female (typically) stays in the
birthing place, ( the place where she gives birth to her baby),
for three days.
Let me illustrate the position. Let us say (for sake of
argument) that the normal mothers have babies which are helpless
for 24 hours after birth. By contrast, the mothers who have
inherited an improved power to weight ratio have babies which
are helpless for 28 hours. However, by the time both types of
mothers have to move out of the birthing place (72 hours), both
types of babies can hang on to their mothers in the usual way.
The more slowly developing infants then grow to adulthood in the
normal way. However, because they have a better power to weight
ratio, they are more likely to survive in times of drought etc.,
when there is a premium on extra endurance. If these later
developers form 2 percent of the species population, then after
such a drought their relative proportion could increase to (say)
4 percent. If there was a severe drought in every generation,
then after fifty generations the later developers would be the
species norm. As such, all babies would be helpless for 28
hours after birth. This is what I meant by the term slow rate
of evolution, in my last letter.
I am sorry to labour this point, but some readers may be unaware
that evolution often takes place by means of a series of tiny
steps, which means that the process takes a long time (relative
to the life span of the individual). Of course, if the climatic
conditions are very severe, the rate of evolution can be much
faster.
Returning to our example, the new 28 hours norm of infantile
helplessness would continue to be extended gradually. 28 hours
would be replaced by 36 hours, and so on until the norm of
infantile helplessness was 72 hours. For the sake of argument,
let us say that the mothers with a further improvement in their
power to weight ratio
had babies which were helpless until 80 hours after birth.
This brings us to the central question which I think you are
asking. Namely: what happens when the disadvantage of an
extended period of infantile helplessness becomes apparent. In
this context there is no disadvantage as long as the mothers are
able to stay in their birthing place. But what happens when the
period of infantile
helplessness is so long that the mother has to move out of the
birthing place with a still helpless infant?
In this case, the normal mother who has an infant whose period
of helplessness lasts for 72 hours can move out of the birthing
place in the normal manner. Her infant is no longer helpless,
and can hang underneath its mother in the usual way. So the
mother could be expected to knuckle walk to the new feeding
site, or next bit of
protective cover.
The motive for moving is to get food, while avoiding predators.
In a semi-equatorial savannah environment, there tend to be
clumps of bushes or trees, interspersed with open grassland or
low scrub. The nursing females would need to traverse the open
areas as quickly as possible to avoid the attention of
predators.
The mother of the still helpless infant could not move out in
the usual way. She would have two alternatives. Either she could
travel by means of single handed knuckle walking, holding her
baby in her other hand/arm. Or she could walk (or run)
bipedally, holding her baby in one arm or both arms.
Before trying to decide which of these alternative methods of
transportation would be adopted, I think we should consider the
facts relating to Ape locomotion.
[This looks like being another long reply Paul, so to avoid the
ire of
SAPs Controller, I propose to continue this in a second reply
which I
will title Part Two to avoid confusion.]
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