Re: Bipedalism and theorizing... was Re: Morgan and creationists
Paul Crowley (Paul@crowleyp.demon.co.uk)
Sat, 21 Sep 96 11:59:30 GMT
In article <01bba692$79401720$1d2470c2@jdwaters.dircon.co.uk>
jdwaters@dircon.co.uk "John Waters" writes:
> 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 is an example of the "evolution forces" argument. It is a
common one, but it is still bad. What happened to all populations
of virtually all species living in the Sahara when the recent
dessication took place? Did they adapt to a drier climate? No,
of course not. They just died. That is the predominant effect of
climatic change. Adaptation, if it is going to occur at all, is
much more likely to happen in good times rather than in bad ones
-- when a small population of a dynamic species finds a new niche.
> 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.
I would not accept this at all. An extension of infantile
helplessness is so disadvantageous that almost any way around it
would be found. I can see no reason why brain (or other skull)
development could not be postponed till after birth. All the
infant needs is the ability to hold on; that simple reflex
action is possessed by numerous species with small brains.
> 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.
This is the central point of your case. IMO it's very weak.
For example, male and female infant gorillas are identical in
power/weight ratios and in skull and body size. Yet they grow
up to be very different in these respects. Even if we allow that
there was a compelling adult need for a better power/weight ratio
(and I don't) there is no necessary effect on infant altriciality.
> Of course, if the climatic conditions are very severe, the rate
> of evolution can be much faster.
I'm afraid this is nonsense. They just die faster. That's all.
> 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.
Consider the advantages of the closely related mother with an
infant that could hold on in the normal primate ventral
position. She can "gallop" quadrupedally. She can dash through
relatively dense bush. She can scoot up a tree. Mothers with
helpless infants would get wiped out and be replaced by their
more effective quadrupedal cousins.
Paul.
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