Re: Bipedalism and theorizing... was Re: Morgan and creationists
John Waters (jdwaters@dircon.co.uk)
24 Sep 1996 09:51:15 GMT
Paul Crowley <Paul@crowleyp.demon.co.uk> wrote in article
<843422675snz@crowleyp.demon.co.uk>...
> > JW: ^^^^^^ You appear to be talking about short term
> > behavioural adaption, which occurs within an individual's
> > lifetime.
>
> No. I am, of course, talking of long-term genetic adaptation.
> This error of yours is important to correct because it's basic
to
> your theory. It's also very common. Think of chimpanzees
just
> south of the Sahara - the boundary has been there for millions
of
> years, sometimes much further north, sometimes further south.
> The chimps on the boundary have been under constant pressure
to
> adapt to a drier habitat. They have not done so (for obvious
> reasons). Now let's say that from 2 mya to 1 mya there was a
> general trend towards dessication. IOW the boundary generally
> moved south in that period. How would that have changed
anything?
> You'd have about the same number of chimps in any generation
> exposed to the same pressures. IOW a period of climatic
change
> does *nothing* to "force" adaptation.
>
JW: Generally speaking genetic adaptions occur under one of two
sets of conditions. The first type of condition occurs when the
global climate changes from cool dry to warm wet. This is
significant because there are more potential ecological niches
in a warm wet environment. Under these conditions you get the
radiation of specie as they adapt to these new niches.
The second condition occurs when a mainstream niche has an
extensive marginal niche potential. In this case, individuals
who are not competitive in the main niche are forced into the
marginal niche. Most of these individuals die. However, the
survivors have a very varied set of non standard genetic
inheritances. When they mate, their progeny inherit the non
standard combinations and the optimum characteristics for
survival in the marginal niche are selected for. In time this
results in a new marginal variant specie. The variant specie
cannot compete with the mainstream specie in a mainstream
environment. Likewise, the mainstream specie cannot compete with
the variant specie in the marginal environment.
When the global climate becomes tougher -- typically cooler and
drier; the mainstream niches reduce, and the marginal niches
expand to take their place. Eventually, the mainstream niches
dissappear altogether -- taking the mainstream specie with them.
Only the marginal variant specie, which is preadapted to
marginal conditions, can survive. When the global climate
changes back to warm and wet, the marginal specie is the one
which radiates into the specialist mainstream specie.
The marginal variant specie are typically generalistic
omnivores. The specialist mainstream specie tend to be
frugivores, or carnivores, or leaf eaters, or graziers.
So the conditions for long term genetic adaption are that
firstly you need an adaptable specie -- the sort that can give
rise to a specie radiation. Secondly, you need an empty niche
which can be colonised by the new variant specie.
Clearly, the Chimpanzee is a generalistic omnivore. So the first
condition for adaptive change is satisfied. However, there is no
empty neighbouring niche. On the equatorial side, the Ape niches
are occupied by Gorillas and Bonobos. On the desert side the
niche is occupied by the human specie. As far as we can tell,
this has been the case for the past five million years. So it is
no surprise to find that the Chimpanzee has not adapted to
desert or equatorial conditions.
> >
> > JW: As explained in my letter, there would be no initial
> > disadvantage because the nursing female would stay in her
> > birthing place for the first three days after giving birth.
>
> You can break down *any* evolutionary development and say that
the
> change in each generation would be so insignificant that it
would
> have no disadvantageous effects. That's plain cheating. You
have
> to outline the countervailing advantages.
JW: I Have. An improvement in their power to weight ratio. I say
this again and again, and you ignore it again and again.
Perhaps you would like me to propose the alternate head to body
ratio scenario. The alternative adaptive change in generally
known as the seed eating model (* after C J Jolly). In this
case, the body stays the same size and the head gets bigger.
However, there is no increase in brain size. The reason for the
head getting bigger is that the specie adapts to eating tougher
foods -- and this leads to larger teeth, jaws, jaw muscles and
their related attachement points. The result is the same, namely
a change in the head to body ratio. There is plenty of evidence
of this sort of change in the Australopithicine fossil record;
and in some cases this was accompanied in due course by an
increase in brain size.
Which begs the question. If these sorts of adaptions could occur
a number of times in the Australopithicine and early Homo
periods then why could they not have occurred prior to the
Australopithicines?
>
> Chimp mothers with infants attached often use a two-beat
> "gallop", alternating between hind and forelimbs. It's fast.
JW: I accept this. And of course I accept that the normal mother
would have advantages in terms of infant transportation.
However, in the context of an intelligent and resourceful social
specie, I do not believe that the "crippled" hominid would be
seriously disadvantaged given the very short timescale involved
(eight hours). Nursing females tend to travel near the centre of
a group of social Apes, and predators rarely attack large groups
of apes.
John
* Ref: Jolly. C.J., The Seed Eaters : A New Model of Hominid
Differentiation Based upon a Baboon Analogy. Man. N.S. 5
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