Re: Bipedalism and theorizing... was Re: Morgan and creationists
John Waters (jdwaters@dircon.co.uk)
28 Sep 1996 20:42:34 GMT
Part 3.
And so back to hominid evolution.
At this stage I think we should listen to the words of wisdom
recently uttered by your good friend Phillip Bigelow. (See
article 26/09/96).
>>The *point* in such quotes is that this newsgroup is a science
>>newsgroup, and the results from basic research and direct
>>scientifically-conducted observation should take precedence
>>over idle speculation for the sake of speculation.
JW: The point is this, Paul. We have both been speculating upon
the probabilities and possibilities concerning a switch from
knuckle walking to bipedalism. However, all available evidence
shows that hominids never used knuckle walking. Their fossils
never show the strengthened digits which are typical of knuckle
walkers.
This raises the question of how they moved on the ground. If
they did not knuckle walk, what did they do? Did they turn
somersaults? Do backflips? Cartwheels?
If the Gibbon analogy has any value, then it is most probable
that they were bipedal on the ground. Not good bipedalists
perhaps, but bipedalists nevertheless.
According to all the evidence, the Gorilla/Bonobo/Chimpanzee and
their ancestors only evolved knuckle walking after their
collective split from the hominids. This raises the question of
why did they evolve knuckle walking. Why did they not become
bipedal?
My answer to this question is that they became knuckle walkers
when they needed to traverse relatively long distances on the
ground. And their physiology, coupled with the fact that their
infants could hang on to their mothers, encouraged the
development of knuckle walking.
Of course, my speculation may be wrong here. But it shows the
value of basing speculation on factual evidence. For if knuckle
walking was the appropriate response for the African Apes at
this point in their evolution, why did the hominids not follow
suit when they reached a similar point in their evolution?
It is here that the Helpless Baby Theory starts to stand head
and shoulders above the rest. This theory has a very credible
answer, namely the helpless baby. It had to be carried with one
arm or both arms. So the hominids stayed with bipedalism.
I know you are still sceptical about this power to weight ratio
business. However, it makes a lot of sense in the context of a
marginal variant evolutionary change.
In my view, the hominid development was the result of such a
change. There was a mainstream ancestral African Ape which was
the common ancestor of the hominids and Gorilla/Chimps. The
mainstream ancestral Ape environment was sufficiently gradualist
to allow an inhabitable marginal environment. Individuals with
non-standard characteristics were forced out of the ancestral
Ape's mainstream environment. When they reached the periphery,
most of them died. However, some of them had characteristics
which were suitable for a marginal environment. These survived
and mated. This process led to a marginal variant specie.
It should be noted that in any Ape population there are big apes
and small apes. In addition, some Apes will have better long
term memories than others. As long term memory is dependent upon
brain capacity, these apes would have larger brains than those
who only had short term memories. In a social specie, the lack
of good long term memory is not a great disadvantage, because
the group can benefit from those individuals who have a good
memory.
I am bringing up the subject of long term memory here, because
it is more important to survival in a marginal environment.
Remembering the whereabouts of food sites is a tremendous asset.
In Ape specie, at times of scarce food resources, the dominant
Apes tend to drive the subordinate Apes out of their
territories. So the ancestral group in the marginal variant
specie would tend to be made up of small bodied subordinate
individuals and large bodied (and brained) subordinate
individuals. Their progeny could exhibit three different
combinations of physical characteristics. Namely:
1. An individual with a big body and a small head. This would be
the worst configuration.
2. An individual with an average body and an average head. This
would be the second best configuration.
3. An individual with a small body and a large head (and large
brain). This would be the best configuration.
Notice that the large brain is no larger than that of the
mainstream Ape. However, this last configuration couples good
long term memory with a body which has a relatively good power
to weight ratio.
The importance of long term memory in the context of a marginal
environment is fairly obvious. The best available power to
weight ratio is important because the individuals have to climb
as many trees as before, but get the lower quantity of food
which is typical of a marginal environment. Hence they need
light bodies and good
endurance characteristics.
The disadvantage of large head/small body configuration, (or
mosaic of characteristics), is the extension of the period of
helplessness of the baby. So it all comes down to a question of
relative advantage. I think I have already made my case on that
question.
John.
Paul Crowley <Paul@crowleyp.demon.co.uk> wrote in article
<843593383snz@crowleyp.demon.co.uk>...
> In article <01bba9fd$483b81a0$152470c2@jdwaters.dircon.co.uk>
> jdwaters@dircon.co.uk "John Waters" writes:
>
> > 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.
> > [snips]
> >
> > The marginal variant specie are typically generalistic
> > omnivores. The specialist mainstream specie tend to be
> > frugivores, or carnivores, or leaf eaters, or graziers.
>
> We're really talking about all species - fauna and flora. Are
> such rules well recognised? I've never heard of them.
Clearly
> if whole species are wiped out by drastic climatic change
(such as
> that at the K/T boundary) then new niches open up, enabling
rapid
> radiative adaptation. But does it apply to normal climate
change?
>
> > .... Secondly, you need an empty niche
> > which can be colonised by the new variant specie.
>
> This is the vital feature, which is missing from normal
scenarios.
>
> > 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.
>
> How can you say this? Of terrestrial animals H.s.s. must be
one
> of the most water-dependent. We sweat intensively. Our
faeces
> are 75% water. Our water-retention mechanisms are minimal to
non-
> existent.
>
> > > 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.
>
> We agree that additional helplessness for a primate infant
(and
> its mother) is disadvantageous. You say, however, it leads to
a
> better power/weight ratio. Your logic here is extremely
unclear.
>
> In any case, I'm sure that "a better power/weight ratio" is a
> chimera. How could, say, chimps or dogs or dolphins achieve
a
> better power/weight ratio? They are each as well adapted to
their
> current environment as is possible. They are each the result
of
> millions of years of evolutionary weeding-out. Insofar as the
> real world allows, they have an optimum power/weight ratio.
>
> Perhaps you are saying that certain populations adapted to a
> different environment. If that's the case, say so. The
power/
> weight thing seems to me a distraction.
>
> Paul.
>
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