Re: An alternative to ST and AAT
Paul Crowley (Paul@crowleyp.demon.co.uk)
Sat, 16 Nov 96 19:41:56 GMT
In article <56huv7$mt6@news.NL.net>
G.Hanenburg@inter.nl.net "Gerrit Hanenburg" writes:
> Paul@crowleyp.demon.co.uk (Paul Crowley) wrote:
> >I'm sure that the proto-hominids would have achieved a high degree
> >of social co-operation. This implies terrestriality and not a
> >rain-forest habitat. So its use would have been new.
>
> The logic escapes me. Why does a high degree of social co-operation
> imply terrestriality? How do you know that proto-hominids had a high
> degree of social co-operation?
The logic is simple. A high degree of social co-operation implies
terrestriality because we observe that arboreal apes are not co-
operative; they do not need to be as they have no predators
(other than H.s.s.). Further they only occur in dense rainforest
where trees come into fruit on an erratic basis so foraging
techniques favour individuals or very small groups and they will
have neither occasion nor reason for developing sociability.
On the probable high degree of social co-operation in proto-
hominids: The "coalition of screaming males" you refer to later,
amoung early hominids is almost conventionally assumed; I hope
you don't want me to argue for it. If it was present in early
hominids it's parsimonious to assume it in proto-hominids.
Further since chimps possess it now, and since our DNA and some
fossil evidence strongly indicate a close association with them,
the most reasonable inference is that proto-hominids were quasi-
chimps, with both terrestriality and co-operation.
> Please can we have an answer that goes beyond mere speculation?
> You often say "I'm sure that...." while your certainty has no
> empirical ground whatsoever and as such has as much scientific value
> as a religious belief.
Why not try to make out an alternative case? We can only try
to draw conclusions from the evidence we have. I think we have
more than enough.
Susan's point: "Afarensis' sexual dimorphism suggests a high degree
of competition among the males for access to females" is IMO no
more than a weak suggestion drawn from a very general mammalian
rule. The dimorphism could have had many other origins.
> >Why did the bipedalism retain these strange climbing
> >adaptations? (If that is what they were.)
>
> Why strange? Is it strange that chimpanzees combine quadrupedalism
> with arboreal adaptations? Apparently,in your mind there is only one
> possible evolutionary path to bipedalism,and everything that deviates
> from it is considered strange.
"Strange" means "unexplained" or "inexplicable". And a "climbing
adaptation in some other arboreal context" does not constitute an
explanation. Science is about seeking explanations. There was
only one evolutionary path to bipedalism, not a multiplicity.
> Why do you persistently insist on this detail when there are no means
> to assess it? What does it help you if I conjecture that she spend 15%
> of her daily feeding time in the trees? How are you going to falsify
> that?
Any discipline that accepts vague generalities as answers is in a
bad way. I'm suggesting that as soon as you try to fill out your
hypothesis with any detail, you will see that it does not work.
So I would ask you how such a 15% time could have yielded enough
benefits to compensate Lucy for the costs of reduced bipedal
capacity, by comparison with a female H.erectus. I would ask you
to describe how each of them coped with their small infants and
other young during such activity. Increasing the period to 30%
or 45% makes it worse. I cannot see Lucy's morphology providing
any significant advantages at all in this context.
> Chimpanzees,after several million years still aren't very good
> quadrupeds. What keeps *them* from becoming so if efficient
> quadrupedalism is such an advantage?
We can see the reasons easily. Their four prehensile limbs
enable them to survive nocturnal predators, and when small they
can hold onto mother while she climbs high trees to forage and
they can escape predators by swinging out to smaller branches.
> >What could Lucy do that H.erectus couldn't?
>
> Let's try to answer the question with comparative material.
> What can a chimp do (better) that a modern human can't?
> Hmm..........climbing?
There is nothing wrong with the original question. Changing it
is not an answer. However: "climbing" is far too general an answer
to any such question; it's how they sleep at night (with infant
attached), how they forage (with infant attached), how they escape
predators . . . In each case it's chimps on one side and _all_
hominids on the other.
> Then please tell me in all detail what this edge is that Vervet
> monkeys are supposed to have over Savanna baboons.
Anyone who has detailed knowledge of these species (not me at the
moment) could tell you this. A major difference in size usually
makes it easy and Vervet monkeys are much smaller. They do not
move far from trees and, presumably, can forage higher. Vervets
can, presumably, occupy trees that would not be suitable as night
refuges for baboons, thus giving them a different range.
> How species A and B interact may depend on how species B
> and C interact,and this in its turn may depend on the interaction
> between A and C.
Explanations of "edges" of the Vervet/Baboon nature usually require
no more than a minimum of investigation. Delving into complexities
of interactions is rarely needed when outlining the niche of a
medium to large-size mammal.
> There are the hypotheses of the origin of bipedalism as a feeding
> adaptation. See for example Hunt,K.D.(1994),The evolution of human
> bipedality:ecology and functional morphology. Journal of Human
> Evolution 26:183-202.
>
> Then there are the ones that emphasize physiology. See for example
> Wheeler,P.E.(1984),The evolution of bipedality and the loss of
Thanks for the references. I'm familiar with most of them.
But, surely you agree that, in spite of their thoroughness and
apparent scholarship, they are all almost embarrassingly bad?
This can be seen by assuming one is right and asking where that
would leave the others. Why are they so bad? The answer has to
be that one or more of the basic, but unquestionable, assumptions
is wrong. I suggest that one is the "savannah hypothesis" or as
Phil Nichols would say: "the _fact_ that our ancestors lived on
the savannah".
Paul.
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