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Re: Tools and Brain Expansion
Mr J.M. Ottevanger (J.Ottevanger@LIVERPOOL.AC.UK)
Mon, 27 Feb 1995 18:36:15 +0000
Bob Graber writes:
>
> J.Langdon writes,
>
> >In tool, social, and foraging models we face the problem of why other species d
> >not have big brains. After all, chimps make and use tools, have complex
> >societies, and face similar foraging problems. Perhaps there is a threshold
> >effect -- once brains reach a certain size, positive feedback takes over and
> >increase proceeds exponentially. tion for
> >
> Note, though, that tool use and tool making is extremely rudimentary,
> which, in conjunction with the small brains of chimps, gives technology
> precisely the presumptive temporal priority required for it to have been
> causal. Therefore I think of a threshold not of brain size, but of tool
> dependency: at some point our ancestors became dependent enough on tool
> use that bipedalism and canine reduction--and brain expansion and
> symbolization--all were subject to growing selective pressure. I think
> it of utmost importance that only the Darwinian theory, which puts tools
> in the role of prime mover, allows explanation of all these hominid
> trends at once. From my perspective, any attempt to explain some one
> of the features suffers a considerable handicap in terms of parsimony.
> To compete with Darwin, you need to have a very strong argument that
> he was mistaken, or come up with a more compelling explanation of
> hominid features in general--especially the bipedalism/canine reduction
> combination, but preferably also language and brain expansion. It is
> amazing that the rather short-lived rotary-mastication hypothesis, about
> which I too am in search of references (a major one being Jungers in
> *Current Anthropology* of 1978), which is far less relevant than tools
> to *any* of the other hominid features, seems to be the most serious
> challenge to Darwin's theory in the 124 years since it was presented.
> But then he was Darwin, wasn't he? --Bob Graber
>
But why is tool manufacture the only route to parsimony? An overriding
environmental factor might also account for the appearance of the suite of
features you discuss, for example the climatic changes posited by Calvin
and others that have been mentioned previously in this thread. I don't
necessarily think that could tell the whole story for everything eg. bipedalism
(the recent evidence pointing towards this before a move to the savannah), but
a drier habitat may have favoured a striding rather than arboreally-adapted
gait, better (or different) food procurement and processing techniques, new
social structures, in short the flexibility that John Langdon describes. As
regards Darwin, yes, he had a lot to contribute to the matter but I don't
accept things simply because he said them. As regards the evolution of human
intelligence he was famously wrong - we did not develop big brains and
subsequently stand more and more upright, so I don't believe that the model you
cite is quite what he meant anyway. You admit that the canine argument is a
weakness (see social model for assistance), and I'd be inclined IF I INSISTED
ON ONE ULTIMATE CAUSE to plump for climate shift (see also Vrba) as the
overriding motor for the other suites of changes.
I'd really like to hear people's ideas about precisely what evidence we
most need to resolve the questions of cause and effect and the sequence of
events. Can they really be answered only by tenuous models? Or can we expect to
get much more from the fossil and archaeological record (Robert Johnson
permitting such an invasion of fossil privacy)?
thine, Jeremy
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