On Fri, 7 Jan 2005 09:32, Rundle wrote:

>From: Keith Thomas
><< Why no parsnips or yams?  What about the 'Wrangham hypothesis'?>>
>
>Keith,
>
What is the 'Wrangham hypothesis'?

Dedy

Here's an extract from an interview about Richard Wrangham's hypothesis.  In a nutshell,
Wrangham suggests that the drivers for the evolution of the Homo species from
Australopithicenes was (a) the introduction of cooking and (b) that cooking made available far
more food in the way of 'underground storage organs': roots, tubers, corms and yams.
--------------------------
Richard Wrangham: Recently we’ve developed a new theory at Harvard which involves the fact that
where you see Australopithacenes evolving into early Homo around 1.9million years ago, you see
a series of changes that show a very strong signal of improved nutrition. Now that signal has
traditionally been argued as indicating that there was a great increase in the amount of meat
eating. Well, we looked at the amount of meat that is eaten and by ordinary estimates it is very
difficult to imagine that so much meat is being eaten that the quality of the diet seriously
improved to the point where you can get these bigger bodies with smaller teeth that indicate that
the food is essentially digested before it comes into the body.

The alternative that we’ve suggested is that cooking happens much earlier than people used to
think, and if you have food being cooked as early as 1.9million years ago it explains very easily all
of these nutritional changes. So then you say, well can it explain also an additional point that
nobody has previously satisfactorily explained which is that males, instead of becoming even
bigger as the females become bigger, become slightly smaller in relation to the females. In fact
the Australopithacene males are something like 50%, maybe 60% bigger than the females, and
now with the arrival of Homo erectus at 1.9million years ago we find instead that the males are
only 15% to 20% bigger than the females and that pattern is maintained absolutely, without a
change, right up to the modern day. So we see the whole gamut of human characteristics
happening at one point 1.9million years ago; at that point you get the nutritional signals
changing, you get the mating system changing and we think it all happened because of a good hot
meal.

Robyn Williams: Professor Richard Wrangham at Harvard two years ago. So how’s the theory
going? Here’s his colleague, also at anthropology, Jamie Jones.

Jamie Jones: About 2 million years ago we see this continuity in the fossil record where up until
that point all hominoids had been fairly small bodied, and from our best estimations they were
extremely sexually dimorphic, meaning that males were substantially larger than females. About 2
million years ago, with the advent of what we call Homo erectus, we see that females get
considerably bigger but males stay more or less the same, they get a little bigger too and as a
result sexual dimorphism is reduced substantially.

This is the first time we see a really dramatic shift like that in the fossil record. So we were
interested in explaining that and we found that the big difference that fire, cooking can play in
food preparation happens with underground storage organs; starchy, often tubers, they don’t
need to be tubers they can be corms, you know, grass roots and that sort of thing. And effectively
by cooking a tuber or an underground storage organ you double the energy availability because
the energy is stored in the form of these very dense starches and you break these up by cooking
them and they become available for digestion. So we hypothesised that the it’s the advent of fire
at this point that accounts for this difference in sexual dimorphism in this first really drastic
change that we see in the fossil record.
---------------------------
The full interview is at:
http://www.abc.net.au/rn/science/ss/stories/s262879.htm
but there are plenty of other sources on the internet.

Keith