On Fri, 4 May 2001 08:10:50 -0500, Philip Thrift <[log in to unmask]>
wrote:


>>Could you point out which time and which food you mean?
>
>See erectus-sapien brain comparison at
>
>   http://www.handprint.com/LS/ANC/brain.html

Nice site, nice graphics.
You can see, that between the brain of homo erectus and our brain there's
a different size and shape. That's not new.
But it explains that you mean the last step between erectines and us
as deciding (note that the biggest brain expansion in volume was
before, towards the erectines).

However what misses is the kind of food you attribute to each kind
of hominid, particularly where the >50% animal calories were present.
The map at http://www.handprint.com/LS/ANC/disp.html (bottom)
shows very good where these hominids lived, and what kind of vegetation
(and therefore fauna too) was found there.
You can see that at the places where the earlier artefacts were found
(heidelbergensis and erectines) there was always some woodland, between rain
forest and open/mountain woodland.
I can't see any artefact sites prior to neanderthal which is
on a tundra area. Where Ray locates his megafauna.
No walrus there. Nice lean Zebras. (;-)

Note that the map is for 18,000ya, at a glaciation maximum.
In the thermals (alternating with glaciation every few 10k years) the
woodlands would even expand very much.

The time frame
>   http://www.handprint.com/LS/ANC/evol.html#chart
nicely shows that between the species h.heidelbergensis, neanderthal,
erectines there are unclear connections.
Erectines lived in parallel to neanderthals and to heidelbergensis.
The developement happened in some jumps and suddenly somewhere between
the end of heidelbergensis or erectines but long after neanderthals were
a stable population
- and voila - the modern human appeared.

I note that the times of brain enlargement were different from the time
of megafauna hunting.

I note too that the big hunter population of the north, the neanderthals,
had bigger brains as we have. There must have been some need for.
Maybe more chances to recover after a strike on the head from a bear.
Or a better resistance of more brain cells against the waste from ketosis
(a feature we seem to share).

>Also see
>
>   http://www.beyondveg.com/billings-t/comp-anat/comp-anat-4b.shtml

Beyondveg here presents the expensive tissue hypothesis. Basically:
Increased energy demands from the brain demand a food higher in energy.

They forgot in the course of beyonding against vegetarianism, that
meat is a lousy energy source, particularly  for the brain.
Brain prefers glucose. I still wait for the explanation.
Expensive tissues (brain) demand high carbohydrate, high energy food
(as tubers and most seeds would be).

At last, the DHA explanation theory for the recent reduction of brain size
of 8% (in the last 10k years). I can't suscribe to this point of view.
If DHA (synthesis) is enough to build up the human brain in each baby
since millenia, why should it shrink only 8 percent without dietary DHA?
The human brain is *300* percent bigger than that of it's predecessors.

I take less concussions (which kill many brain cells) as a possible
explanation for the a smaller skull size.

Your first link (above) points out that the enlarged front lobe and
"pariental" lobe makes up a main difference between modern humans and its
predecessors, "including Neandertals".
Was it the increased front lobe what made the big leap possible?

Regards,
Amadeus