Marilyn Harris:
> Trying to figure out what they at would be guesswork though?

Scientists figure it out as best they can by studying the paleontological
evidence--mostly bones, teeth and coprolites (fossilized feces) from Stone
Age (Paleolithic) hunter-gatherers--and from studies of 20th century and
contemporary hunter-gatherers. (See Paleolithic Nutrition: Your Future Is In
Your Dietary Past, By Jack Challem, The Nutrition Reporter™,
http://www.thenutritionreporter.com/stone_age_diet.html.)

Marilyn:
> Does meat-eating increase life-span or brain-size?

Philip
> There is a hypothesis that it contributed to the evolution of larger 
> hominid brains, but it is hotly debated.

Marilyn:
> My impression is that meat eating increases size: look at the
> grizzlies of the northwest that eat salmon. They are the 
> largest bears on the continent sometimes even exceeding the 
> weights of polar bears. 

Your original question was re: brain size. Is the brain/body ratio of these
salmon-eating grizzlies larger than that of other species of bear?
Meat-eating primates do tend to have larger brains for their body size than
plant eaters, but apparently not always. Fruit eaters also tend to have
larger brains than leaf-eaters, so caloric density may be as important as
meat eating. But I don't have an opinion on the matter. I haven't drawn a
conclusion because the evidence is not clear.

> "Leakey thinks that the cooperation that hunting and
> sharing of meat required and encouraged was more important in the
> development of humans than the    "

...development of aggression, dominance and warring that hunting might have
enabled and encouraged (as portrayed in the movie 2001: A Space Odyssey).

I wasn't sure about the competing view that Leakey was arguing against and I
was tired, so my brain sort of shut down there and I forgot to finish the
thought (brain fart :-) ). Sorry about that. 

What Leakey was talking about is not actually brain size development, but
development of human social and behavioral characteristics and sophisticated
intellect. This might have fostered natural selection for larger brains or
might have been enabled by selection of larger brains, but he doesn't make
that argument directly. So Leakey is in essence saying that increased meat
eating led to the development of the human race because the coopertion that
hunting requires fostered the development of human characteristics. Here is
the hypothesis that Leakey describes (he did not develop it, he just did a
good job of explaining it):

<< ...people such as the Bihor in India and the Mbuti in the Congo basin
often hunt animals by driving them into long nets which are usually strung
in a long line through the trees; this type of hunting is impossible unless
individuals work closely together. And a currently popular view of human
evolution points to such co-operation between large groups of hunters as a
key element in the emergence of human characteristics.>> --Leakey, People of
the Lake

<<[Leakey] argues that at some point our hominid line developed a complex
economic system of gathering and hunting that required cooperation between
individuals in a clan. This cooperative system, besides being intrinsically
more productive, engendered the evolution of a special intellectual
capability on the part of our pre-historic ancestors. The brains of our
ancestors became increasingly subtle and complex because cooperation in a
society requires that its members be able to interact with each other,
empathize with fellow clan members, and take on specialized roles.

Leakey argues that this greater degree of "intelligence," along with the
inherent efficiency of cooperative societies, may have allowed the hominid
line to survive while our last cousins perished. Leakey develops this
argument carefully and logically so that when he holds it up to the
competing theory that our ancestors survived because they were more
aggressive and domineering, his view makes more sense.>> --J. Wyatt
Emmerich, "Leakey's Ancient Visions: People of the Lake by Richard E. Leakey
and Roger Lewin," http://www.thecrimson.harvard.edu//article.aspx?ref=142801