Prehistoric humans and meat query (long)

Anita Cohen-Williams (IACAGC@ASUVM.INRE.ASU.EDU)
Tue, 31 Jan 1995 12:44:28 -0700

(Chico, California) on Wednesday, January 18, 1995.


Carnivores, take heart. Meat-eating is what made humans brainy.

Scientists say the move away from an all-vegetarian diet triggered the
growth of human intellect. In other words, our love of a nice chop has made us

Until early humans began eating protein and carbohydrate-rich meat, their
metabolic resources were absorbed by energy-demanding digestive systems that
had to process vast amounts of vegetation, according to a forthcoming paper in
the journal Current Anthropology.

But about 1.8 million years ago, our predecessors, homo erectus, changed
behavior. They stopped being vegetation-only foragers. Around this time,
primitive scrapers start appearing in the fossil record [sic], near the bones
of pigs, hippos, buffalos and other animals. Either humans were killing them,
or they were scavenging in the wake of other carnivores.

"It was not just meat but fat and bone marrow that were being consumed,"
adds Dr. Leslie Aiello, of University College London's anthropology
department. "And such easy-to-digest foods require smaller stomachs and
intestines, which use up less energy. That surplus fed our brains, which began
to grow significantly.

"It was a loop. We started to eat meat, got smarter and thought of cleverer
ways to get more meat."

However, Aiello said meat wasn't the only nutritional trigger. Once we
started to get smarter, we were able to obtain other rich, but easily
digestible, forms of nutrition, such as nuts.

The paper by Aiello and her colleague, Dr. Peter Wheeler, of John Moores
University, Liverpool, points out the human gut is the only energy-demanding
organ that is markedly small in relation to body size compared with other
mammals' - about half what one would expect.

"And small guts are compatible only with high-quality, easy-to-digest food,"
they say.

On the other hand, the size of the human brain is strikingly large. It
should weigh about 10 ounces for a mammal of our body size. In fact, it weighs
almost 3 pounds.

And if you look at the fossil record, and at apes, you see anatomies that
support this point: both display pyramid-shaped rib cages that get larger as
you move further down the body - to make way for massive stomachs and coils of

Homo erectus, and modern humans, have barrel-shaped rib cages which open out
to make way for the lungs, and then contract over the small gut areas.

Of course, meat-eating doesn't make all carnivores clever. It was just that
in the case of early mankind it permitted an already smart creature to get
even smarter.

Until then, our brain size was curtailed because, as Aiello puts it, "as a
species, you cannot have a big brian and big guts. Providing energy for both
would have kept you so busy you would not have time for reproductive

But why did early humans pick this moment to begin meat-eating?

"There was a great deal of environmental change going on around two million
years ago in East Africa," Aiello says. "And that brought a lot of
evolutionary pressure on all animals who had to adapt or perish."

At this time, vegetation was drying out. Some australopithecine apemen, the
predecessors of homo erectus, developed huge jaws and guts to process
unappetizing leaves and grasses. They became extinct, however.

Our ancestors adopted, by chance, a more flexible approach, developing
strategies for eating all sorts of different foods - including meat.
"That was our good luck," adds Aiello.

But that wasn't the end of the story. A second wave of human brain
increases began around 400,000 to 500,000 years ago, one that led eventually
to that "noonday brightness of human genius," as Bertrand Russell described
the intellect of homo sapiens. And this second leap in brain power came when
our predecessors began to use fire.

"Cooking is a technological way of externalizing part of the digestive
process," according to Aiello and Wheeler.

In other words, cooked food requires even less digesting and so reduced
further the size of our guts, permitting further increases in brain size.

Our growth in intellect, therefore, appears to have started with a good raw
steak and was completed with a plate of stew.

Certainly, we have a lot to thank our carnivore predecessors for. Thanks to
their meat-eating, we have become an intelligent species - clever enough even
to choose to be vegetarians.

Anita Cohen-Williams; Reference Services; Hayden Library
Arizona State University, Tempe, AZ 85287-1006
PHONE: (602) 965-4579 FAX: (602) 965-9169