"the development of genes that offset high cholesterol and chronic diseases
associated with a meat-rich diet, according to a new USC study."

('2.5 million years' later....)

'Atherosclerosis in the Masai.
Am J Epidemiol 95: 26–37, 1972.–
The hearts and aortae of 50 Masai men were collected at autopsy. These
pastoral people are exceptionally active and fit and they consume diets
of milk and meat. The intake of animal fat exceeds that of American men.
Measurements of the aorta showed extensive atherosclerosis with lipid
infiltration and fibrous changes but very few complicated lesions. The
coronary arteries showed intimal thickening by atherosclerosis which
equaled that of old U.S. men. The Masai vessels enlarge with age to
more than compensate for this disease. It is speculated that the Masai
are protected from their atherosclerosis by physical fitness which causes
their coronary vessels to be capacious.
http://aje.oxfordjournals.org/cgi/co...stract/95/1/26

"At some point – probably about 2 1/2 million years ago – meat eating
became important to humans,"

"This shift to a diet rich in meat and fat occurred at a time when the
population was dominated by hunters and gatherers,"

"For example, our ancestors only ate bird eggs in the spring when they
were available," he said. "Now we eat them year-round. They may have
hunted one deer a season and eaten it over several months. ."

And that's what they mean by a "shift to a diet rich in meat and fat"?

'The New Scientist September 16, 2007
Starchy tubers gave our ancestors' brains a boost
By Bob Holmes

A DRAMATIC shift in diet sometime during the evolution of modern
humans has left its imprint on our genome. The discovery could provide
some of the strongest evidence to date in support of a controversial
hypothesis that purports to explain why humans, alone among all the
apes, suddenly evolved such big brains.

One plausible reason is that early hominins suddenly stumbled on a new,
rich food source capable of fuelling a large, energetically expensive brain.
For many years, anthropologists presumed the crucial food source was
meat, which became more accessible as our ancestors began to use stone
tools for hunting or cutting. More recently, however, others have proposed
an alternative - starchy tubers. Proponents of this view argue that early
hominins had teeth better suited to grinding plant matter than tearing flesh.
Recent studies of isotope ratios in hominin fossils also suggest a plant-rich
diet.

But definitive proof is hard to come by. "We're talking millions of years
ago, we're talking perishable food items. We're just not going to find
archaeological evidence for it," says Nathaniel Dominy, an evolutionary
anthropologist at the University of California, Santa Cruz.

So Dominy and his colleagues decided to look for evidence in an unusual
place: our genome. They focused on a gene called AMY1, which codes
for salivary amylase, a starch-digesting enzyme. They already knew that the
number of copies of AMY1 varies widely from person to person, and
when the researchers surveyed 50 American college students of European
descent, they found anywhere from 2 to 15 copies. Moreover, individuals
with more copies had higher levels of amylase in their saliva. By contrast,
chimpanzees, whose natural diet contains very little starch, have just two
copies and very little salivary amylase.

The researchers then compared the genes of ethnic groups that traditionally
eat a high-starch diet - such as Europeans, Japanese and the African Hadza
people - with those whose traditional diet is very low in starch, such as the
African Datog and Asian Yakut. Those from a high-starch background
averaged 6.72 gene copies, significantly higher than the 5.44 copies carried
by those from a low-starch background (Nature Genetics, DOI:10.1038/ng2123).
"We think that selection is strongly favouring more copies in populations
with more starch in the diet," says Dominy. The study is one of the first to
show that natural selection can lead to an increase in gene copy numbers.

If that increase coincided with the dramatic expansion in our ancestor's brain
size about 1.8 million years ago, that would be the strongest possible evidence
that roots and tubers, not meat, fuelled our intelligence.

http://www.newscientist.com/article/...s-a-boost.html