By Gilien Silsby and Gia Scafidi When our human ancestors started eating
meat, evolution served up a healthy bonus - the development of genes that
offset high cholesterol and chronic diseases associated with a meat-rich
diet, according to a new USC study.
Those ancestors also started living longer than ever before - an unexpected
evolutionary twist.

The research by USC professors Caleb Finch and Craig Stanford appeared in
the Quarterly Review of Biology.

"At some point - probably about 2 1/2 million years ago - meat eating became
important to humans," said Stanford, chair of the anthropology department in
the USC College of Letters, Arts and Sciences, "and when that happened,
everything changed."

"Meat contains cholesterol and fat, not to mention potential parasites and
diseases like Mad Cow," he said. "We believe humans evolved to resist these
kinds of things. Mad Cow disease - which probably goes back millions of
years - would have wiped out the species if we hadn't developed
meat-tolerant genes."

Finch, the paper's lead author, and Stanford found unexpected treasure
troves in research ranging from chronic disease in great apes to the
evolution of the human diet. They also focused on several genes, including
apolipoprotein E (apoE), which decreases the risk of Alzheimer's and
vascular disease in aging human adults.

Chimpanzees - which eat more meat than any other great ape, but are still
largely vegetarian - served as an ideal comparison because they carry a
different variation of the apoE gene, yet lack human ancestors' resistance
to diseases associated with a meat-rich diet.

While chimpanzees have a shorter life span compared to humans, they
demonstrate accelerated physical and cerebral development, remain fertile
into old age and experience few brain-aging changes relative to the
devastation of Alzheimer's seen in humans today. Finch and Stanford argued
that the new human apoE variants protected the chimpanzees.

In a series of "evolutionary tradeoffs," the researchers said, humans lost
some advantages over those primates, but gained a higher tolerance to meat,
slower aging and longer lifespan.

Still, if humans developed genes to compensate for a meat-rich diet, why do
so many now suffer from high cholesterol and vascular disease?

The answer is a lack of exercise and moderation, according to the
researchers.

"This shift to a diet rich in meat and fat occurred at a time when the
population was dominated by hunters and gatherers," said Finch, a USC
University Professor and holder of the ARCO-William F. Kieschnick Chair in
the Neurobiology of Aging.

"The level of physical activity among these human ancestors was much higher
than most of us have ever known," he said. "Whether humans today, with our
sedentary lifestyle, remain highly tolerant to meat eating remains an open
question researchers are looking into."

Stanford, co-director of the university's Goodall Research Center, said that
modern-day humans "tend to gorge ourselves with meat and fat."

"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. We can go to the supermarket
and buy as much meat as we want."

"I think we can learn a lesson from this," Stanford said. "Eating meat is
fine, but in moderation and with a lot of exercise."

Contact Gilien Silsby at (213) 740-4751, silsby@usc.edu, or Gia Scafidi at
(213) 740-9335, scafidi@usc.edu.