Managing to Eat Meat Took Getting Used To

Chomping too many fatty steaks is unhealthy for the heart -- but the consequences would be worse if human beings hadn’t evolved special, “meat-adaptive” genes to help manage saturated fat, cholesterol and other hazards of meat-eating, according to two USC scientists.

In a paper published last week in The Quarterly Review of Biology, biologist Caleb E. Finch and anthropologist Craig Stanford said they had identified at least eight genes that might have been key to this important development in human evolution.

Human ancestors probably began eating meat 2.5 million years ago, anthropologists say. In contrast, only the chimps among our nearest relatives, the greater apes, eat meat -- and then only a fraction of what humans do.

In lab studies or in zoos, apes’ cholesterol levels climb more sharply than do humans’ when fed fat, and the animals are more prone to blockages in their coronary arteries. Zoos now know to feed the animals leaner diets.

“Even though we have this idea that we are hypersensitive to cholesterol and fat, the fact is that humans as a species are relatively immune to the harmful effects of these things,” Stanford said.

To pinpoint possible meat-adaptive genes, Finch searched databases and identified eight genes that differed between chimps and humans and which may have had a role in making us meat-tolerant.

One of the genes is called apoE. A particular form of that gene, known as apoE3, evolved in humans some time after the divergence of humans from chimps. ApoE3 is known to help protect human beings against heart disease. It also protects against Alzheimer’s disease.

Finch and Stanford propose that such genes enabled human beings to live longer lives without coming down with chronic diseases: Humans live about 30 years longer than great apes.

The scientists identified seven other genes that they thought helped protect people against infectious agents carried in meat or against an overdose of iron and other metals that are relatively abundant in flesh compared with plants.