The Evolution of Diet

Scientists still have plenty of unanswered questions about the origins and evolution of human meat-eating, but there are some strong theories as to when, how and why we started to incorporate larger amounts of meat in our omnivorous diet.

Between 2.6 and 2.5 million years ago, the Earth got significantly hotter and drier. Before that climate shift, our distant human ancestors—collectively known as hominins—were subsisting mostly on fruits, leaves, seeds, flowers, bark and tubers. As the temperature rose, the lush forests shrank and great grasslands thrived. As green plants became scarcer, evolutionary pressure forced early humans to find new sources of energy. Our ancient hominin ancestors weren’t capable hunters yet, but likely scavenged the meat from fallen carcasses. Once humans shifted to even occasional meat eating, it didn’t take long to make it a major part of our diet. Zaraska says there’s ample archaeological evidence that by 2 million years ago the first Homo species were actively eating meat on a regular basis. 

The grassland savannas that spread across Africa supported growing numbers of grazing herbivores. Archaeologists have found large herbivore bones dating from 2.5 million years ago with telltale cut marks from crude stone tools. Our ancient hominin ancestors weren’t capable hunters yet, but likely scavenged the meat from fallen carcasses.

While our ancient human relatives had stronger jaws and larger teeth than modern man, their mouths and guts were designed for grinding up and digesting plant matter, not raw meat. Even crude stone tools could function as a second set of teeth, stripping hunks of flesh from a zebra carcass or bashing open bones and skulls to get at the nutrient-rich marrow or brains inside. By pre-processing meat with tools originally designed to dig tubers and crack open nuts, our ancestors made animal flesh easier to chew and digest.

Meat was the original ‘brain food.’

When ancient hominins subsisted exclusively on fruits, plants and seeds, they expended a lot more energy on digestion. Millions of years ago, the human gut was longer and slower, requiring more effort to derive limited calories from forage foods. With all of that energy being spent on digestion, the human brain remained relatively small, similar to other primates today. 

When humans began adding meat to their diet, there was less of a need for a long digestive tract equipped for processing lots of plant matter. Slowly, over hundreds of thousands of years, the human gut shrunk. This freed up energy to be spent on the brain, which grew explosively in size.

When humans began cooking meat, it became even easier to digest quickly and efficiently, and capture those calories to feed our growing brains. The earliest clear evidence of humans cooking food dates back roughly 800,000 years ago, although it could have begun sooner.

Humans continue to eat meat because we like it, not because we need it.

Meat was clearly pivotal in the evolution of the human brain, but that doesn’t mean that meat is still an irreplaceable part of the modern human diet. Zaraska says any calorie-dense food would have had the same effect on our ancient evolving brains—“it could have been peanut butter”—but that meat happened to be available.

We crave meat today, in part, because our brains evolved on the African savanna and are still wired to seek out energy-dense sources of protein. It’s similar to our penchant for sugar, a rare calorie-rich commodity to our foraging ancestors whose brains rewarded them for finding ripe fruit. 

But we also crave meat because of its cultural significance. Different cultures are more or less meat-centric, although there’s a clear correlation between wealth and meat consumption. Industrialized Western nations average more than 220 pounds of meat per person per year, while the poorest African nations average less than 22 pounds per person. 

An overly meaty diet has been linked to heart disease, diabetes and certain cancers—things our distant ancestors never had to worry about, because they didn’t live long enough to fall victim to chronic disease. “The goals of life for our ancestors was very different than ours,” says Zaraska. “Their goal was to survive to the next day.”

For the full article, visit https://www.history.com/author/dave-roos

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