Can’t Get Enough Carbs? That Craving Might Have Started More Than 800,000 Years Ago

From crispy French fries to crusty sourdough loaves, carbs are an integral (and delicious) part of the human diet.

But why do we love these starchy and sugary foods? The answer might be embedded in our DNA, according to a new study published Thursday in the journal Science.

Scientists have traced the genetic underpinnings of our ability to digest carbs to more than 800,000 years ago, long before the advent of agriculture—and much earlier than previously thought.

This finding raises new questions around our hunter-gatherer ancestors’ diet and lifestyle. It also challenges the long-held belief that a protein-rich diet was responsible for the increase in human brain size, scientists suggest. Perhaps carbs, not meat, gave humans the energy needed for developing bigger brains.

“We know that dietary shifts have played a central role in human evolution … but reconstructing these events that took place thousands, hundreds of thousands and even millions of years ago is daunting,” says Christina Warinner, an anthropologist at Harvard University who was not involved with the research, to CNN’s Katie Hunt. “This study’s genomic sleuthing is helping to finally time stamp some of those major milestones, and it is revealing tantalizing clues about humanity’s long love affair with starch.”

Researchers studied the genomes of 68 ancient humans, including one that lived 45,000 years ago. More specifically, they focused on a gene called AMY1, which is responsible for the production of an enzyme called amylase.

Amylase helps humans digest complex carbohydrates, starting from the moment a starchy food enters the mouth. Amylase, which is produced in the salivary glands and the pancreas, is also the reason why even non-sugary carbs like bread sometimes taste sweet.

Today’s modern humans have varying numbers of amylase genes in their DNA—some people have as many as 11 AMY1 copies per chromosome. These copies seem to be specific to humans: Chimpanzees, for example, also produce amylase, but they only have a single copy of the gene.

When the team looked at ancient human DNA, they found that hunter-gatherers already had four to eight copies of AMY1, on average, even though our species had not yet developed agriculture. Neanderthals and Denisovans, early human relatives, also had duplicate AMY1 genes.

These findings indicate that copies of AMY1 may date back to a common ancestor some 800,000 years ago, before those three species split off from one another. But why did early humans—who primarily ate a carnivorous diet—have the amylase gene? Perhaps they were also eating starchy foods, in addition to meat. Or maybe the AMY1 genes developed randomly and served no purpose at all. Scientists still aren’t sure of the reason, reports NBC News’ Aria Bendix.

Another recent study, published last month in the journal Nature, finds that the average number of AMY1 copies in human DNA has increased over the last 12,000 years—a timeline that corresponds with when humans began domesticating and growing crops, many of which were starchy grains and tubers.

This finding seems to suggest that having more copies of AMY1 gave farming humans some kind of advantage that helped boost their chance of survival. But scientists aren’t sure what that advantage might have been. One possibility is that amylase does more than just kickstart the digestion of carbs—maybe it also helps the human body extract more energy from carbs, which would have been useful during times of food scarcity.

During a famine, for instance, producing more amylase may have been a “matter of life and death,” says Omer Gokcumen, a geneticist at the University at Buffalo and a co-author of the Science study, to the New York Times’ Carl Zimmer.

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Sarah Kuta is a writer and editor based in Longmont, Colorado. She covers history, science, travel, food and beverage, sustainability, economics and other topics.