What came first, farming or our ability to digest its carbohydrate-rich harvest?

A study of a gene key to breaking down carbohydrates started duplicating itself in humans over 800,000 years ago— well before the dawn of agriculture. A team of researchers report in Science that the gene, called AMY1, started creating variations of itself long before humans split from neanderthal. It plays an essential role in producing starch-digesting saliva.

Ancient Dietary Needs

In general, when genes make “copy variations” of themselves, it indicates an increased focus on the function of the original gene. The proliferation of AMY1 variants back then provides a snapshot of the ancient human diet — and indicates how it changed when hunter-gathers shifted to farming.

The researchers analyzing the genomes of 68 ancient humans, including a 45,000-year-old sample from Siberia. They found that pre-agricultural hunter-gatherers already had an average of four to eight AMY1 copies per cell. That number of copies suggests that humans’ genes were a bit ahead of their bodies’ changing dietary needs. Humans only started farming about 12,000 years ago, but the number of AMY1 copies showed that our DNA was preparing us to eat more plants over 30,000 years before the dawn of agriculture.

Read More: Early Humans Didn’t Follow A Diet, They Ate For Survival

Adapting to a Carb-Rich Diet

Evolution almost certainly played a role in the number of that gene’s copy variations, which grew over time.

“The duplication potentially occurred as an ‘adaptation response,’” says Kwondo Kim, an author of the study, who works at the Jackson Laboratory for Genomic Medicine (JAX) in Connecticut. She suspects that early humans found starches as part of their foraging, and their bodies slowly adapted to this dietary shift, because AMY1 helps turn starch to energy. “This helped transition humans to an agricultural lifestyle,” says Kim.

That theory tracks with the group’s data. For example, genetic information from European farmers shows a surge in the average number of AMY1 copies over the past 4,000 years. That data says that as that group ate more carbs, their bodies developed more metabolic tools to process them.

Read More: Humans Roasted Starchy Carbs 170000 Years Ago

How the AMY1 Gene Variation Impacts Our Metabolism Today

Although nailing down AMY1 copies in early humans has been rather concrete, understanding what the numbers mean in today’s population is muddier. Some studies link high AMY1 copy numbers to diabetes. “This is a controversial topic, because some studies say there is no correlation,” says Kim.

There is also more work to be done in understanding how AMY1 copy numbers affect enzyme levels, insulin levels, and relationship to Body Mass Index. But again, several studies have shown conflicting results.

“Given the key role of AMY1 copy number variation in human evolution, this genetic variation presents an exciting opportunity to explore its impact on metabolic health and uncover the mechanisms involved in starch digestion and glucose metabolism,” Feyza Yilmaz, an associate computational scientist at JAX and a lead author of the study, said in a press release. “Future research could reveal its precise effects and timing selection, providing critical insights into genetics, nutrition, and health.”

Read More: How Are Humans Still Evolving?

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Before joining Discover Magazine, Paul spent over 20 years as a science journalist, specializing in U.S. life science policy and global scientific career issues. He began his career in newspapers, but switched to scientific magazines. His work has appeared in publications including Science News, Science, Nature, and Scientific American.