The ability to digest starch began 800,000 years ago and changed the human diet

A group of researchers has identified the moment when the first duplication of the gene for salivary amylase (AMY1) occurred, which helps break down starch in the mouth, which is the first step in metabolizing foods such as bread and pasta . According to what they say this Thursday in the magazine ‘Science’, This change, which has influenced our diet to this day, occurred at least 800,000 years ago, long before the advent of agriculture.

Researchers have long known that humans carry multiple copies of AMY1. However, until now it has been extremely difficult to identify how and when the number of these genes expanded. The new study, led by the University at Buffalo (UB) and the Jackson Laboratory (JAX), shows how early duplications of this gene laid the foundation for the wide genetic variation that still exists today, influencing efficacy with which humans digest starchy foods.

“The idea is that the more amylase genes you have, the more amylase you can produce and the more starch you can digest efficiently,” explains Omer Gokcumen, professor in the Department of Biological Sciences at the UB Faculty of Arts and Sciences. Amylase, the researchers explain, is an enzyme that not only breaks down starch into glucose, but also gives bread its flavor.

By analyzing the genome of 68 ancient humans, including a 45,000-year-old sample from Siberia, the research team found that pre-agricultural hunter-gatherers already had an average of four to eight copies of AMY1 per diploid cell, suggesting that Humans were already walking around Eurasia with a wide variety of high AMY1 copy numbers long before they began domesticating plants and eating excessive amounts of starch.

Also in Neanderthals

The study also found that duplications of the AMY1 gene occurred in neanderthals and Denisovans. “This suggests that the AMY1 gene may have first duplicated more than 800,000 years ago, long before humans split from Neanderthals and much earlier than previously thought,” said Kwondo Kim, one of the lead authors. from this study from the Lee Laboratory at JAX.

“The initial duplications in our genomes laid the foundation for significant variation in the amylase region, allowing humans to adapt to changing diets as starch consumption increased dramatically with the advent of new technologies and lifestyles.” » explains Gokcumen.

According to the researchers, the initial duplication of AMY1 was like the first ripple in a pond, creating a genetic opportunity that later shaped our species. As humans expanded across different environments, flexibility in AMY1 copy number provided an advantage in adapting to new diets, particularly those high in starch.

“After the initial duplication, which gave rise to three copies of AMY1 in one cell, the amylase locus became unstable and began to generate new variations,” says Charikleia Karageorgiou, one of the main authors of the study at the UB. “From three copies of AMY1, you can obtain up to nine copies, or even return to one copy per haploid cell.”

Even in domestic animals

The research also highlights how agriculture affected AMY1 variation. While early hunter-gatherers had multiple gene copies, European farmers saw an increase in the average copy number of AMY1 over the past 4,000 years, likely due to their starchy diets. Gokcumen’s previous research showed that domestic animals that live alongside humans, such as dogs and pigs, also have higher copy numbers of AMY1 compared to animals that do not rely on high-starch diets.

“It is likely that individuals with a higher copy number of AMY1 digested starch more efficiently and had more offspring,” Gokcumen suggests. “Ultimately, their lineages performed better over a long evolutionary period than those with lower copy numbers, which spread the copy number of AMY1.”

The findings are consistent with a study led by the University of California, Berkeley, published last month in ‘Nature’, which found that humans in Europe expanded their average number of AMY1 copies from four to seven over the last 12,000 years.

“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.” » says Feyza Yilmaz, associate computational scientist at JAX and lead author of the study. “Future research could reveal their precise effects and timing, providing critical information about genetics, nutrition and health.”