() – The origin of modern humans’ ancient love for carbohydrates may predate our existence as a species, according to a new study.
A once-prevailing stereotype that ancient humans feasted on mammoth fillets and other pieces of meat helped foster the idea of a protein-rich diet, necessary to fuel the development of a large brain. size.
But archaeological evidence in recent years has challenged this view, suggesting that humans long ago developed a taste for carbohydrates, roasting things like tubers and other starch-laden foods that have been detected by analyzing the bacteria lodged in teeth.
The new investigation, published on Thursday in the academic journal Science, provides the first hereditary evidence for early carbohydrate-laden diets. Scientists traced the evolution of a gene that allows humans to more easily digest starch, breaking it down into simple sugars that our bodies can use as a source of energy. The study revealed that these genes were duplicated long before the advent of agriculture.
This expansion could even date back hundreds of thousands of years, long before our species, the Homo sapiensor even Neanderthals emerged as distinct human lineages.
Researchers at the Jackson Laboratory in Farmington, Connecticut, and the University at Buffalo in upstate New York analyzed the genomes of 68 ancient humans. The study team focused on a gene called AMY1, which allows humans to identify and begin breaking down complex carbohydrate starch in the mouth by producing the enzyme amylase. Without amylase, humans would not be able to digest foods such as potatoes, pasta, rice or bread.
Today, humans have several copies of this gene, and the number varies from person to person. However, it has been difficult for geneticists to figure out how and when the number of these genes expanded, a reflection of when eating starch probably became advantageous for human health.
“The main question we were trying to answer was: when did this duplication occur? That’s why we started studying ancient genomes,” explained the study’s first author, Feyza Yilmaz, an associate computer scientist at the Jackson Laboratory.
“Previous studies show that there is a correlation between the number of copies of AMY1 and the amount of amylase enzyme that is released into our saliva. We wanted to understand if it is a fact that corresponds to the arrival of agriculture. “This is… a controversial issue,” he said.
The team found that 45,000 years ago, hunter-gatherers whose lifestyle predated agriculture had an average of four to eight copies of AMY1, suggesting that the Homo sapiens had a taste for starch long before crop domestication shaped the human diet.
The research also revealed that the AMY1 gene duplication existed in the genomes of Neanderthals and Denisovans, an extinct hominid first discovered in 2010 about which relatively little is known. The presence of multiple copies of the gene in three human species suggests that it was a trait shared by a common ancestor, before the different lineages separated, according to the study.
That finding means that ancient humans had more than one copy of AMY1 as early as 800,000 years ago.
It is not clear exactly when the initial duplication of AMY1 occurred, but it probably occurred randomly. The presence of more than one copy created a genetic opportunity that gave humans an advantage in adapting to new diets, especially starchy ones, as they encountered different environments.
The analysis also showed that the number of copies of AMY1 carried by a person increased sharply over the last 4,000 years, probably favored by natural selection as humans adapted to the starch-rich diets resulting from the change in a lifestyle. from hunter-gatherer life to agriculture and cereal cultivation.
The study “provided compelling evidence” for how the molecular machinery to convert hard-to-digest starches into easily accessible sugars evolved in humans, said Taylor Hermes, an associate professor in the department of anthropology at the University of Arkansas, who was not involved in the study. investigation.
What’s more, the new research reinforces the emerging theory that it was carbohydrates, and not proteins, that provided the energy supply necessary for the increase in human brain size over time, he said.
“The authors’ finding that higher copy numbers of the amylase gene, which results in a greater ability to break down starch, may have emerged hundreds of thousands of years before Neanderthals or Denisovans lends further credence to the idea that starches were metabolized into simple sugars to fuel rapid brain development during human evolution,” Hermes said.
“While I think further testing with higher quality ancient human genomes is warranted, I was surprised that the authors were able to detect multiple copies of amylase genes in previously published Neanderthal and Denisovan genomes,” Hermes added. “This demonstrates the value of continuing to explore the genomes of our human ancestors for important medical and physiological records.”
Understanding how individual genes varied over time in populations is challenging, and the study is “extremely impressive,” said Christina Warinner, John L. Loeb Associate Professor of Social Sciences and Anthropology at Harvard University.
“We know that dietary changes have played a central role in human evolution… but piecing together these events that took place thousands, hundreds of thousands, even millions of years ago is daunting,” said Warinner, who was not involved in the research.
“The genomic investigations from this study are helping to finally mark the time of some of those big milestones, and are revealing promising clues about humanity’s long love affair with carbohydrates.”
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