According to a new study, the origins of modern humans' long-standing love of carbohydrates may predate our existence as a species.
The once stereotype of ancient humans feasting on mammoth steaks and other cuts of meat helped support the idea of a protein-rich diet being necessary for the development of a large brain.
But archaeological evidence in recent years challenges that view, suggesting that humans long ago developed a taste for carbohydrates by roasting things like tubers and other starchy foods, which were discovered by analyzing bacteria lodged in teeth.
The new study, published in the journal Science, is the first evidence of a genetic link to early high-carbohydrate diets. Scientists have 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 for energy. The research reveals that these genes evolved long before the advent of agriculture.
This expansion may even go back hundreds of thousands of years, long before our species Homo sapiens or even Neanderthals emerged as separate human lineages.
Researchers at the Jackson Laboratory in Farmington, Connecticut, and the University of Buffalo, New York, analyzed the genomes of 68 ancient humans. The research team focused on a gene called AMY1, which allows people to identify and begin breaking down the 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.
People today have multiple copies of this gene, and the number varies from person to person. However, it is difficult for geneticists to determine how and when the number of these genes increased - a reflection of when eating starches probably became beneficial to human health.
"The main question we were trying to answer was when did this duplication occur?" That's why we started studying ancient genomes," said the study's first author, Feyza Yilmaz, an associate computer scientist at The Jackson Laboratory.
"Previous research has shown that there is a relationship between the number of copies of AMY1 and the amount of the amylase enzyme that is secreted in our saliva. We wanted to find out if this was a phenomenon that corresponded to the emergence of agriculture. It's a ... burning issue,” she said.
The team found that as early as 45,000 years ago, pre-agricultural hunter-gatherers had an average of four to eight copies of AMY1, suggesting that Homo sapiens had a taste for starch long before the domestication of crops shaped the human diet.
The study also revealed that a duplication of the AMY1 gene was present in the genomes of Neanderthals and Denisovans, an extinct hominin first discovered in 2010 about which relatively little is known. The presence of multiple copies of the gene in the three human species suggests that it was a trait shared by a common ancestor before the different lineages diverged, according to the study.
This finding means that archaic humans had more than one copy of AMY1 as early as 800,000 years ago.
It is not clear exactly when the initial AMY1 duplication occurred, but it probably occurred randomly. Having more than one copy created a genetic capability that gave humans an advantage in adapting to new diets, especially starchy ones, when they encountered different environments.
It's hard to understand how individual genes have changed over time in populations, and the research is "extremely impressive," says Christina Warriner, an associate professor of social sciences and anthropology at Harvard's John L. Loeb University.
"We know that dietary changes have played a major role in human evolution ... but reconstructing these events that occurred thousands, hundreds of thousands, and even millions of years ago is a difficult task," says Warriner.
"The genomic research in this study helps to finally determine the timing of some of these milestones and reveals tantalizing clues about humanity's long love affair with starch," she added. I BGNES
