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French fries, pasta, bread — we humans love carbs.
But what explains this love for starchy and sugary foods?
The answer might lie in ancient roots.
A new study published in the Science journal on Thursday offers the first hereditary evidence for early carb-laden diets.
Let’s take a closer look.
The study
Researchers based at The Jackson Laboratory in Connecticut’s Farmington and the University of Buffalo in New York analysed the genomes of 68 ancient humans, including one that lived 45,000 years ago.
They focused on a gene called AMY1, which produces an enzyme called amylase.
Amylase helps digest complex carbohydrates from the moment a starchy food enters our mouth. Produced in the salivary glands and the pancreas, it is also the reason why even non-sugary carbs like bread sometimes taste sweet, according to Smithsonian magazine.
Modern humans today have varying numbers of amylase genes in their DNA — some with as many as 11 AMY1 copies per chromosome. These copies appear to be specific to humans. For example, chimpanzees, who also produce amylase, only have a single copy of the gene.
Findings
The genetic foundations of the human ability to digest carbohydrates date back more than 800,000 years, which is significantly earlier than previously believed and predates the development of agriculture.
Despite the fact that our species had not yet developed agriculture, the team’s analysis of ancient human DNA revealed that hunter-gatherers already had an average of four to eight copies of AMY1.
Neanderthals and Denisovans, an extinct hominin first discovered in 2010, about whom relatively little is known, also had duplicate AMY1 genes.
These findings suggest that copies of AMY1 might have originated from a common ancestor approximately 800,000 years ago, prior to the separation of those three species.
The study also discovered that in Peru, where potatoes were domesticated more than 5,000 years ago, the number of additional copies of amylase increased quickly in the last few thousand years.
“The main question that we were trying to answer was, when did this duplication occur? So that’s why we started studying ancient genomes,” the study’s first author Feyza Yilmaz, an associate computational scientist at The Jackson Laboratory, was quoted by CNN.
The majority of the food consumed by early humans was carnivorous. Maybe, in addition to meat, they were also consuming starchy foods. Or perhaps the AMY1 genes were randomly formed without any purpose.
According to Aria Bendix of NBC News, scientists are still unsure of the cause.
“Previous studies show that there’s a correlation between AMY1 copy numbers and the amount of amylase enzyme that’s released in our saliva. We wanted to understand whether it’s an occurrence that is corresponding to the advent of agriculture,” Yilmaz said.
Lead author and a geneticist at the University at Buffalo, Omer Gokcumen, speculated that modern people who have fewer amylase genes may be more vulnerable to diseases like diabetes that are fuelled by a starch-heavy modern diet.
According to him, having more amylase may cause people to produce more insulin, which would increase their absorption of sugar from starch.
The results may eventually suggest amylase-based therapies for various illnesses.
Similar study
Another recent study, published last month in the journal Nature, found that the average number of AMY1 copies in human DNA has increased over the last 12,000 years, corresponding with when humans domesticated and grew crops, including starchy grains and tubers
This suggests that having more copies of AMY1 gave farming humans some kind of advantage and boosted their survival chances.
However, scientists still aren’t sure what that advantage might have been.
One possibility, they think, is that amylase does more than just speed up the breakdown of carbohydrates; it may also help the body get more energy from them, which would have been helpful when food was scarce.
For example, Gokcumen told Carl Zimmer of the New York Times that increasing amylase production might have been a “matter of life and death” during a famine.
Experts opinion
According to CNN, which quoted Taylor Hermes, an assistant professor in the University of Arkansas’s anthropology department who was not involved in the study, the study “provided compelling evidence” of how the molecular machinery for turning indigestible starches into easily accessible sugars evolved in humans.
Furthermore, he pointed out that the latest study published in Science journal supports the growing hypothesis that carbohydrates, not proteins, provide the energy boost required for the gradual enlargement of the human brain.
“The authors finding that an increased copy number 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 gives more credit to the idea that starches were being metabolised into simple sugars to fuel rapidly brain development during human evolution,” Hermes said.
With inputs from agencies