Humans carry multiple copies of a gene that allows us to begin breaking down starch from complex carbohydrates in our mouths, a first step in metabolizing foods like bread and pasta. But when did this gene expansion begin? A new study suggests it was more than 800,000 years ago.
Led by researchers at the University of Buffalo and the Jackson Laboratory for Genomic Medicine, it shows how early duplications of this gene laid the groundwork for the wide genetic variation that still exists today and influences how efficiently humans digest starchy foods.
“If you’ve ever had trouble cutting back on carbs, ancient DNA could be to blame,” the lab said in a statement.
The results of the research are published in the journal Science and reveal that the duplication of the gene in question – known as the salivary amylase gene ( AMY1 ) – may not only have helped shape human adaptation to starchy foods, but may have occurred long before the arrival of agriculture.
“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 of the University at Buffalo. Amylase is an enzyme that not only breaks down starch into glucose, but also gives bread its flavor.
To reach their conclusions, the team, also led by Charles Lee, used advanced genomic techniques to map the AMY1 gene region in extraordinary detail.
Analyzing the genomes of 68 ancient humans, including a 45,000-year-old sample from Siberia, she 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 roaming Eurasia with a wide variety of high AMY1 copy numbers long before they began domesticating plants and eating excessive amounts of starch.
“This suggests that the AMY1 gene may have first duplicated more than 800,000 years ago, long before humans diverged from Neanderthals and much earlier than previously thought,” said Kwondo Kim of the Jackson Laboratory.
Gokcumen adds: “The initial duplications in our genomes laid the groundwork 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.”
The research also highlights the impact of agriculture on AMY1 variation .
While early hunter-gatherers had multiple copies of the gene, European farmers experienced an increase in the average copy number of AMY1 over the past 4,000 years, likely due to their starch-rich diets.
Furthermore, Gokcumen’s previous research had shown that domesticated animals that cohabit with humans, such as dogs and pigs, also had higher copy numbers of AMY1 compared to animals that do not rely on starch-rich diets.