Humans in Europe have dramatically increased their ability to digest carbohydrates over the past 12,000 years, increasing the number of genes for starch-digesting enzymes from an average of eight to more than 11.
The speed of evolution that led to the corresponding changes in genes turned out to be 10 thousand times higher than the speed of change of one pair of DNA bases in the human genome. This is evidenced by the results of research by scientists from the University of California (USA), reports the publication EurekAlert.
The increase in the number of genes encoding these enzymes coincides with the spread of agriculture into Europe from the Middle East, and with it an increasingly starchy human diet rich in high-carbohydrate foods such as wheat and other grains.
Having more copies of genes usually means higher levels of the protein they code for — in this case, the enzyme amylase, produced in saliva and the pancreas to break down starch into sugar, which provides the body with energy, the paper notes.
The researchers also found evidence of an increase in amylase genes in other farming populations around the world, and that the region of chromosomes where these amylase genes are located appears similar in all of these populations, regardless of which specific starchy plant domesticated the crop.
The findings show that as agriculture emerged independently around the world, it appears to have rapidly altered the human genome in nearly identical ways across populations to deal with increasing carbohydrates in the diet, the paper notes.
The genomes of chimpanzees, bonobos, and Neanderthals all have a single copy of a gene on chromosome 1 that codes for salivary amylase, called AMY1. The same is true for two pancreatic amylase genes, AMY2A and AMY2B. These three genes are located near each other in a region of the primate genome known as the amylase locus.
However, human genomes contain very different numbers of amylase genes. Previously, scientists were unable to completely sequence this locus – traditional sequencing methods could not distinguish between copies of the genes.
New research technologies have shown that each copy of the human genome contains:
- from one to 11 copies of AMY1;
- from zero to three copies of AMY2A;
- from one to four copies of AMY2B.
The number of copies correlates with gene expression and protein levels, and therefore with the ability to digest starch, the scientists note.
The study also found that:
- About 12,000 years ago, people in Europe had an average of about four copies of the salivary amylase gene – now that number has increased to seven;
- the combined copy number of the two pancreatic amylase genes also increased by an average of half a gene during this time;
- the primary duplication event occurred long before the rise of agriculture – 280 thousand years ago, adding two copies of AMY1 to the human genome;
- Such changes in the genome could make people more vulnerable to tooth decay—having more copies of AMY1 helps saliva better convert starch from chewed food into sugar, which feeds tooth-eroding bacteria.
If you take a piece of dry pasta and put it in your mouth, over time it will become sweet, scientists note. – It is the enzyme amylase in your saliva that breaks down starch into sugar. This happens in all humans, as well as other primates.
Source: EurekAlert
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I am David Wyatt, a professional writer and journalist for Buna Times. I specialize in the world section of news coverage, where I bring to light stories and issues that affect us globally. As a graduate of Journalism, I have always had the passion to spread knowledge through writing.