Our bodies absolutely need carbohydrates for energy. It’s a matter of survival. So some human populations have actually increased the number of genes that break down starch and sugars over the last 12,000 years. During that time, Europeans increased their starch-breaking genes from an average of 8 to more than 11.
This adaptation reflects a shift from a hunter-gatherer lifestyle to a more agricultural one as agriculture spread from the Middle East to Europe. High-carbohydrate staples such as wheat increased dramatically in the human diet, making their ability to absorb energy efficiently advantageous. The study was published in the journal Nature on September 4th. Nature.
Focus on the “amylase locus”
Some There are approximately 19,900 known genes in the human genome. Can produce the specific protein that a gene codes for enzymeEnzymes have various functions, amylase Amylase helps your body break down carbohydrates. It is produced in your saliva and pancreas and helps digest starches into sugars that give your body energy.
“When you put dry pasta in your mouth, over time it becomes a little sweeter,” says study co-author Peter Sudmant, a biologist at the University of California, Berkeley. It said in a statement“This is where the amylase enzyme in saliva breaks down starch into sugar. This happens in all humans, and also in other primates.”
[Related: Is butter a carb?]
More copies of a gene usually means that an organism has higher levels of the protein that a particular gene codes for. enzymeBonobos, chimpanzees and Neanderthals have one copy of the gene in their genomes. Amy 1This gene on chromosome 1 codes for salivary amylase. Their genome also contains one copy each of the two pancreatic amylase genes. AMY2A and AMY2BThese three genes are what scientists call ” Amylase locusBut the human genome is a bit different.
“Our study found that each copy of the human genome contains one to 11 copies of AMY1, zero to three copies of AMY2A, and one to four copies of AMY2B,” says study co-author Runyang Nicholas Lu, a postdoctoral researcher at the University of California, Berkeley. It said in a statementt. “Copy number correlates with gene expression, protein levels, and the ability to digest starch.”
Using genetic analysis, the team found that humans across Europe had evolved around 12,000 years ago. 4th division average The number of salivary amylase genes increased over time to about seven. The copy numbers of the two pancreatic amylase genes also increased by an average of half a gene. This increase in carbohydrate genes was due to A powerful survival advantage They have a chromosome that contains multiple copies of the amylase gene.
Lifestyle changes
Importantly, the research team also Amylase gene increase in other agricultural populations around the worldThe chromosomal regions in which these amylase genes are located also appear to be similar in all of these populations, regardless of what starchy plants were domesticated in that culture.
According to the teamThis shows that when agriculture began among people around the world, they rapidly changed the human genome in incredibly similar ways to take advantage of increased access to carbohydrates. The rate of evolution leading to changes in the copy number of the amylase gene was about 10,000 times faster than the rate of single DNA base pair changes in the human genome.
[Related: Love corn? Thank interbreeding.]
“It has long been thought that the copy number of amylase genes in Europeans has increased since the beginning of agriculture, but until now we have never been able to fully sequence this locus, which is extremely repetitive and complex,” says Sudmant. “Now we finally have a complete view of this structurally complex region, which allows us to investigate its selection history, evolutionary timing, and diversity in people around the world. Now we can start to think about its relevance to human disease.”
One suspected link is tooth decay: previous studies have suggested that people with more copies of AMY1 are more likely to develop cavities, possibly because saliva is better at converting starches in chewed food into sugars that feed tooth-eating bacteria.
Long-read sequencing
The study also made use of a technique called gene sequencing. Long-read sequencingThis allows scientists to read DNA sequences thousands of base pairs long and figure out exactly where the repetitive sequences are located.
At the time of the study, Human Pan-Genome Reference Consortium The Human Ploidy Research Center (HPRC) collected long-read sequences of 94 human haploid genomes. The team used these genomes to assess diversity in the modern amylase region. They then assessed the same region in 519 ancient European genomes. Using the HPRC genomes (called the pangenome) provided a more comprehensive reference and a more accurate picture of human diversity.
“These findings suggest that the microbial communities of the human body are important in the development of microbial communities,” said study co-author Joana Rocha, a postdoctoral researcher at the University of California, Berkeley. The region where amylase genes are densely packed“A sculpture made of different Lego blocks: that’s what a haplotype structure is. Previous studies had to first dismantle the sculpture and infer what it looked like from the pile of bricks. Long-read sequencing and pangenomics methods now allow us to look at the sculpture directly, which gives us unprecedented power to study the evolutionary history and selective effects of different haplotype structures.”
[Related: The final missing piece of the human genome has been decoded.]
Scientists can use long-read sequencing to explore other regions of the genome, including those that are relevant to our cells. Immune system, skin pigmentation, mucus productionAll of these spots underwent rapid genetic duplication in recent human history.
“One of the exciting things we’ve been able to do here is look at both modern and ancient genomes to analyze the structural evolutionary history of this locus,” says study co-author Eric Garrison, a computational biologist at the University of Tennessee Health Science Center. He said in a statement.
These methods could also be applied to other species, especially those that are often around humans: Dogs, pigs, rats and mice all have more copies of the amylase gene than their wild relatives and are more likely to make use of our table scraps and garbage.
