Nowadays, carbohydrates are often demonized as unhealthy fattening foods. Long-chain sugar compounds drove human evolution. Success is in the genes – and US researchers have now discovered how it came about.
Whether bread, pasta, corn, potatoes or rice: when chewed, these foods develop a pleasant sweetness in the mouth. And the great love of starchy food is apparently an ancient legacy: Humanity developed it more than 800,000 years ago because carbohydrates brought with them some advantages. At least that is what a study by US researchers suggests, the results of which have now been published in the specialist magazine “Science”.
The enzyme amylase is responsible for breaking down complex “starch chains” into short sugar molecules. This occurs in the mouth and is also produced by the pancreas, correspondingly the gene AMY1 or the gene AMY2 is called up.
The blueprint for this enzyme is anchored in several genes in the genome of humans and certain monkeys, each of which can have several copies. Their number shapes Incidentally, other mammals are also very different; mice and dogs, for example, are well equipped, but cats and whales are not.
It has been known for years that humans have more amylase gene copies than chimpanzees or gorillas. But when and why did this difference emerge? And why do people differ depending on their region? Scientists are grappling with these and other questions about human evolution, and now they can answer some of them.
“The idea is that the more amylase genes you have, the more amylase you can produce and the more starch you can effectively digest,” explains evolutionary biologist Omer Gokcumen in a statement on the current study Studyin which he was involved with his team at the University of Buffalo.
Amylase is an enzyme that not only breaks down starch into glucose, emphasizes Gokcumen, but also gives bread its – seductive – taste. It was therefore previously assumed that the number of amylase gene copies only increased with the advent of agriculture, thanks to grain products.
The study authors now used various sequencing methods to trace the origins of the salivary amylase gene AMY1 as precisely as possible. The genomes of 98 people from today, but from different regions, were examined. These sequences were then compared with the genetic information of 68 archaic representatives, including Neanderthals and Denisovans. Among the samples analyzed was a 34,000-year-old one from Romania and a 45,000-year-old one from Siberia.
The comparisons showed, among other things, that several copies of the gene were present in early hunter-gatherer cultures before the advent of agriculture. For example, the AMY1 gene was present eight times in the Romanian sample and six times in the Siberian sample. Long before people in Eurasia grew grains and other starchy crops and bred higher-yielding varieties, they had four to eight AMY1 copies.
But the European samples reflect an evolutionary trend: During the “Neolithic Revolution,” when hunter-gatherers became sedentary farmers, the number of AMY1 copies increased sharply over the past 4,000 years. Which is probably related to the starch-rich diet of farming cultures.
“Individuals with a higher number of AMY1 copies were probably able to digest starch more efficiently – and they had more offspring,” says Gokcumen, summarizing the development. This diet appeared to be a survival advantage: “Over a long evolutionary period, their lineages ultimately performed better than those with lower copy numbers, thereby increasing the number of AMY1 copies.”
Up to 20 gene copies
This observation fits with the results of a recent study in the journal Nature. published Study led by scientists at the University of California at Berkeley. They examined the genome data of 5,600 people from all over the world, from present and past times, in order to understand amylase evolution.
Up to 20 copies of AMY1 were found; The cell nuclei of people in Oceania, South and East Asia are particularly well populated. In the case of the AMY2 gene, of which A and B versions exist, the documented range is from zero to six copies, or two to seven.
A closer look at the data from Europe revealed that the average number of amylase gene copies here has increased so significantly over the past 12,000 years that the researchers speak of “positive selection”. They describe the variation in the copy number of all three genes as “typically human”.
In the current study, the scientists found that even in the Neanderthal and Denisovan genomes they examined, there were already several copies of the amylase blueprint. “This suggests that the AMY1 gene may have been first duplicated more than 800,000 years ago,” said Kwondo Kim of the Jackson Laboratory for Genomic Medicine (JAX), in Farmington, Connecticut. So even before the lines of Neanderthals and Homo sapiens separated – and much earlier than previously assumed.
“The first duplications in our genomes laid the foundation for critical variations in the amylase region, allowing humans to adapt to changing diets as starch consumption increased dramatically with the advent of new technologies and lifestyles,” adds Gokcumen.
In fact, the flexibility in the number of AMY1 copies offered an advantage for adapting to new diets – particularly those rich in starch. And the first duplication of AMY1 created a genetic opportunity that would later shape the species Homo sapiens. Over the course of thousands of years, it has spread across all continents and has had to adapt to a wide variety of living conditions.
Previous research by Gokcumen suggests that evolutionary changes related to amylase may have arisen independently in different animal species. Both the duplications of the amylase gene and the ability to produce amylase in saliva. Scientists call this phenomenon convergent evolution; it usually signals a particularly useful adaptation.
“Given the key role that AMY1 copy number variation plays in human evolution, this genetic variation provides an exciting opportunity to explore its impact on metabolic health,” notes JAX researcher Feyza Yilmaz.
The mechanisms involved in starch digestion and glucose metabolism can also be revealed. Future studies on the effects and timing of selection could provide crucial insights into human genetics, nutrition and health.
As head of department, Sonja Kastilan is dedicated to “knowledge” – and pursues topics from medicine and life sciences: from Aids from evolutionary biology and genetic analysis to stem cells and Zika.
with dpa
