He superpower that allows us humans to begin processing the starch in food with our saliva was created much earlier than we thought, according to a work published this Thursday in the magazine Science.
An investigation led by Omer Gokcumenfrom the University at Buffalo (UB), places the origin here revolution metabolism more than 800,000 years ago, when the doubling of the salivary amylase gene (AMY1), which facilitates this ability, prepared the ground for human adaptation to starchy foods, which we began to consume en masse much later, after the Neolithic revolution and the cultivation of cereals.
While the rest of animals have to wait for the carbohydrates to reach the stomach and for the enzyme amylase, secreted by the pancreas, to break them down into smaller sugars, our species expresses this enzyme in saliva and we begin the digestion of starch in the mouth. This explains why if we leave a piece of bread on our tongue we notice a sweet taste, a capacity whose origin scientists placed at the beginning of agriculture, about 10,000 years ago, and which is also present in our petsexposed to the same starch-rich diets as us.
Matured on a slow ‘fire’
The new work was based on the analysis of the genomes of 68 ancient human remains, including a 45,000-year-old sample from Siberia. The authors have found that pre-agricultural hunter-gatherers already had an average of four to eight copies of AMY1suggesting that humans were already walking around Eurasia with a wide variety of high copy numbers of this gene long before they began domesticating plants and eating excessive amounts of starch.
The study also indicates that gene duplications occurred AMY1 in Neanderthals and Denisovans, leading them to conclude that this key change happened long before our species split from the Neanderthals and to give the figure of at least 800,000 years. “The initial duplications in our genomes laid the foundation 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.” ”says Gokcumen.
This observation is consistent with the availability of cooked starch among archaic hominids, made possible by their learning to use fire.
It is difficult to establish the cause of these early changes, but the authors believe that these initial duplications before the split between humans, Neanderthals and Denisovans may have had to do with the use of fire to heat food. “This observation is consistent with recent evidence of starch consumption by Neanderthals, and perhaps with the availability of cooked starch among archaic hominids, made possible by their learning to use fire,” they write.
How to throw a stone into a pond
The researchers believe that the initial duplication of AMY1 It was like the first ripple that spreads after throwing a stone into a pond: it created a genetic opportunity that was later fundamental for our species. As humans expanded across different environments, flexibility in gene copy number provided an advantage in adapting to new diets, particularly those high in starch. “After the initial duplication, which resulted in three copies of AMY1 in a cell, the locus of amylase became unstable and began to generate new variations,” explains Charikleia Karageorgiouone of the main authors of the study. From three copies of AMY1you can obtain up to nine copies, so when the Neolithic revolution arrived that change was already underway.
The new research also documents how agriculture affected the variation of AMY1 in European farmers, who saw an increase in the average number of copies of the gene over the last 4,000 years, probably due to their starchy diets. A result that agrees with the previous research of Gokcumen, in which he showed that domestic animals such as dogs and pigs also have a higher number of copies of AMY1 compared to animals that do not rely on starchy diets.
It is likely that individuals with a higher number of copies of ‘AMY1’ digested starch more efficiently and had more offspring
Omer Gokcumen
— Researcher at the University at Buffalo (UB) and lead author of the study
From that moment on, evolution did the rest. “It is likely that individuals with a higher number of copies by AMY1 digest starch more efficiently and have more offspring,” says Gokcumen. “Ultimately, their lineages performed better over a long evolutionary period than those with lower copy numbers, which spread the copy number of AMY1.”
Why do we eat potatoes and cereal?yes
For Gemma Marfanyprofessor of Genetics at the University of Barcelona (UB), the genomic analysis is very well worked out at a methodological level, given that the genomic region that contains the amylase genes, being duplicated and with very homologous sequences, is not easy to align and analyze. “The presence of this amylase gene, necessary to degrade starch, helped us digest and take good advantage of plants rich in carbohydrates that provide us with energy, such as potatoes and other tubers, rice, wheat and other cereals. ”, he points out. In his opinion, “expressing more amylase in saliva gave our ancestors an advantage over having only one copy of the gene.” AMY1as chimpanzees and gorillas have and, later, with the appearance of agriculture and domestication of cereals, this pressure of natural selection increased even more.”
“The amylase gene is a clear example of genetic evolution in response to diet, similar to the case of the lactase gene, which shows one of the most marked signs of positive selection in our DNA,” he explains. Antonio Salasgeneticist at the University of Santiago (USC). In his opinion, this work represents a considerable technical challenge, in addition to the bioinformatics and evolutionary analysis effort necessary to understand this variability. “The authors provide evidence that variations in the number of copies of the gene AMY1 coincide with the changes necessary for the transition from nomadic hunter-gatherer societies to sedentary agricultural societies, although one of the remaining challenges is to understand the exact physiological mechanism through which variability in the number of copies of the gene confers an adaptive advantage, especially in different cultural contexts with significant dietary variability,” he highlights.
“What the authors deduce from their study is that the first duplications could have occurred before the divergence of modern humans, Neanderthals and Denisovans,” says the Spanish paleoanthropologist and academic. José María Bermúdez de Castro. “This divergence has been estimated between 550,000 and 765,000 years, although some authors take it back in time to 800,000 years, and this is the date used by the authors of the work.” Since there is evidence of the use of fire for cooking at a site in Israel (Daughters of Jacob Bridge), dated to approximately 780,000 years, the authors consider that the use of fire for cooking – which allows food to be digested better – could have influenced the duplication of the gene AMY1he points out.
The ability to ingest starch from cooked tubers thanks to these duplications could also be related to an increase in cranial capacity.
Carles Lalueza-Fox
— Ancient DNA specialist
These conclusions point to a fascinating possibility, which is that learning to handle fire led to a change in our saliva and opened the door through which the subsequent agricultural revolution ended up taking place. “It is an interesting hypothesis, because the ability to ingest starch from cooked tubers thanks to these duplications could also be related to an increase in cranial capacity,” adds the ancient DNA specialist. Carles Lalueza-Fox. Although there were other previous works on this gene that proposed duplications after the separation of modern humans and Neanderthals, remember, the most relevant thing is that here they find a certain variability in the archaic genomes and propose an earlier date. “And there is a beautiful parallel story,” he points out, “and that is that duplications of this gene are also found in dogs and not in wolves; They date back about 7,000 years and have been related, of course, to agriculture.”
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