He superpower which allows us humans to start transforming the starch in foods with our saliva, was created much earlier than expected, according to work published this Thursday in the journal Science.
Research carried out by Omer Gokcumen, of the University at Buffalo (UB), locates the origin of this revolution metabolism more than 800,000 years ago, when duplication of the salivary amylase gene (AMY1), which facilitates this capacity, 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 must 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 the starch in the stomach. mouth. This explains why if we leave a piece of bread on our tongue, we notice a sweet taste, a capacity which scientists place the origin of at the beginning of agriculture, around 10,000 years ago, and which is also present in our pets, exposed to the same starchy diets as us.
Raised over low heat
The new work was based on genome analysis of 68 ancient human remains, including a 45,000-year-old sample from Siberia. The authors found that pre-agricultural hunter-gatherers already owned on average four to eight copies of AMY1suggesting that humans were already roaming Eurasia with large numbers of copies of this gene, long before they began domesticating plants and eating excessive amounts of starch.
The study also indicates that gene duplications occurred AMY1 among Neanderthals and Denisovans, leading them to conclude that this key change occurred long before our species split from Neanderthals and give the figure of at least 800,000 years ago. “The initial duplications of 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 new technologies and new 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 could be linked to 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 later proved fundamental to our species. As humans have developed in different environments, gene copy number flexibility has 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 place The amylase became unstable and started generating new variations,” explains Charikleia Karageorgiou, one of the lead authors of the study. From three copies of AMY1you can get up to nine copies. So when the Neolithic Revolution arrived, change was already underway.
The new research also documents how agriculture has affected the variation in AMY1 in European farmers, who saw an increase in the average copy number of the gene over the past 4,000 years, likely due to their starchy diet. A result that is consistent with Gokcumen’s previous research, in which he showed that domestic animals such as dogs and pigs also have higher numbers of copies of AMY1 compared to animals that do not rely on a starchy diet.
It is likely that individuals with higher numbers of copies of “AMY1” digest starch more efficiently and have 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 copy number by AMY1 digest starch more efficiently and have more offspring,” says Gokcumen. “Ultimately, their lineages performed better over a long period of evolution than those with lower copy numbers, which spread the copy numbers of AMY1.
Why do we eat potatoes and cereals?Yes
For Gemma Marfany, professor of genetics at the University of Barcelona (UB), the genomic analysis is very well developed at the methodological level, given that the genomic region that contains the amylase genes, being duplicated and with sequences very homologous, is not easy to align and analyze. “The presence of this amylase gene, necessary to break down starch, has helped us digest and benefit from plants rich in carbohydrates that provide us with energy, such as potatoes and other tubers, rice, wheat and other cereals,” he points out, “expressing more amylase in saliva gave our ancestors an advantage over a single copy of the gene.” AMY1as did chimpanzees and gorillas and, later, with the advent of agriculture and the domestication of cereals, this pressure of natural selection increased further.
“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 strongest signs of positive selection in our DNA,” explains Antonio Salas, geneticist at the University of Santiago (USC). According to him, this work represents a considerable technical challenge, in addition to the effort of bioinformatics and evolutionary analysis 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 by which gene copy number variability confers an adaptive advantage , particularly in different cultural contexts with significant dietary variability,” he emphasizes.
“What the authors deduce from their study is that the first duplications could have occurred before the divergence of modern humans, Neanderthals and Denisovans,” explains Spanish paleoanthropologist and academic José María Bermúdez de Castro. “This divergence has been estimated between 550,000 and 765,000 years ago, although some authors put it back to 800,000 years ago, and this is the date used by the authors of the work.” Since there is evidence of the use of fire for cooking at one site in Israel (Daughters of Jacob Bridge), dated around 780,000 years ago, the authors consider that the use of fire for cooking – which allows food to be better digested – could have influenced the duplication of the gene AMY1he emphasizes.
The ability to ingest starch from cooked tubers thanks to these duplications could also be linked to an increase in cranial capacity.
Carles Lalueza-Fox
— Ancient DNA specialist
These findings suggest a fascinating possibility, namely that learning to use fire may have led to a change in our saliva and opened the door through which the agricultural revolution that followed eventually took place. “This is an interesting hypothesis, because the ability to ingest starch from cooked tubers thanks to these duplications could also be linked to an increase in cranial capacity,” adds the former DNA specialist. Carles Lalueza-Fox. Although there has been other previous work on this gene that proposed duplications after modern humans and Neanderthals split, remember, the most relevant is that here they find some variability in archaic genomes and suggest an earlier date. “And there is a nice parallel story,” he points out, “which is that duplications of this gene are also found in dogs and not in wolves; They date back about 7,000 years and are of course linked to agriculture.
