Over time, our diet dramatically changes our anatomy, our immune system, and maybe skin color.
in fact, we are not what we eat. However, what we eat influences the path of our evolutionary development for many generations. Diet, says anthropologist John Hawks of the University of Wisconsin in Madison, is a very important element in our evolutionary history. We believe that over the past million years, some changes in human anatomy, teeth and skull are related to changes in diet.”
Our evolution continues, and diet remains essential. Genetic studies show that humans are still evolving, and the effects of natural selection on genes affect literally everything from Alzheimer's and skin color to the age of menstruation. And what we eat today will influence the direction of our movement tomorrow.
Do you have milk?
When mammals are young, they produce the enzyme lactase, which helps digest the sugar lactose found in breast milk. But as mammals mature, milk disappears from their diet. This means that the lactose-digesting enzyme is no longer needed, and therefore adult mammals usually stop producing it.
But thanks to evolution, some people disprove this trend.
About two thirds of adults are lactose intolerant or have reduced tolerance. However, portability varies greatly depending on geography. In some parts of East Asia, lactose intolerance can be as high as 90 percent. In particular, lactose is poorly tolerated by residents of West African countries, Arabs, Greeks, Jews and Italians.
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On the other hand, northern Europeans seem to be in love with lactose, because 95 percent tolerates it there. That is, even in adulthood, they continue to produce the enzyme lactase. "In at least five regions, the population has adjusted their gene for digesting this carbohydrate, and it remains active in adults," says Hawkes, noting that it is most common among peoples in Europe, the Middle East and East Africa.
Ancient DNA shows that lactose tolerance in adults is a recent evolutionary measure. She was absent 20 thousand years ago. Today, lactose is tolerated by about a third of all adults.
This rapid evolutionary change suggests that milk consumption was likely to provide significant survival benefits over those who had to ferment it into yogurt or cheese. During fermentation, bacteria break down milk sugar, including lactase, converting it into acids and making it easier for those who are lactose intolerant to digest. But along with these sugars, a large proportion of food calories goes away.
Hawkes explains why the ability to digest milk has been so valuable in the past: “People have been limited in their food, but if you have cows, sheep, goats or camels, you have the opportunity to eat high-calorie foods that children digest but adults do not. This allows a person to extract 30 percent more calories from milk, and he does not have the digestive problems that occur when consuming milk."
A recent genetic study showed that lactose tolerance in adults was less prevalent in Roman Britain than it is today. This means that evolution also continued throughout the chronicle history of Europe.
Many people now have access to a variety of alternative foods, as well as lactose-free milk and lactase tablets, which help them digest dairy products. In other words, we can get around some of the consequences of natural selection. This means that some individual traits, such as lactose tolerance, may not have the same direct impact on survival and reproduction as in the past, at least in some regions of the world.
“As far as we know, in Sweden, the ability or inability to digest milk does not make any difference to the survival and reproduction of offspring. If you eat food from the supermarket, your tolerance to dairy products does not affect your lifespan in any way. But in East Africa it still matters,”says Hawkes.
Wheat, starch and alcohol
Today, you can often find whole shelves of gluten-free (gluten-free) foods in stores. These are cookies, crackers and bread. But the difficulty in digesting gluten, which is the main protein in wheat, is another relatively recent challenge in human evolution. People began to store and regularly eat grain only about 20 thousand years ago, and they took up the cultivation of wheat seriously only 10 thousand years ago.
But when wheat and rye became an integral part of the human diet, celiac disease, or celiac disease, became widespread. “You look at it, and you wonder: how could this have happened?” Says Hawkes. "Natural selection shouldn't have produced that result."
The answer lies in the response of the immune system. The gene system, known as the human major histocompatibility complex, is involved in the fight against disease and often creates new variations so that a person can resist ever-changing infections. Unfortunately, in those people who have celiac disease, this system mistakes the human digestive system as a disease and attacks the intestinal mucosa.
But despite the obvious dangers of celiac disease, evolution does not appear to be reducing the incidence of disease. The gene variants behind the disease are as prevalent today as they were when people began to eat wheat.
“This is where selection to help fight disease and parasites has the side effect of causing celiac disease in a small number of people. This is the legacy that evolution has left us. It was not an adaptation to the diet, but an adaptation against the diet,”says Hawks. Unintended consequences are not uncommon in the evolutionary process. For example, genetic mutations in red blood cells that help a person fight malaria also lead to a deadly disease called sickle cell disease.
Other examples of ongoing evolution due to changes in diet are also quite curious, but here the situation is more uncertain. For example, there is an enzyme called amylase, which helps saliva to digest starch. Historically, the agricultural peoples of western Eurasia and Central America have more copies of the corresponding gene. Is this a result of selection so that they can better digest starch? “This is a very interesting story, and perhaps it is. But biology is a complex science, and now we are not completely clear what mechanism is operating here, and how important it is,”says Hawkes.
A third of East Asians (Japanese, Chinese, Koreans) have a reddening reaction when they absorb alcohol, because during their metabolism, they produce an excess of the toxic enzyme acetaldehyde. There is strong genetic evidence that such a reaction has appeared recently, over the past 20,000 years, says Hawkes.
Its appearance in the genome roughly coincides with the beginning of the cultivation of rice 10,000 years ago, and some scientists believe that it prevented people from consuming excessive amounts of rice wine. But the time frame is not quite precisely defined, both for the mutation and for the cultivation of rice. It is also believed that acetaldehyde protects against parasites that cannot tolerate this toxin.
“To a certain extent, it mattered a lot to people in the past, because it didn't happen very often then and now it is widespread,” says Hawkes. "This is a major change, but in fact, we don't know why it happened."
More important than we think?
Even a person's skin color can change (at least in part) in response to changes in diet (there are other factors, including sexual selection). Today's variety of skin colors in humanity is a relatively new phenomenon. The standard hypothesis is that there is more ultraviolet rays at equatorial latitudes. Our body needs vitamin D, and therefore our skin produces it under the influence of ultraviolet radiation. But excessive amounts of ultraviolet rays cause harmful effects, and darker skin pigments are more successful at blocking them.
According to this hypothesis, when a person began to move to less sunny and colder latitudes, his skin no longer needed protection from powerful ultraviolet radiation, and it brightened in order to produce more useful vitamin D with less sunlight.
But comparative studies of the DNA of modern Ukrainians and their prehistoric ancestors indicate that the skin color of Europeans has been changing for the last 5,000 years. This is explained by another theory, which is that skin pigmentation could occur under the influence of diet. So, if the early farmers suffered from a lack of vitamin D, then their ancestors from among the hunters and gatherers received it in sufficient quantities, feeding on fish and animal meat.
Nina Jablonski, a color researcher at Penn State University, told Science magazine that new scientific evidence suggests that "avoiding regular vitamin D intake as a result of the transition to a sedentary agricultural life could cause a gradual lightening of skin color." …
It's hard to see evolution in action. However, new technologies such as genome sequencing and the computational power of computers, which can process huge amounts of data, make it possible to notice the tiny genetic changes that, over many generations, cause real evolutionary shifts. Today, more and more often, genetic databases are compared with medical histories and factors such as diet, and this helps scientists to observe how they interact and relate.
Evolutionary biologist Hakhamanesh Mostafavi of Columbia University conducted one such study of the genome, analyzing the DNA of 215,000 people in an attempt to understand how humans evolve over a generation or two. “It's clear that our diets are radically changing today, and who knows what the evolutionary implications will be,” says Mostafavi. “There may not be a direct breeding effect, but interaction with genes that control traits is possible.”
Mostafavi's genetic studies have also shown that some options that shorten human life, such as the one that causes the smoker to increase their tobacco consumption in excess of the norm, still encounter active resistance in the selection process.
“We are seeing a direct impact of this gene on human life expectancy today,” he explains. - One can imagine that the diet has a similar effect. Recently, we have been experiencing numerous changes in the diet, say, with the advent of fast food, and we simply do not yet know what the consequences of this may be, and whether they will be."
Fortunately, thanks to the work of scientists like Mostafavi and Hawks, we may not need 20,000 years to figure this out.
Brian Handwerk
