2. Recent adaptations: elevation, fat, infections

“As humans migrated, they found themselves in different environments and had to adapt,” explained Emilia Huerta-Sánchez, professor at the University of California, Merced, in the United States. One of the adaptations can be seen in the inhabitants of Tibet, used to living at high elevations where the air has considerably less oxygen than at sea level.

When other populations climb to higher elevations, their bodies react by producing more hemoglobin and red blood cells. This helps the blood transport more oxygen and compensate for the fact that there is less available (this is what many athletes look for when training at high elevations). This strategy, however, comes with its risks: the more cells in the blood, the thicker it is and the greater the risk of clots.

Tibetans, however, don’t have high hemoglobin levels. Why don’t their bodies react in the same way? The answer seems to be in the EPAS1 gene, among others. Scientists believe a mutation of the gene, widespread among this population, changes this response and protects them against thickening blood. “This adaptation seems to have come from introgression of the Denisovans,” Huerta-Sánchez explained and published (it has hardly ever been found beyond the Tibetan and Denisovan populations). “And it seems to have continued being selected for the past 3,000 years,” added Anna di Rienzo, professor at the University of Chicago. What isn’t totally clear are the genetic traits that allow them to work at high elevations. Some could be associated with the EPAS1 gene, which has many functions. These seem to include ones that help increase the number of blood vessels (capillaries) in muscles.

Another example of a recent adaptation can be seen in the Inuit population, the native inhabitants of Greenland. Given their environment, for many years they have eaten “a diet low in carbohydrates and very high in proteins and omega-3 fatty acids (found in fish and marine mammals),” said Rasmus Nielsen, professor at the University of California, Berkeley. The “consequences” can be seen in their genome: a selection has occurred in the genes responsible for synthesizing fatty acids. Their bodies produce fewer of their own to compensate for the huge amounts they consume. This is why “we can’t directly extrapolate the theoretical benefits of their diet to other populations.”

There are more examples that consistently demonstrate recent adaptations: in areas where malaria is endemic, most of the population bears a mutation of the hemoglobin gene that causes sickle-cell anemia. The risk is compensated because this variant protects against infection.

Bertranpetit’s group showed that pygmies on the Andaman Islands, in the Indian Ocean, had been selected to be shorter, which when there are no predators has certain metabolic advantages. And his team also participated in describing how the plague helped select the genomes of many Europeans, those most resistant to the infection.

If there is one thing subject to evolution, it seems to be our defenses.