Demystifying science | Recent human evolution

Every week, our journalist answers scientific questions from readers.

There have been several, most often related to diet and infections.

A distinguished American geneticist, Alan Templeton, of Washington University in St. Louis, spontaneously enumerates a list: skin color in northern regions, the ability to digest milk as an adult, resistance to the plague and resistance to sleeping sickness in Africa.

“Evolution in humans is observed in relatively recent periods compared to its appearance,” indicates Mr. Templeton, who published the book in 2019 Human Population Genetics and Genomics on the subject. “We are talking about millennia, and sometimes even centuries in the case of infectious diseases. »

Tens of thousands of years ago, when humans migrated out of Africa and into the northern latitudes of Asia and Europe, they had less sunlight and therefore less vitamin D. Individuals who had lighter complexions, which make it easier to absorb vitamin D from the sun, were favored,” says Templeton.

When humans domesticated milk-producing livestock, similarly, individuals capable of digesting milk were also favored. “Normally, the ability to digest milk disappears after a few years, when the child is no longer breastfed,” illustrates the American geneticist. But some retain this ability throughout their lives. » In regions where milk consumption is historically less common, lactose intolerance is more prevalent.

Finally, deadly epidemics are one of the driving forces of evolution.

Evolution has, for example, favored genes protecting against malaria in certain Mediterranean populations, he notes. These genes, on the other hand, increase the risk of anemia.

Diabetes, famine… and questions

Mr. Templeton also cites a controversial hypothesis aimed at explaining the increased risk of diabetes in populations who have only recently adopted Western diets, for example among indigenous people of North America and the Pacific. This hypothesis suggests that certain genes making it easier to transform food into energy are found more often in these populations because of the difficulty until recently in obtaining food. She is considered racist and the famous genes have not yet been found.

“We know that among people who experienced the famine at a young age in Ukraine in the 1930s and in the Netherlands in 1945, the risk of diabetes and other metabolic diseases is higher,” explains Mr. Templeton. During famines where there is mortality, people who have a gene protecting against these metabolic diseases could be favored. But there is no epidemiological evidence of this development at the moment. »

The mechanism by which experiencing hunger at an early age predisposes to later metabolic diseases is called “epigenetic.” The expression of certain genes is modified by the environment.

But other than the survival of people who don’t have this epigenetic vulnerability, there isn’t much evidence that these epigenetic alterations are passed down from one generation to the next. “It’s thought to be possible in rats, but it’s not proven beyond doubt,” says Templeton. There is a study on genes that protect against sleeping sickness in African populations that detected epigenetic-like modifications in neighboring genes. »

The transmission of epigenetic alterations is difficult in mammals since the transmission of their genes is ensured by specialized cells, eggs and spermatozoa. If epigenetic alterations do not affect these reproductive cells, they will not be transmitted.

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