Migrations and interbreeding between Homo sapiens and Neanderthals reconstructed in a genetic study

Homo sapiens and Neanderthal skulls
An article published in the journal “Science Advances” reports the results of a genetic analysis that reconstructs the interbreeding between Homo sapiens and Neanderthals (Photo of the skulls belonging to the two species: courtesy¬†Claudio Quilodr√°n. All rights reserved) that occurred during the migrations of populations of these two species. A team of researchers from the University of Geneva, Switzerland, analyzed the DNA of over 4,000 Homo sapiens who lived in Eurasia over the last 40,000 years. The results show variations in the presence of genes inherited from Neanderthals following various interbreedings in different populations and at different times.

Advances in genetic analysis made it possible to obtain at least partial DNA from several Neanderthal individuals, and the information obtained showed which genetic characteristics were specific to Neanderthals. The discovery that Neanderthal genes are common in Homo sapiens at an average rate of around 2% indicates that the two species interbred when Homo sapiens migrated from Africa to Europe.

Differences in the percentage of Neanderthal genes present in different Homo sapiens populations have been noted, and groups of scientists are trying to explain the reasons for those differences. One hypothesis is that natural selection had different effects on populations of different areas of Eurasia. However, according to researchers from the University of Geneva, these differences are due to migratory flows that led to interbreeding between the two species at various times and in various places.

The researchers used a Harvard Medical School database that contains more than 4,000 genomes from individuals who lived in Eurasia over the past 40,000 years. These are mainly Europeans because discoveries of bones in such a state of preservation that allowed the recovery of the genome occurred mainly in Europe.

A statistical analysis indicates that, in the period following the migration of Homo sapiens from Africa, hunter-gatherers living in Europe had slightly more DNA inherited from Neanderthals than those living in Asia. Today the situation is the opposite but the result matches our paleontological knowledge given that no traces of Neanderthals have ever been found further east than the Siberian region of the Altai Mountains.

In a later period, during the transition to the Neolithic with the transition from hunter-gatherers to farmers between 10,000 to 5,000 years ago, the genetic study shows a decline in the amount of DNA inherited from Neanderthals in European populations. That decline coincides with the arrival to Europe of the first farmers from Anatolia and the Aegean area. These are populations that had a lower quantity of DNA inherited from Neanderthals than that of Europeans of the time. In essence, those migrations “diluted” the genes inherited from Neanderthals.

These results, illustrated in detail in the study, show how it’s possible to reconstruct the traces of interbreedings between Homo sapiens and Neanderthals and of migrations by putting together sophisticated genetic analyzes and archaeological data. Previous genetic studies had already aroused interest also from a medical point of view for some influences on health brought about by genes inherited from Neanderthals.

A study recently published in the journal “iScience” indicates a link between some genes inherited from Neanderthals and the risk of falling ill with severe Covid-19. This highlights the importance of genetic studies that are not only linked to the origins of modern humanity but also to health issues that may concern past, present, and future epidemics. It’s another side of a now truly vast field of research that continues to show how the history of humanity is linked to migrations of populations that interbred when they coexisted.

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