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The encounter between Neanderthals and modern man as told by their genomes

By analyzing genomes up to 40,000 years old, a team from the University of Geneva traced the history of migration between modern humans and Neanderthals

Reconstruction of a Neanderthal family in the Neanderthal Museum in Croatia. Illustration:
Reconstruction of a Neanderthal family in the Neanderthal Museum in Croatia. Illustration:

About 40,000 years ago, the Neanderthals, who lived for hundreds of thousands of years in the western part of the Eurasian continent, retreated in favor of modern man, who came from Africa. This exchange was not sudden, and the two species coexisted for thousands of years, leading to the incorporation of Neanderthal DNA into the modern human genome. Researchers from the University of Geneva analyzed the distribution of the part of DNA that was transferred from Neanderthals to the genomes of humans in the last 40,000 years. These statistical analyzes revealed subtle changes in time and geographical space. This work, published in the journal Science Advances, helps us understand the shared history of these two species.

Thanks to genome sequencing and comparative analysis, it is known that Neanderthals and modern humans interbred with each other and that these encounters were sometimes fertile, leading to the presence of about 2% Neanderthal DNA in Eurasians today. However, this percentage varies slightly between different regions of Eurasia, as DNA of Neanderthal origin is slightly more common in the genomes of Asian populations than in Europeans.

One hypothesis to explain this difference is that natural selection did not equally affect genes of Neanderthal origin in Asian and European populations. The team of Matthias Korat, a senior lecturer in the Department of Genetics and Evolution at the Faculty of Sciences of the University of Geneva, is working on a different hypothesis. His previous work, based on computer simulations, indicates that such differences can be explained by migration flows: when an immigrant population breeds with a local population, in their shared living area, the DNA fraction of the local population tends to increase with distance from the point of origin of the immigrant population .

Europe: an area shared between the two sexes

The spread of Homo sapiens from Africa. Illustration:
The spread of Homo sapiens from Africa. Illustration:

In the case of modern man and the Neanderthals, the hypothesis is that the farther you get from Africa, the point of origin of modern man, the greater the proportion of DNA that comes from the Neanderthals, a population that lived mainly in Europe. To test this hypothesis, the authors used a database provided by Harvard Medical School, which includes more than 4,000 genomes of people who have lived in Eurasia for the past 40,000 years.

"Our research focuses mainly on European populations because we clearly depend on the discovery of bones and the state of preservation of the DNA. It turned out that there were more archaeological excavations in Europe, which greatly facilitates the study of the genomes of European populations", explains Claudio Kilodran, Senior Research and Teaching Assistant in the Department of Genetics and Evolution at the Faculty of Sciences of the University of Geneva, and first partner in the study.

Statistical analyzes revealed that in the period following the spread of modern humans from Africa, the genomes of Paleolithic hunter-gatherers living in Europe contained a slightly larger proportion of Neanderthal DNA than the genomes of those living in Asia. This result is contrary to the current situation, but it is consistent with paleontological data, since the presence of Neanderthals was reported mainly in Western Eurasia (Neanderthal bones were not discovered east of the Altai region in Siberia).

The arrival of farmers from Anatolia changes genomes

Later, during the transition to the Neolithic period, that is, the transition from a lifestyle of gathering and hunting to agriculture, 10,000 to 5,000 years ago, the study shows a decrease in the proportion of DNA of Neanderthal origin in the genomes of European populations, which led to a slightly lower percentage than that of Asian populations (as observed today ). This decline coincided with the arrival in Europe of the first farmers from Anatolia (the large peninsula in the Asian part of Turkey) and the Aegean Sea region, who themselves carried less DNA of Neanderthal origin than European residents at the time. By mixing with European populations, the genomes of the farmers from Anatolia "diluted" the Neanderthal DNA slightly.

This study shows that the analysis of ancient genomes, in combination with archaeological data, makes it possible to trace different stages in the history of interbreeding species. "In addition, we are beginning to have enough data to describe with increasing precision the percentage of DNA of Neanderthal origin in the modern human genome during certain periods of prehistory. Therefore, our work can be used as a reference point for future studies to more easily identify genetic profiles that deviate from the average and therefore may reveal a beneficial or harmful effect", concludes Matthias Kurat, the last author of the study.

For the scientific article in Science Advances

More of the topic in Hayadan:

2 תגובות

  1. A primary test for an animal species is the joint procreation of fertile individuals. A dog and a wolf, despite the obvious differences between them, give birth to fertile offspring together, so they are actually one species. A horse and a donkey give birth to infertile offspring, so they are different species. Homo sapiens and Neanderthals produced fertile offspring together, so they were one species, despite their considerable differences. In the future, researchers who discover remains of people from Africa and the Andes and Europe, may speculate that these were distinct species.

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