One ancestor or numerous crossings: where did the reasonable man come from

The most common evolutionary theory suggests that Homo sapiens evolved from

the only local population of the previous speciesgenus Homo in Africa between 300,000 and 100,000 years ago. Our ancestors actively spread across the continent and beyond and gradually displaced or assimilated other species.

Archaeological and paleogenetic datais not enough to unambiguously confirm or refute this hypothesis and describe the early migration of people across the African continent. In a study published in the journal Nature, an international team of biologists and geneticists uses genetic analysis of modern Africans and their ancient ancestors, as well as statistical modeling, to unravel the origin of Homo sapiens.

The traditional view of the evolution of Homo sapiens

The dominant scientific theory suggests that allthe global population of Homo sapiens descended from one local population located in Africa. From this source, further development is a tree structure.

This model has become popular because itcorresponds to the general principle of biological evolution, in which geographically dispersed groups of the same species are largely genetically isolated, and there is practically no interbreeding between individuals belonging to different populations.

As a result of the lack of cross flowgenes there is a gradual drift of genes - the accumulation of random mutations that differ in different populations of the same species. Under the pressure of natural selection over time, genetic differences increase to such an extent that members of these different populations become genetically incompatible and can no longer produce viable offspring. Separate species are formed.

The disadvantage of this theory, as the authors believeof the new study is that it does not agree well with the archaeological and fossil evidence. Artifacts found in different regions of Africa indicate a relatively synchronous (on a geological time scale) emergence of various primitive technologies among disparate groups of people.

In addition, the fact that in the DNA of modern humansfrom 1 to 2% is the Neanderthal genome, suggests that representatives of different "species" have retained the ability to interbreed - the genetic divergence has not reached the limit after which the birth of healthy offspring is impossible.

What did scientists study?

To determine the origin of Homo sapiens inIn the absence of sufficient ancient DNA to analyze, the researchers focused on modern Africans. From a large study of the genetic diversity of Africans, they selected data from 290 individuals from four geographically and genetically distinct African groups to trace similarities and differences between populations over the past million years and gain insight into genetic relationships and human evolution across the continent.

The study included representatives of the peoplesNama (inhabitants of South Africa); Mende (from Sierra Leone); the Humuzes (recent descendants of a group of hunter-gatherers from Ethiopia); and the Amhara and Oromo (agricultural people from East Africa). To assess the possible impact of “reverse gene transfer” from Europe, the researchers further analyzed data from the British Biobank.

Different models of development of different populations of Homo sapiens used for modeling. Image: Aaron P. Ragsdale et al., Nature

The researchers used an algorithm thatmodeled possible scenarios for the spread of genes (crossing between representatives of different populations) over the past hundreds of thousands of years. The analysis showed that modern genetic diversity is best provided by models that assume numerous gene transfers between different remote peoples.

We wrote this algorithm to understand how the riskGenetic diseases vary across populations, and this has led us to a deep understanding of human origins. It was very interesting to link applied and fundamental research in this way.

Simon Gravel, study co-author at McGill University

What conclusions did geneticists come to?

The researchers found that the best modelHuman evolution in Africa includes several populations that interbred and migrated over time. At least two evolutionary branches of Homo sapiens split between 120,000 and 135,000 years ago, but continued to mix.

Geneticists believe that this "weaklystructured trunk" (consisting of a mixture of these two branches) contributed to the formation of the ancestral African human group, which then branched into modern African populations, as well as populations living outside Africa.

The two models that best describe current genetic diversity in Africa. Image: Aaron P. Ragsdale et al., Nature

The researchers also found that archaichominids did not contribute to the evolution of modern man. This means that morphologically distinct hominin fossils, such as Homo naledi, are unlikely to represent branches that contributed to the evolution of Homo sapiens.

The results of the study provide a new perspective onhuman evolution, scientists say. The principles of evolution are essential to the interpretation of the fossil record. In addition, they will help to better understand the diversity of populations and the genetic basis of the various traits of people.

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On the cover: Image by brgfx on Freepik