Humanity is so genetically diverse thanks to deadly malaria, which for millennia divided Africa into isolated regions

For a long time, the scientific community held the view of a single "Garden of Eden" in Africa, from which Homo sapiens began its triumphant march across the world. However, this idea is now rejected: humans formed in different parts of the continent, lived in small isolated groups that only periodically met and intermingled.

As the popular science Telegram channel "cybulinka" pointed out, an international group of researchers published an article in Science Advances explaining the mechanics of this isolation. The main barrier between tribes was not mountains or deserts, but centers of malaria spread.

The main problem of paleoepidemiology is that scientists do not have samples of malaria plasmodium DNA from such ancient times. To understand what happened 70 thousand years ago, the authors of the study took an asymmetric approach. They created a complex climatic model of Africa for the period from 74 to 5 thousand years ago — that is, during the time of hunter-gatherers, even before the mass emergence of agriculture.

Павялічыць

Knowing the temperatures and humidity levels that existed in different eras, scientists calculated the habitats of the main disease vectors — mosquitoes of the genus Anopheles. Based on this, a "malaria stability index" was created — a map of the potential risk of infection in different regions of the continent. After that, the researchers overlaid the resulting "disease map" onto an independent map of archaeological sites, which showed where ancient people actually settled at the same time.

The result was as clear as possible: the maps practically did not overlap.

Ancient humans instinctively avoided malarial zones or simply physically could not survive there. Territories with a high risk of infection acted as absolute barriers. They cut off some human populations from others for millennia.

When the climate changed, the borders of malarial swamps receded, forming unique ecological corridors. Only then did different groups of people get the opportunity to meet, exchange knowledge and genes. In fact, the history of our evolutionary connections is the history of how humans fled from mosquitoes.

The study identified two crucial peaks in the spread of malaria. The first occurred during the period 60-50 thousand years ago. This time perfectly coincides with the main wave of human migration out of Africa. Scientists suggest that the first settlers who managed to break out of the continent very likely carried this parasite with them and enriched other regions.

The second powerful peak of malarial activity occurred about 13 thousand years ago. According to archaeological data, at this time, the periphery of human settlement began to increasingly intersect with dangerous zones, especially in West Africa. People began to penetrate where their path had previously been closed.

Genetics provides an explanation for this. It was at this time and in this region that a mutation began to spread among our ancestors, causing sickle cell anemia — a genetic anomaly of red blood cells which, despite its own danger, gives the carrier strong natural immunity against malaria.

For a long time, the stereotype in science was that malaria became a mass killer only after the Neolithic Revolution, when people began to clear forests for fields, live in one place, and create artificial reservoirs ideal for mosquitoes. However, new data prove that infectious diseases were a powerful evolutionary pressure long before the appearance of the first farmers. The survival and dispersal of our species were determined not only by the ability to hunt animals but also by the ability to withstand a microscopic parasite.

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