Bostwana, the first home of modern humans

• Eurasia: 'Homo sapiens' lived in the territory that is now Greece 210,000 years ago
• Anthropology: the first 'Homo sapiens' that left Africa

For a long period of time, which began 200,000 years ago, the direct ancestors of all modern human beings ( Homo sapiens sapiens ) lived and prospered on the banks of Lake Makgadikgadi, along a territory that today occupies northern Bostwana , eastern Namibia and western Zimbabwe. That first population marks the beginning of the L0 genetic lineage, with which all the inhabitants of the planet are related to sharing a common ancestor. The L0 is divided for the first time 70,000 years later, when large groups leave that first home of the species in search of new lands, beyond the Zambeze river basin.

This is explained by a team of scientists from different disciplines who have collaborated to reconstruct the first steps of modern Sapiens . His work, published on Monday in Nature , combines ethnolinguistic studies, archaeological records, climatic models and the analysis of more than 1,200 mitochondrial genomes of the current inhabitants of the region.

"The genetic differences begin at the moment they begin to migrate," said Vanessa Hayes, a professor at the Universities of Sydney (Australia) and Pretoria (South Africa) and head of research. "130,000 years ago we see a first group moving north-west, while 20,000 years later there is a second, larger division, this time heading south."

A third group will remain in the area, directly related to the current Khoisán villages. "Unlike the explorers in the northeast, emigrants from the southwest seem to have had more luck, experiencing steady population growth," says Hayes. Archaeological evidence found in the southern tip of the continent suggests that the success of that second wave was based on its adaptation to marine food .

Home but no crib

The authors emphasize that the study focuses on anatomically modern sapiens , a specific subspecies that includes current human beings and in which it is possible to draw a direct genetic line from the original population to the present , via mitochondrial DNA. "We talk about home, but not cradle," Hayes qualifies, "because the study only refers to a specific population, which we know is related to us, but is not the beginning of everything."

In this sense, Hayes recalls that there are other findings that go back further back in time, such as the remains of Jebel Irhoud in Morocco (at least 300,000 years old). "But, until we get DNA from those or other skeletons, it is difficult to speculate on what relationship there was between them. In the future, archaeologists and geneticists will have to collaborate to assemble the puzzle pieces."

An African Garden of Eden

Today, the Makgadikgadi region is marked by immense salt flats and large tracts of dry savannah, but, once, it hosted a huge body of water, with an area twice higher than Lake Victoria. 200,000 years ago, that great lake began to divide, creating a vast network of wetlands that allowed the first population of sapiens to settle and grow. 70,000 years later, new changes in the climate caused the opening of vegetation corridors that drive the first explorations, marking the beginning of the genetic, ethnic and cultural diversity of Homo sapiens .

"Our simulations suggest that a slight inclination of the Earth's axis changed the summer solar radiation in the southern hemisphere, causing changes in the rains of southern Africa," explains Professor Axel Timmermann, director of the Center for Climate Physics at the National University from Pusan ​​in South Korea. " When comparing the climatic records with the genetic ones, we see the same pattern : as the rains increased 130,000 years ago, a large corridor to the northwest opens, which coincides with that first genetic differentiation. 20,000 years later, we identified a second corridor that allowed movements population to the south. "

Mitochondrial Eve

In that African Eden, a mitochondrial Eva would have lived, a concept that scientists use in reference to the most recent common ancestor of the species, which transmitted the mitochondria from which all current descendants. "Mitochondrial DNA - which is only transmitted by the mother - acts as a time capsule that goes back to the first predecessors, accumulating changes slowly over generations," explains Dr. Eva Chan, of the Garvan Institute of Medical Research in Sydney, first author of the article and responsible for phylogenetic analyzes.

Therefore, comparing the mitochondrial genome of different individuals provides scientists with a tool for key information about their origin and how they relate to each other. In this case, the authors have reconstructed 198 new mitogenomas and collected data from 1,000 existing ones, all of them from current inhabitants of southern Africa, which is the largest study on the mitochondrial DNA of the L0 lineage. "We have gathered all the information available in the databases on the oldest known human population ," explains Chan. "That has allowed us to specify our evolutionary tree from the first branches with the greatest precision so far."

In this way, it has been possible to demonstrate the prolonged geographical and genetic isolation of these population groups south of the Zambeze River. Based on these data, the analysis of genomes and the establishment of mitogenomic schedules, frequencies and dispersions, it is possible to reconstruct the genetic lines until identifying at what times and places the great separations occurred throughout human evolution.

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