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Human evolution appears written on the ground

The earth cylinder, cut into sections, has made it possible to reconstruct a million years of environmental changes.Human Origins Program, Smithsonian

Until the current climate crisis, the different environmental changes have been marking the future of human evolution. Various studies support the connection of climate with the progress of some hominin species and the retreat of others, such as the Neanderthals in Europe. But like almost everything in human history, this story began in Africa. The analysis of a cylinder of earth of tens of meters has allowed to see how the alteration of the environmental conditions spurred the human advance.

For hundreds of thousands of years, the first humans of the Great Rift Valley, a geological fracture that crosses the eastern African continent, lived in an environment with little change. The rainfall regime allowed to maintain a large population of herbivores and safe sources of water with which to sustain those human communities. But then everything changed. The climate became unstable, extreme and more arid. And humans had to adapt or die.

This is what a team of researchers from the Smithsonian Institution’s Museum of Natural History (USA) has verified. As has been done in the polar caps, they drilled the earth to extract a cylinder with the successive layers of sediment from the last million years. From their study they have been able to infer what the climate was like and how it was changing. They then collated their climatic record with different archaeological remains from the Olorgesailie site, in present-day Kenya, to intuit the connection between climate and changes in hominin technology and way of life.

As told in the scientific journal Science Advances, the humans of this region used the same stone tools for about 700,000 years. His way of life during all this time was very stable. But about 320,000 years ago they entered a new phase of history, a Middle Stone Age, where tools were less crude, smaller, with sharper weapons, and built for use as projectiles. In addition, they are the times in which they begin to use different pigments for coloring, which suggests the development of symbolic communication. They also expanded their movements on the ground in a kind of proto-trade. All coinciding with a prolonged period of environmental instability.

“The history of human evolution has been characterized by increasing adaptability,” says study lead author Richard Potts, director of the program, in a note from the Smithsonian Institution. Human origins of this institution. “We come from a family tree that is diverse, but all other forms of human being have become extinct. Only we are left and we could well be the species with the greatest capacity for adaptation that has ever existed on Earth ”, he adds.

To confirm the climate connection of cultural change, the researchers drilled the ground 15 miles from the Olorgesailie site. They extracted a 139 meter cylinder (cut into sections) and four centimeters in diameter. Then they studied its chemical composition, the presence of different carbon isotopes or sedimented organic remains to estimate what the landscape was like and why it changed.

The land shows that, several thousand years before humans in the region began to do things differently, the availability of water was complicated, probably by the combination of tectonic activity and the alteration of the rainfall regime. This must have changed the entire ecosystem.

“There was a huge change in fauna during the time period that we see behavior change in these early humans,” says Potts. “Animals also affected the landscape through the plants they ate. So humans, with some of their innovations, such as throwing weapons, must also have affected wildlife. It was the entire ecosystem that changed, with humans inside ”, he concludes.