Science.-Weather patterns like El Niño drove human evolution

06-01-2021 The Ngorongoro on the edge of the Serengeti in Tanzania is home to abundant wildlife. However, climate change leads to dramatic water shortages, changes in vegetation and loss of biodiversity that threaten the fragile ecosystem POLITICA INVESTIGACIÓN Y TECNOLOGÍA PROF. MARTIN TRAUTH, UNIVERSITY OF POTSDAM


Climatic patterns such as El Niño were the main drivers of environmental change in sub-Saharan Africa in the last 620,000 years, the time frame for the evolution of our species.

This allowed the group to reevaluate the existing climate framework of human evolution, a scientific consortium led by Dr. Stefanie Kaboth-Bahr of the University of Potsdam has found.

The group found that these ancient weather patterns had more profound impacts in sub-Saharan Africa than the glacial-interglacial cycles most commonly related to human evolution, as published in the journal Proceedings of the National Academy of Sciences.

Although it is widely accepted that climate change drove the evolution of our species in Africa, the exact nature of that climate change and its repercussions are not well understood. Glacial-interglacial cycles have a strong impact on climate change patterns in many parts of the world, and are supposed to also regulate environmental changes in Africa during the critical period of human evolution in the last million years. Ecosystem changes driven by these glacial cycles are believed to stimulate the evolution and dispersal of early humans.

Dr. Kaboth-Bahr and her colleagues integrated 11 climate files from across Africa spanning the past 620,000 years to generate a complete spatial picture of when and where wet or dry conditions prevailed on the continent.

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“We were surprised to find a marked east-west climatic ‘swing’ very similar to the pattern produced by the El Niño weather phenomenon, which today profoundly influences the distribution of rainfall in Africa,” explains Dr. Kaboth-Bahr.

The authors deduce that the effects of the tropical Pacific Ocean on the so-called ‘Walker Circulation’ – a belt of convection cells along the equator that influences rainfall and aridity in the tropics – were the main driver of this climatic fluctuation.

The data clearly show that the wet and dry regions moved between the east and west of the African continent on time scales of approximately 100,000 years, and that each of the climatic changes was accompanied by major changes in the flora and fauna of mammals.

“This alternation between dry and wet periods appears to have governed the dispersal and evolution of vegetation and mammals in East and West Africa,” explains Dr. Kaboth-Bahr. “The resulting environmental mosaic was probably a critical component. of human evolution and early demographics as well. “

The scientists note that while climate change was certainly not the only factor driving early human evolution, the new study nevertheless offers a novel perspective on the close link between environmental fluctuations and the origin of our earliest ancestors.

“We see many species of pan-African mammals whose distributions coincide with the patterns we identified, and whose evolutionary history seems to articulate with the oscillations of humidity and dryness between East and West Africa,” adds Dr. Eleanor Scerri, one of the co-authors and evolutionary archaeologist at the Max Planck Institute for the Science of Human History in Germany.

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“These animals retain cues from the environments in which humans evolved, and it seems likely that our human ancestors may have been similarly subdivided across Africa under the same environmental pressures,” he adds.

The scientists’ work suggests that an alternating seesaw pattern of rainfall between East and West Africa likely had the effect of creating critically important ecotonal regions – the transition zones between different ecological zones, such as grasslands. and forests.

“Ecotones provided diverse, resource-rich and stable environmental environments that are believed to have been important to early modern humans,” adds Dr. Kaboth-Bahr. “They certainly appear to have been important to other faunal communities.”

For scientists, this suggests that the interior regions of Africa may have been critically important in fostering long-term population continuity.

“We see archaeological signatures of early members of our species throughout Africa,” says Dr. Scerri, “but innovations come and go and are often reinvented, suggesting that our deep population history saw a constant pattern of growth and development. local population collapse in the shape of a sawtooth. Ecotonal regions may have provided areas for long-term population continuity, ensuring that the larger human population carried on, even if local populations often became extinct. ” concludes.

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