Climate change has been shaping human existence for a long time. Researchers, who published their findings today, September 21, in the journal Nature, say our prehistoric ancestors dispersed across the globe in waves, inspired by dramatic changes in the world’s climate.

Exactly how and why our distant ancestors found their way through and out of Africa is the subject of much speculation and research. Earlier studies have concluded that Earth’s orbit caused natural and widespread climate changes in the Late Pleistocene epoch 126,000 to 11,000 years ago, and that these changes might have driven Homo sapiens to scatter and spread across the shifting continents.

To test this theory, researchers at the University of Hawaii at Manoa decided to look for clues in the planet’s climate. They created a computer simulation that tracked changes in life—sustaining elements like vegetation, glacier melt, sea level, and temperature—that could have forced humans to get up and go. 

Their results suggest that early humans did indeed spread in waves. In fact, there were distinct cycles of human exit from Africa, the most significant of which happened around 60,000 years ago, according to the data.

Study co-author Tobias Friedrich created this video depicting human dispersal and density from Africa throughout the world from 125,000 years to 1000 years ago. 

There was one unexpected finding: According to this model, around 80,000 years ago there was a small but rapid human migration into Europe. Unlike the rest of the model’s conclusions, this time estimate conflicts pretty significantly with the archaeological record, which puts the first modern people in Europe no earlier than 45,000 years ago.

William Harcourt-Smith is a paleoanthropologist at the American Museum of Natural History. He was not affiliated with the current study. “This sort of modelling, trying to think about the dispersal of modern humans across the globe in a truly biogeographical sense, is to be applauded,” he told mental_floss.

But Harcourt-Smith is not convinced by the new paper’s pushing back of the first human arrival in Europe by some 35,000 years. The evidence for the first entry occurring about 45,000 years ago is sound, he says: “We know this from the fossil record (modern humans look very different from late Pleistocene Neanderthals) and the distinct archaeological markers found only at modern human sites.”

While fascinating, he says, the new paper is “very, very speculative at best” and should be considered a jumping-off point for further research.

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