Strong monsoons may have carved a path for early humans out of Africa

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https://www.science.org/content/article/strong-monsoons-may-have-carved-path-early-humans-out-africa

By BRIDGET ALEX, Science. 

Excerpt: More than 140,000 years ago, East Asia was a much colder, drier place than today—a landscape that likely deterred many African creatures, humans among them, from venturing into the region. Then, some 100,000 years ago, roving members of our species may have reached East Asia and found a rain-soaked, verdant landscape. What changed? According to a new study published today in the Proceedings of the National Academy of Sciences, a strengthening monsoon—and the lushness it lent—helped attract the region’s first Homo sapiens. ...Evidence from fossils, artifacts, and DNA has established that H. sapiens evolved in Africa by roughly 300,000 years ago. About 60,000 years ago, the lineage that led to people alive today began to disperse across all of Earth’s habitable lands. ...One climatic phenomenon that would have impacted early migrants is the Asian monsoon. Today, this seasonal shift in winds dumps torrential summer rain that nourishes forests and farms across Asia. In winter, Siberian winds bring dry, cold conditions. Paleoclimate records ...indicate the monsoon’s intensity has waxed and waned over the millennia, but .... How wet Asia gets, the researchers learned, varies with multiple factors, including greenhouse gas concentrations, the amount of ice covering the Northern Hemisphere, and the intensity of sunlight reaching Earth, ultimately governed by the planet’s tilt, wobble, and solar orbit. Between 125,000 and 70,000 years ago, ...East Asia had spells of 27.5°C summers with more rain than the present day—an enticing environment for mammals and the hunter-gatherers tracking them. ...Meanwhile, over the same time span, climate in southeastern Africa worsened, the authors found, perhaps pushing humans to find new homelands. 

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