origin of humans; migration to Asia controlled by climate (Origins)

by David Turell , Tuesday, January 09, 2024, 16:07 (110 days ago) @ David Turell

About 100,000 years ago as climate changed:

https://mail.google.com/mail/u/0/#inbox/FMfcgzGwJchvfjLhvTTCjpkhmdChWdGc

"Our species evolved in Africa some 300,000 years ago, but fossil evidence suggests people didn't begin migrating into East Asia until around 100,000 years ago. What took them so long? A new analysis of ancient climate conditions suggests these eastbound migrants had to wait until a strengthening monsoon pattern across southern Asia rolled out a green carpet for them.

"Before about 125,000 years ago, people journeying east out of the African continent would have encountered cold, arid conditions inhospitable to modern humans. But then, a lot changed—including greenhouse gas concentrations, the volume of ice covering the Northern Hemisphere, and the intensity of sunlight reaching Earth, ultimately governed by the planet’s tilt, wobble, and solar orbit. Combined, these increased heat and rainfall across the region, and this new climate produced a green corridor, the authors argue, that would have proven irresistible to hunter-gatherers at the time, drawing them into East Asia.

“'Now we can confidently add rain and water to the equation that makes environment more suitable for H. sapiens settlement,” says anthropologist and study author María Martinón-Torres."

From the original article:

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

"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. But remains that resemble H. sapiens, reportedly dated to between 120,000 and 70,000 years old, have surfaced at various East Asian sites, including Fuyan Cave in China and Tam Pà Ling in Laos. Those putative modern human groups may not have persisted, and anthropologists debate what drove them to venture out in the first place.

***

"A team led by Chinese Academy of Sciences geologist Hong Ao sought a record that could track the timing of these changes on a scale of centuries. In 2021, they found what they were looking for: a slope of the Chinese Loess Plateau where windblown sediment had accumulated relatively quickly, creating a high-resolution record. For 1 month, the researchers dug steps into the plateau and shoveled sediments about every 2 centimeters along a 44-meter slope. From 2066 samples, they measured magnetic particles that form more abundantly as wetter conditions hasten the formation of soils with iron minerals. This provided snapshots of monsoon intensity every 100 to 800 years for the past 280,000 years.

"The researchers combined this record with a climate simulation model and existing environmental reconstructions to make estimates for annual rainfall, summer temperature, and other climate variables.

***

"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, when H. sapiens likely apparently first ventured there, 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.

“'Now we can confidently add rain and water to the equation that makes environment more suitable for H. sapiens settlement,” says study author María Martinón-Torres, an anthropologist with Spain’s National Research Center on Human Evolution."

Comment: H. erectus was certainly prone to migration, always looking for the best spots to live. This theory does not explain the thinking that North America was colonized across an ice bridge to Alaska. Not a hospitable climate in that instance.