Record-breaking simulation shows how climate affects human migration

Massive simulations of Earth’s climate over the past 2 million years provide evidence that temperature and other planetary conditions influenced early human migration – and may have contributed to the emergence of the modern human species around 300,000 years ago.

The discovery is one of several models that have emerged from the largest model to date investigating how changes in Earth’s motion affect climate and human evolution, published in temper tantrums¹ today. “This is another brick in the wall to support the role of climate in shaping human origins,” said Peter de Menocal, director of the Woods Hole Oceanographic Institute in Falmouth, Massachusetts.

The idea that climate may have played an important role in human evolution has been around since at least the 1920s², as scientists began debating whether dry conditions prompted early human ancestors to start walking on two legs, adapting to life on the savanna. But so far, researchers have struggled to provide solid evidence that climate played a role in shaping humankind.

orbital effect

In the new study, Axel Timmermann, a climate physicist at Pusan ​​National University in South Korea, and colleagues ran climate models on a supercomputer for six months to reconstruct how temperature and precipitation might have shaped the resources available to humans in the past. Several million years. In particular, the researchers studied how long-term fluctuations in climate caused by the Earth’s astronomical movements may have created the conditions to stimulate human evolution.

The push and pull of other planets alters Earth’s climate by changing the tilt of the planets and the shape of their orbits. Over 41,000 years, the Earth’s tilt oscillates, affecting the intensity of the seasons and changing the amount of rain that falls in the tropics. And over the course of more than 100,000 years, Earth transitioned from a more circular orbit — one that brings more sunlight and a longer summer — to a more elliptical orbit, which reduces sunlight and can lead to periods of glacier formation.

Timmerman and his colleagues used simulations that combined these astronomical changes, then combined the results with thousands of fossils and other archaeological evidence to figure out where and when six hominid species — including the earliest — were discovered. Standing man and modern sane people – He can live.

Movement and blending

The study yielded an astonishing amount of data, and Timmerman said some interesting patterns emerged. For example, the researcher’s analysis shows that the early human species, Homo heidelbergensis, began expanding its habitat about 700,000 years ago. Some experts believe that this species may have given rise to a large number of other species around the world, including Neanderthals (neanderthal) in Eurasia and H. waras Somewhere in Africa.

The model shows that the distribution of H. heidelbergensis That’s possible worldwide because more elliptical orbits create wetter climatic conditions that allow species to migrate on a larger scale. The simulations also show that the most habitable areas, in terms of climate, have changed over time, and the fossil record has traced them back.

“The global collection of skulls and tools is not randomly distributed in time,” Timmerman said. It “follows a pattern” that overlaps with Earth’s motion-driven climate change. “That’s incredible to me – it’s a pattern that no one has seen until now.”

Any part of this pattern could provide new insights into where and how our species emerged. Several genetic studies of modern hunter-gatherer groups in sub-Saharan Africa – which tend to be genetically isolated – show that H. waras It is the result of a single evolutionary event in South Africa. But other studies tell a more complex story, as humanity began as a hotspot for many different groups from ancient Africa who together evolved into modern humans.

Timmerman and colleagues say their climate reconstruction supports the hypothesis of individual evolutionary pathways. The model shows that our species evolved when H. heidelbergensis In South Africa it began to lose its habitable habitat during unusually warm periods. This population can evolve into H. waras By adapting to hotter and drier conditions.

But this result is unlikely to end the controversy. “Proving that certain climatic events cause speciation events is very difficult,” said Tyler Feith, a paleobiologist at the University of Utah in Salt Lake City, in part because there are gaps in the fossil and genetic records.

The same is true for many of the other patterns mentioned in the paper. “People who have spent their careers studying this will either agree with violence or disagree with the proposals here,” de Menocal said. The model, however, is “an amazing achievement in itself” and “gives you a model for asking these questions”.

Most of the researchers who spoke to temper tantrums We say that more evidence will be needed to prove that astrological cycles influenced the course of human origins. “If the solution to the riddle of climate change and human evolution could be tackled in one paper, it would have been 40 years ago,” Feith said.

That’s why Timmerman and his colleagues plan to run larger models, including those that integrate genetic data.

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