Record-breaking simulations show how climate affects human migration

Massive simulations of Earth’s climate of 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 modern human species around 300,000 years ago.

The discovery is one of several models to emerge from the largest model to date investigating how changes in Earth’s motion affect climate and human evolution, published in temper nature¹ today. “This is another brick in the wall to support the role of climate in shaping the origin of man,” says Peter de Menocal, director of the Woods Hole Oceanographic Institution in Falmouth, Massachusetts.

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

orbital effect

In the latest study, Axel Timmermann, a climate physicist at Pusan ​​National University in South Korea, and colleagues run a climate model on a supercomputer for six months to reconstruct how temperature and precipitation might have shaped resources that were available to humans in the past. A few million years ago. Specifically, the researchers studied how long-term fluctuations in climate caused by the astronomical motion of the Earth may have created the conditions to stimulate human evolution.

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

Timmerman and his colleagues used simulations that incorporated these astronomical changes, then combined their results with thousands of fossils and other archaeological evidence to work out where and when six species of hominids — including the earliest — were Homo erectus and modern sane man – He can live.

Movements and mixing

The study pumped out an astonishing amount of data, and Timmerman says several interesting patterns emerged. For example, researchers’ analysis showed that early human species, Homo heidelbergensis, began to expand its habitat about 700,000 years ago. Some scholars 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. sane Somewhere in Africa.

The model indicates that the distribution of H. heidelbergensis It was possible worldwide because the more elliptical orbit created wetter climatic conditions that allowed the species to migrate on a larger scale. The simulations also showed that the most habitable areas, in terms of climate, have changed over time, and trace the fossil record with them.

“The global collection of skulls and tools is not randomly distributed in time,” says Timmerman. It “follows a pattern” that overlaps with Earth’s motion-driven climate change. “This is amazing to me – this is a pattern that no one has been able to see until now.”

One part of this pattern may provide new insight into where and how our species came to be. Some genetic studies of modern hunter-gatherer groups in sub-Saharan Africa – who tend to be genetically isolated – suggest that H. sane 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 of ancient Africans who together evolved into modern day humans.

Timmerman and colleagues say that their climate reconstruction favors the individual evolutionary path hypothesis. The model indicates that our species evolved when H. heidelbergensis In South Africa it began to lose its livable habitat during an unusually warm period. This population can evolve into H. sane By adapting to hotter and drier conditions.

But this outcome is unlikely to end the controversy. “Proving that a particular climatic event led to a speciation event is really difficult,” says Tyler Feith, a paleobiologist at the University of Utah in Salt Lake City, in part because there are gaps in the fossil and genetic record.

The same goes for many of the other patterns mentioned in the paper. “People who have spent their careers studying this will either be in violent agreement or disagree with the proposals here,” says de Menocal. The model, however, is a “tremendous achievement in itself” and “gives you a model to ask these questions”.

Most researchers who spoke to temper nature We say that more evidence will be needed to prove that astrological cycles influenced the course of human origin. “If the solution to the puzzle of climate change and human evolution could be dealt with in a single paper, it would have been done 40 years ago,” Feith says.

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