Record-breaking simulation tips on how the climate shaped human migration, news and research
A colossal simulation of the last two million years of the Earth’s climate provides evidence that temperature and other planetary conditions influenced early human migration – and possibly contributed to the emergence of the modern human species about 300,000 years ago.
The finding is one of many that have come out of the largest model to date to investigate how changes in the earth’s motion have affected the climate and human evolution, published in Nature today. “This is another brick in the wall to support the role of climate in shaping human ancestry,” said Peter de Menocal, director of the Woods Hole Oceanographic Institution in Falmouth, Massachusetts.
The idea that the climate can play a significant role in human evolution has been around since at least the 1920s, when scientists began to discuss whether drier conditions had led to early human ancestors beginning to walk on two feet to adapt to life on the savannah. But so far, scientists have struggled to provide strong evidence that the climate played a role in shaping humanity.
In the latest study, Axel Timmermann, a climate physicist at Pusan National University in South Korea, and his colleagues ran a climate model on a supercomputer for six months to reconstruct how temperature and precipitation may have shaped what resources were available to humans in the past. million years. Specifically, the researchers examined how long-term fluctuations in the climate as a result of the Earth’s astronomical movement may have created the conditions for stimulating human evolution.
The pressure and attraction of other planets changes the Earth’s climate by changing both the planet’s inclination and the shape of its orbit. During 41,000-year cycles, the earth’s slope fluctuates, affecting the intensity of the seasons and changing the amount of rain that falls over the tropics. And over 100,000-year cycles, the earth goes from having a more circular orbit – which gives more sunlight and longer summers – to having a more elliptical orbit, which reduces sunlight and can lead to periods of ice formation.
Timmermann and his colleagues used a simulation that incorporated these astronomical changes and then combined their results with thousands of fossils and other archaeological evidence to find out where and when six species of humans – including the early Standing man and the modern Homo sapiens – could have lived.
Movements and mixing
The study pumped out a staggering amount of data and Timmermann says that several interesting patterns emerged. The researchers’ analysis showed, for example, that an early human species, Homo heidelbergensis, began to expand its habitat about 700,000 years ago. Some scientists have thought that this species may have given rise to a host of others around the world, including Neanderthals (Homo neanderthalensis) in Eurasia and H. sapiens somewhere in Africa.
The model suggests that the distribution of H. heidelbergensis across the globe was possible because a more elliptical orbit created wetter climatic conditions that allowed the species to migrate wider. The simulation also showed that the most habitable regions, in terms of climate, changed over time, and the fossil record followed.
“The global collection of skulls and tools is not randomly distributed over time,” says Timmermann. “It follows a pattern” that overlaps with climate change driven by the movement of the earth. “This is amazing to me – here’s a pattern no one has been able to see so far.”
Part of this pattern can provide new insight into where and how our own species originated. Some genetic studies of contemporary hunter-gatherer groups in sub-Saharan Africa – which tend to be genetically isolated – suggest that H. sapiens is the result of a single evolutionary event in southern Africa. But other studies point to a more complex history, in which humanity began as a hotbed of many different groups of ancient Africans who together developed into modern humans.
Timmermann and his colleagues say that their climate reconstruction favors the hypothesis of a single evolutionary path. The model suggests that our species evolved when H. heidelbergensis in southern Africa began to lose living habitats during an unusually hot period. This population could have developed into H. sapiens by adapting to the warmer, drier conditions.
But this finding is unlikely to end the debate. “To claim that a particular climate event led to a species formation event is really difficult,” in part because of gaps in fossil and genetic data, “said Tyler Faith, a paleobiologist at the University of Utah in Salt Lake City.
The same applies to many of the other patterns reported in the newspaper. “The people who have spent a career studying this will either violently agree or disagree with the proposals here,” de Menocal said. However, the model is a “phenomenal achievement in itself” and “gives you a template to ask these questions”.
Most researchers who spoke with Nature say that more evidence will be needed to prove that astronomical cycles affected the orbit of human descent. “If one could solve the mystery of climate change and human evolution in one document, it would have been done 40 years ago,” says Faith.
That’s why Timmermann and his colleagues plan to run even larger models, including those that integrate genetic data.
This article is reproduced with permission and was first published on April 13, 2022.