I need to say from the start — I am an astronomer, not a biologist, and in discussing this paper, I am trusting more than ever in the peer review system. The paper we’re discussing appears in Nature and was read by a group of experts who reviewed the work, asked questions, and, if this went as the normal peer review goes, may have even asked for a new analysis of the findings from new directions that made the results even stronger.

So, here we go. 

Our planet has a bit of a tilt, and like a spinning top, how that tilt is pointed can change with time. With that change, the details that define our climate can change. Right now, our planet is closest to the Sun in January when the southern hemisphere is in the heat of summer and the north sees winter. As things wobble, that will change. So will other things. And the result is changes to where we see and don’t see glaciers and tropics and how the seasons change. 

Different people like different temperatures, and that has always been true. It was especially true when there was more than one kind of human on Earth. We are Homo sapiens, and there is evidence of two other species, Neanderthals and Denisovans, that once shared the world with us. All three species branched off from the earlier Homo heidelbergensis.

And here is where it gets cool – or hot – depending on which species you’re tracking. Each of these peoples preferred different temperatures, and as our world’s climate changed, these people moved with the weather. A group of researchers led by Axel Timmermann pieced this story together by looking at both the fossil record and long-term climate models side by side.

According to Timmermann: Even though different groups of archaic humans preferred different climatic environments…This result implies that, at least during the past 500 thousand years, the real sequence of past climate change, including glacial cycles, played a central role in determining where different hominin groups lived and where their remains have been found.

Genetically, we know that there has been some mixing between all three of these populations. But how much did they really interact? That depends on how much the weather for the different groups crossed. Study co-author Pasquale Raia explains: The next question we set out to address was whether the habitats of the different human species overlapped in space and time. Past contact zones provide crucial information on potential species successions and admixture.

From their climate models, they matched results we’ve also seen in genetic studies. The Neanderthals and Denisovans appear to have evolved from the Eurasian populations of Homo heidelbergensis. Homo sapiens came instead from the south African population.

This work also looked at early populations, pre Homo heidelbergensis. In looking back further, co-author Elke Zeller explains that those earlier humans back one or two million years ago preferred stable climatic conditions. This constrained them to relatively narrow habitable corridors. Following a major climatic transition about 800 thousand years ago, a group known under the umbrella term Homo heidelbergensis adapted to a much wider range of available food resources, which enabled them to become global wanderers, reaching remote regions in Europe and eastern Asia.

As Timmermann puts it: Our study documents that climate played a fundamental role in the evolution of our genus Homo. We are who we are because we have managed to adapt over millennia to slow shifts in the past climate.

While they never come out and say it, I love the implication that being able to deal with lots of different climates was the thing that made our ancestors more evolved. Next time someone teases me for living someplace with snow, tornadoes, and summer heat, I’m just going to say it’s a sign I’m more evolved.

More Information

Institute for Basic Science press release

“Climate effects on archaic human habitats and species successions,” Axel Timmermann et al., 2022 April 13, Nature

VIDEO: Climate effects on archaic human habitats and species successions (IBS Center for Climate Physics)