Once upon a time, there were six different species of early humans.

That's not science fiction, and they all belonged to the genus Homo, but only we Homo sapiens have survived. What killed  H. habilis, H. ergaster, H. erectus, H. heidelbergensis, and H. neanderthalensis? Nature exists to kill and birth so that seems a more likely culprit than conquest, and a new paper points the blame at one aspect of nature that dominated science media before the coronavirus pandemic - climate change.

The authors combined climate modeling and conclude that climate change and inability to adapt to either warming or cooling temperatures likely played a major role in sealing the fate of those other branches of humans. The climate "emulator" they used had temperature, rainfall, and other data over the last 5 million years. They also looked to a fossil database spanning more than 2,750 archaeological records to model the evolution of Homo species' climatic niche over time.

From there they projected how early humans might have reacted to changes in climate. They believe H. erectus, H. heidelbergensis, and H. neanderthalensis lost a significant portion of their climatic niche just before going extinct while Neanderthals did worse by evolutionary competition with H. sapiens. Many of us still today have Neanderthal DNA.

Obviously we can't predict the weather next week and there is uncertainty in climate modeling as well. There is even  uncertainly in paleoclimatic reconstruction of the past. When you add in the identification of fossil remains at the level of species, and the aging of fossil sites there are a lot of assumptions based on incomplete data, but this model is as good as any. Nature is still out to get us, so we continually have to adapt or die.

"Our findings show that despite technological innovations including the use of fire and refined stone tools, the formation of complex social networks, and - in the case of Neanderthals - even the production of glued spear points, fitted clothes, and a good amount of cultural and genetic exchange with Homo sapiens, past Homo species could not survive intense climate change," says Pasquale Raia of Università di Napoli Federico II in Napoli, Italy. "They tried hard; they made for the warmest places in reach as the climate got cold, but at the end of the day, that wasn't enough."