Neanderthals, our closest extinct relatives, roamed the Earth for about 300,000 years. They hunted, made tools, and lived amongst one another in complex social groups. But about 40,000 years ago, they disappeared.

What killed them has been a topic of tense debate for some years. “The issue of Neanderthal extinction is very complex, and very little is agreed upon,” Anna Goldfield, a doctoral candidate in archaeology at Boston University, told LiveScience. Was it climate change? Or a volcanic eruption? One theory even suggests that Neanderthals’ big eyes are to blame for their downfall.

But most researchers agree that modern humans had something to do with it. Indeed, within just 5,000 years of our arrival, Neanderthals had vanished. A new theory suggests that our mastery of fire is the key to why we thrived while they did not. “Fire use would have provided a significant advantage for the human population,” Goldfield said at the annual meeting of the Society for American Archaeology. 

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Aside from keeping us warm, fire allowed us to cook food, which has huge benefits, according to The Economist

“Cooking alters food in three important ways. It breaks starch molecules into more digestible fragments. It ‘denatures’ protein molecules, so that their amino-acid chains unfold and digestive enzymes can attack them more easily. And heat physically softens food. That makes it easier to digest, so even though the stuff is no more calorific, the body uses fewer calories dealing with it.”

It’s not that Neanderthals didn’t use fire — some of them did. Despite their historical portrayal as dimwitted cavemen, these hominids were masters of tool use, and archaeologists think they created sparks by striking flint against iron pyrite. And they did use fire to heat some of their meals. They even cooked with herbs

But Neanderthals may not have made use of flame as regularly or as efficiently as our ancestors did, according to archaeologist Dennis Sandgathe. Early modern human bodies were smaller and more efficient, which meant that cooked food was more beneficial for them. And the more that modern humans utilized the power of flame, “the more likely the human population was to increase slightly.” Over time, this disadvantage may have sealed the Neanderthals' fate.

As archaeologists continue to investigate, we’ll learn more about what really killed off our hominid relatives. “I suspect genetics will help,” says Richard Wrangham, an anthropologist at Harvard. “If we can pin down the genes underlying the adaptation to cooked food, we may be able to date the control of fire close enough to settle the big question.” Either way, the next time you turn your oven on to cook dinner, give thanks to the first modern humans for keeping the fire burning.