MARY LOUISE KELLY, HOST:
Fire was crucial to our human evolution for cooking, protection, warmth.
AILSA CHANG, HOST:
And to make tools - a 2009 finding out of South Africa suggested our ancestors used fire to shape stone tools 160,000 years ago.
KELLY: Well, now scientists say it may have actually happened much earlier - 300,000 years ago. That's based on a study of rock shards in the Middle East.
FILIPE NATALIO: That was the challenge - trying to understand, from whatever these people left, what they were trying to do and what type of behaviors they have.
KELLY: That's Filipe Natalio of the Weizmann Institute of Science in Israel and lead author of the work in the journal Nature Human Behavior.
CHANG: His team chipped and flaked their own stone tools to study how they behaved in fire.
NATALIO: Oh, it was very exciting (laughter). It brought me back. Yeah, it was like a trip to the past.
CHANG: And they built a computer model which could accurately estimate the temperature those stones had been exposed to. Then they moved on to ancient tools.
KELLY: Which is where Israel's Qesem cave comes in. Early humans lived there 200- to 400,000 years ago. They left behind flint blades and smaller cutting tools called flakes.
CHANG: Natalio's team analyzed those bits of rock with their model. And they found that flakes were blasted with a wide range of high temperatures, but blades were only heated to lower temperatures.
NATALIO: And that, for us, was very striking because we were able to actually see behaviors that, when they wanted to produce one type of tool, they would use one type of approach. But then if they wanted to fabricate another type of tool, then they would use another protocol.
CURTIS MAREAN: And that's suggestive of controlled stone tool heat treatment - suggestive but not conclusive.
KELLY: Curtis Marean of Arizona State University - he was not involved in this work, but he was part of that South African study suggesting heat treatment happened 160,000 years ago. If these new findings are correct, it would double that, making this a much older innovation.
CHANG: And that has implications for early human brains too.
MAREAN: Because it's a complex technology, it's a signal that there's a cognition involved, either a modern cognition or getting close to being modern.
CHANG: For instance, Natalio says heating tools might require abstract thinking and planning ahead; in other words, the very tools that serve us so well today.
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