Kat - We're no going to speak to Dr Anne Skinner who's from William's College in Massachusetts. Good evening Anne.
Anne - Hello.
Kat - Now, I understand that you've been studying how humans have used fire in history. So can you put it in a bit of context? How far back did we previously think humans have been using fire?
Anne - Prior to the work that I did a few years ago the earliest of dates for fire were about 300,000 years ago. That is, controlled use of fire by human beings.
Kat - So we're talking about camp fires here, basically?
Anne - Yes, yes.
Kat - What have you done now?
Anne - So what I did, about in the 1980s some bones were found in Swartkrans Cave which is in South Africa. They'd clearly been burnt. The layer in which they were found was dated to about 1 and a half million years ago and the question was, 'how did these bones get burnt?' And, 'could that be evidence that they were deliberately burnt as a result of human activity?' So I used a technique that's called electron spin resonance - we won't have to spend a lot of time on that - to look at the remnants of the burning process. If you burn something long enough you get soot. But if you don't burn it quite long enough you have some other organic materials in it. And the actual ones that you find will depend on how hot the fire was.
Kat - So will that be the difference between whether it was a campfire or say, just an accidental bush fire?
Anne - Right. Because at the time it was not a forested area. If it was an accidental fire it would be a grass fire about 300 degrees centigrade maximum. Camp fires go easily up to 500/600 degrees centigrade. So if these bones had been heated well over 300 that would suggest that the fire that had heated them had been deliberately assembled by the people who were also assembling the bones.
Kat - So it was basically a barbecue?
Anne - Not really, there's no sign that they were cooking. This has been billed as the earliest barbecue or as South Africans call it, a braai. First of all, if you actually cook something to 600 degrees centigrade it isn't fit to eat any more.
Chris - I dunno, you've obviously not tried my wife's cooking, Anne.
Anne - Also, you couldn't have counted on having the fire all the time. That is, probably what happened was that there was a lightning strike, some bushes caught of fire and they dragged burning wood back to the cave and used it to protect themselves against the leopards which were around.
Kat - That would suggest that humans were using fire one and a half million years ago. That's quite a dramatic difference from 300,000.
Anne - It is. Oh yes! In some ways it's not that remarkable if you stop to think that 1.8 million years ago some of our other ancestors were as, Chris was saying, migrating up into the Caucasus and I know climate was milder there. But I'm sure they would have appreciated having at least some knowledge of the properties of fire in the winter time in the Caucasus.
Chris - Thank you very much Anne, it's brilliant to hear your work.