Professor Chris Turney, University of Exeter
Chris - Welcome to the Naked Scientists. Your work has largely been very exciting because you got to do things like date these hobbit people that were discovered a few years back but probably a lot of people are wondering where does man come from and could you possibly set the scene for us? Tell us what the time line is for the evolution of people on Earth and where we all came from?
Chris Turney - Yeah sure, Chris. Essentially the earliest remains of humans are in Africa about 2.5-2.3 million years ago. That’s a species called Homo habilis or ‘handy man.’ Apologies for the remarkably sexist names actually, it’s always man! But anyway, Homo habilis was the first species of our genus. After that it all gets a bit hazy. Traditionally it was always thought that an offshoot of that was Homo erectus (erect man). And the traditional view was that Homo erectus at some point migrated out of Africa and settled across different parts of the world: in Asia - Peking Man; Java Man down in Indonesia. In Europe he eventually evolved into Neanderthals. That was the traditional view and that’s the called the ‘Multiregional’ hypothesis which essentially is that these different species around the world evolved into us: Homo sapiens with a little bit of romantic liaisons on the edge. I wouldn’t say that’s the widely accepted view now but the more accepted view is the ‘Out of Africa’ hypothesis which is that our species (of which the earliest evidence is from about 200,000 years ago) evolved in Africa and then migrated out of Africa somewhere between 50,000 years to 100,000 years ago. They moved out across the world and essentially displaced all these ancient species of human.
Chris - Why do we think that that’s the case? Why have we changed our view that rather than evolving in-situ they actually had to come out of Africa twice?
Chris Turney - Well, there’s always evolution going on around the world all the time but essentially the species, our species, looks like the earliest evidence in Africa and nothing broadly comparable. I guess really, and we’ll come to that again, but the hobbit is also evidence of ‘Out of Africa.’
Chris - How do we know about that magic date of 50,000 years ago? What’s the evidence for that?
Chris Turney - Well, really it’s constrained really. We’ve got evidence of modern humans in Europe around 40,000 years ago (55-40,000ya). Really the lynchpin is essentially Australia actually. There’s not a lot of evidence of modern humans between Africa and Australia. There’s lots of stone tools but there’s very little modern human remains. There’s a little bit in Borneo and essentially it’s in Australia. Australia opens up all sorts of interesting angles because essentially even during an ice age when the sea level drops 120m, it’s always been an island. So people must have actually built boats to get across so the early stages therefore were 50-60,000 years ago.
Chris - So people were building boats 50,000 years ago? That’s really something isn’t it?
Chris Turney - Well, that’s right, We’ve got no direct evidence of it and, of course the alternative is a pregnant woman on a mat of vegetation or an elephant swimming across with people on him but I think basically a boats is probably a more likely one.
Chris - So tell us about the colonisation of Australia because that in itself’s an interesting story. Because people didn’t know exactly when the first settlers arrived there unless, I guess, you and your various techniques came along?
Chris Turney - Well, it’s been an interesting story actually. If you went back to the 1960s the earliest ages based on radio carbon dating were essentially around 10,000 years ago. And over time, gradually, it’s been pushed back and pushed back. Until about ten years or nearly 20 years ago now it was about 40,000. There’s a limit to radio carbon dating and 40,000 was traditionally quite close to how far back you can detect with that method. Then other methods came along and they started coming up with ages of 50 and 60,000. There was nothing close to that. So my research interest was really seeing if we could push back radio carbon dating and were those ages real artefacts of the method or were they real?
Chris - If we could just explore that a little bit, Chris – why is carbon dating restricted to those dates that you mention? Why can’t it go on ad infinitum?
Chris Turney - Well it all comes really down to this quirky concept called the half-life which essentially after a period of time half of your radioactive element disappears. So a radioactive carbon or C14 has a half-life of about 5,500 years. Every 5,500 years you lose half. After about seven or eight half-lives you’ve essentially got very little left. I guess the thing is if you took a piece of coal which is millions of years old and you added to that carbon 1% of something from your body (modern carbon) you’d come up with an age of 37,000 years if you measured that. That doesn’t mean the coal’s 37,000 years it’s just how far back it can really date.
Chris - How did you crack that nut?
Chris Turney - A combination of things. In Australia and South East Asia, probably lots of places in the world. Early archaeological remains, a lot of the artefacts are found associated with charcoal and charcoal’s great as there’s lots of it. It’s a product of burning. In many environments it can survive for quite a long time. The problem is it soaks up everything in the ground. If you’ve got smelly feet you can use a bit of charcoal. If it sits in the ground for 40,000 years it can pick up a lot of contamination so the method that we use was to clean up the carbon out of the charcoal and then we had a special vacuum line where we basically heated up the charcoal, burnt off all the contamination and cleaned up the sample for dating.
Chris - What did that show you about Australia?
Chris Turney - Well essentially when we actually tested it out, intriguingly some of the early sites became younger. Some stayed the same age but a few crucial ones actually became quite a bit older. One of them got back to around 52,000 years.
Chris - So that says people were knocking around Australia must have had the capacity to get across the water 50,000 years ago but also, what about the climate then? Obviously Australia’s struggling now with not enough rainfall, Murray Darling river’s down to a trickle because so much is having to be taken out for irrigation. Was it always like that?
Chris Turney - No. Australia swings backwards and forwards with aridity, all the time. Essentially, this is pretty unusual what’s happening at the moment. We’ve been doing a lot of work out there trying to reconstruct the climate and try and get a better handle on what’s happened in the past.
Chris - So what do you think has happened?
Chris Turney - Essentially, I think we’re in a lot of trouble unfortunately. We’re gonna have to start doing something pretty seriously.
Chris - But if you look at say, the timing of the arrival of people. One of the things that indigenous peoples in Australia have been doing for 40,000 years is burning stuff. So is there any evidence that they have brought about any of the change that you see in Australia?
Chris Turney - Well, some people have argued that. Yes we’ve done a lot of dating and looking at reconstruction of what vegetation was like and there does seem to be a coincidence between changes in vegetation, at least in NE Australia, and burning. So some people have argued that actually, human arrival caused catastrophic collapse of vegetation and it dried out. Other people disagree with that view. It’s an interesting debate going on.
Chris - If we could just turn finally to the hobbit story which was really exciting a few years ago. How do these hobbits, these little people fit into this whole picture of the colonisation of Australia and what else was going around the world at the same time?
Chris Turney - That was great fun. We were basically interested in trying to work out when Homo erectus died out across Indonesia and one of the early sites that we were interested in was led by a colleague, Mike Morewood ate the University of Wollongong. Mike was interested in the island of Flores and working with the Indonesian colleagues. He went back to one of the key sites that had been excavated before and there’d been burials found in the surface and lots of stone tools. Essentially when they were digging down they’re looking for Homo erectus. They came across an entirely new species of human, Homo floresiensis.
Kat - There’s been various arguments about whether it really is genuinely a new species or not. I’ve heard people say oh well it’s just a pygmy or something like that. How do we know that it is genuinely a new species, an offshoot?
Chris Turney - Well there’s quite a lot of evidence now presented in that shape of a skull, the shape of the whole skeleton actually, the pelvis and feet, the wristbones more recently and the brain size as well. Typically, if you look at the history of science as well, whenever a new species of human is discovered there’s usually some question about a diseased individual. When the first Neanderthal was found someone claimed it was a giant bear. Another person was a Mongolian Cossack. You’ve got lots chasing back Napolian in 1840. Another was that it was a child that suffered from rickets, got bashed over the head and a bit of arthritis. So it’s par for the course really.
Chris - Just looking briefly at the timeline, Chris. How many years were there hobbit people around on Earth?
Chris Turney - Well, some of their traits are remarkably ancient, possibly 2 million years or so. They certainly arrived in Flores by a million years ago and the most recent evidence we’ve got is 13,000 but there’s some tantalising stories from the locals, Ebu Gogo, the ancestor who eats everything and the locals insist that they arrived in the island just before the Dutch turned up a couple of hundred years ago. Mind-blowingly there might have been another species of human being on the island.
Chris - Thank you very much Chris Turney.
Chris has also written a book on this subject called Bones, Rocks and Stars: the Science of when things happened. This is currently available in hardback and will be out in paperback on November 13th.