An Earlier Departure Out Of Africa?

A cache of stone tools found in the United Arab Emirates suggests that modern humans may have left Africa earlier — and via a different route — than previously thought. Anthropologist Will Harcourt-Smith describes the finding and how it may change thinking on human origins.

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IRA FLATOW, host:

This is SCIENCE FRIDAY. I'm Ira Flatow.

Most anthropologists agree that human evolution started in Africa and spread from there. But when did our ancestors venture out, and what route did they take? That's one of the biggest questions in human origins, and it's a question that sparked some really heated debate in anthropology circle.

And now there is some new information that could really heat up the debate and is, and helping some scientists fill in some of the blanks and raising, as I say, lots of questions also.

Researchers report this week in the journal Science that they have found an ancient toolkit in an unlikely place, and they're talking about the United Arab Emirates. The finding, they say, suggests that modern humans may have left Africa a lot earlier than anyone had thought, and their exodus may have taken a whole different route than what most people are talking about.

Here to talk about it with me is Will Harcourt-Smith. He is a research associate in paleontology at the American Museum of Natural History. He's also an assistant professor of anthropology at Lehman College in the Graduate Center at the City University of New York here in New York. Welcome to SCIENCE FRIDAY.

Mr. WILL HARCOURT-SMITH (Research Associate in Paleontology, American Museum of Natural History): Hi.

FLATOW: What is so interesting about this discovery? This pouch - was it a pouch or just a group of tools, just a bunch of tools found together?

Dr. HARCOURT-SMITH: That's it. It's just a bunch of tools. I mean, not just. They're incredibly important. But there are no skeletal remains of humans, fossilized remains.

The reason it's important is really twofold. It's an unusual part of the world to find these tools at this date.

FLATOW: What date are we talking about?

Dr. HARCOURT-SMITH: About 120,000 years ago. And in general, we don't find tools like that down in the Arabian Peninsula. This is way down in the Arabian Peninsula, not far - you know, as you said, in the UAE.

And conventionally, we think that modern humans emigrated out of Africa somewhat later, about 60,000, 70,000 years ago, through the Middle East, advanced, you know, into Europe and eventually sort of further east into Asia.

This implies that they may have taken a second route, which would have been through the Horn of Africa, straight into Arabia. And they've done a really neat bit of work here. They've not just looked at the stone tools, they've also looked at the sea levels and the geology, and they think that humans would have been able to get across at the straits there, right at Yemen near the port of Aden.

They would have been able to get - it's very narrow there anyway, and they would have been able to get across. So we're looking at a second route out of Africa, which is quite exciting.

FLATOW: But this theory is the newer theory, right?

Dr. HARCOURT-SMITH: Absolutely.

FLATOW: So, you know, as Carl Sagan used to say, extraordinary things require extraordinary proof.

Dr. HARCOURT-SMITH: They certainly do. He was absolutely right in that, in every respect. I think it's a really interesting find.

I mean, in a funny sort of way, it is exciting and new, but I would expect it because I think that to think that humans just went out of Africa just once, and there weren't other sort of forays or expeditions out or exoduses out, is probably a little over-simplistic.

FLATOW: So could this not have been, then, just a foray? Because we don't have any human skeletal remains there, right? There are no fossils of that person?

Dr. HARCOURT-SMITH: That's right. There are absolutely no fossils there. But it could easily have been more than just a foray. In fact, we find stone tools out in India. They've been found at sites in India, and they're dated at about 75,000 years ago. And that's a pretty new find. That came out in Science magazine in the last sort of four or five years.

And so if you've got these people coming out 120, maybe if they move slowly, you might expect to get finds further east and further east. And so maybe we do have to sort of revisit our views on this and sort of think about humans having left quite a lot earlier.

FLATOW: This whole time period is very interesting and what was going on with the humans or the humanoids or whatever that were living in that period because didn't we just hear about a genetic study that came out last year that showed modern humans mixing with Neanderthal?

Dr. HARCOURT-SMITH: Absolutely. It's an - that was really an amazing finding. And, you know, I love what I do because I never have to give the same lecture twice.

(Soundbite of laughter)

Dr. HARCOURT-SMITH: You know, the Neanderthals were always thought to be an absolutely separate species that the prevailing theory is they'd sort of died out about 30,000 years ago. And that there wasn't much admixture between modern humans and Neanderthals.

Along comes this genetic evidence that clearly shows that there was a small amount of admixture because we find a little bit of Neanderthal DNA in Europeans, in people from Melanesia and in people from eastern Asia.

And so we think that was happening about 60,000 years ago. This is way before that. And, of course, it's very much preliminary findings with the Neanderthal material, and it's only a very small part of the genome that they're looking at.

And so we have to be cautious about making too big a conclusion based on that. It's entirely feasible that modern humans got out before and got to various parts of the world, and then maybe the major exodus was later, at 60,000 years. And then we see perhaps, you know, admixture a little later on with those different modern human populations.

We see evidence of modern humans in the Middle East much earlier, at about 100,000 years ago. But we think they only just sort of forayed there and then retreated back into Africa.

FLATOW: But the tools that are found are of that age.

Dr. HARCOURT-SMITH: Absolutely, absolutely. And we also have human remains, fossilized, at about 100,000 in modern-day Israel. And we find that very nearby sites, or even sometimes the same sites, also (unintelligible).

We sort of think that Africa was this pump, where you've got sort of a modern human population, you've got Neanderthals in Europe and perhaps a little tiny bit of overlap just in the sort of Levant region.

FLATOW: You know, it's interesting because when you think of that area today, you're thinking of giant sand dunes.

Dr. HARCOURT-SMITH: Right.

FLATOW: How are these people going to get through that kind of stuff? But it wasn't like that back then, right?

Dr. HARCOURT-SMITH: It absolutely wasn't, and it's been very nicely shown in this paper that the environment was, it was very different. It was much wetter. There was much more vegetation, and there would have been many more sort of routes and possibilities, from a geographical perspective, for these peoples to sort of traveled along.

They could have traveled along the coast, as well, of course. There's been a lot of work showing that very nicely. So you - the sort of classic image of giant sand dunes of the Sahara, sure they were there in places, but it was a far more sort of fertile environment than it is today.

FLATOW: And the ocean levels were different.

Dr. HARCOURT-SMITH: And the ocean levels were very low, up to sort of many, many hundreds of feet lower. And of course, that meant that all sorts of places that today are islands were actually accessible and part of land bridges.

And so this one classic route out of Africa, through, you know, modern-day Egypt and Sinai, now it really looks like we may have another one going through the Horn of Africa, which I think is very exciting.

FLATOW: Does that open up - are scientists now girding up to go out and look for new stuff?

Dr. HARCOURT-SMITH: I hope so, and that's what it's all about. You know, you can find things out in two ways. You can look at existing specimens and come up with new conclusions, or you can go and find new stuff. And this is what these people have done.

And I hope it sort of precipitates a series of new expeditions and new endeavors in the Arabian Peninsula. We really, in the past, it's been rather barren in terms of findings, and I think this is very exciting, and it could be the tip of the iceberg.

FLATOW: If you - why would you find a toolkit without - I would imagine this would be very valuable to whoever had it because it took a while to make it.

Dr. HARCOURT-SMITH: Absolutely, yeah.

FLATOW: And so somebody left it behind, or what's the idea here that, out of nowhere, there's just somebody - maybe there was a pouch around that's gone, you know, it says Craftsman on the side somewhere.

Dr. HARCOURT-SMITH: You never know, probably unlikely, but you never know.

(Soundbite of laughter)

Dr. HARCOURT-SMITH: But no, you know, when we talk about toolkit, you know, they had different tools that could do different things, you know, tools for scraping, tools for cutting, tools for crushing. And in some cases, the tools that we find are things that maybe they left because they made more. Maybe they lost their sharpness.

You know, one of the things about, you know, tools - and they maybe didn't have the means to sort of maintain them in the way that we can maintain metal tools. So there could be ways that they left them and made more.

Sometimes, perhaps they weren't entirely happy with them, and they were discards. There's always that possibility with tools.

But of course, they're incredibly - the material they're made from is incredibly hard. You know, it tends to be sort of flint and cordite and that sort of thing, and they preserve extremely well as a result. So even if they died with them, sort of holding them, and for some reason their bones didn't get preserved, the tools do always last.

FLATOW: Let me just get a quick call in from Cathy(ph) in Rochester. Hi, welcome to SCIENCE FRIDAY.

CATHY (Caller): Hi, thanks, Ira. Yeah, I just - I was looking through, like, a general science book and there were - there was a listing of craters. So there's a crater in Ghana, I think they call it Bosumtwi Crater, from an impact around a little over a million years ago.

And I guess I just always wondered whether that could have been, like, some of the impetus for, like, erectus leaving Africa.

Dr. HARCOURT-SMITH: You never know. It's - there's an interesting question. Certainly climate plays a large role in affecting the behavior and expansion and retraction of different hominid species, sort of (unintelligible) human species.

The problem with that is that homo erectus left much, much earlier, left about 1.8 million years ago from Africa. So I would say it probably doesn't coincide with it, sadly.

FLATOW: Well, Dr. Harcourt-Smith, thank you for taking time to be with us today, fascinating.

Dr. HARCOURT-SMITH: Thank you very much.

FLATOW: And good luck at the museum.

Dr. HARCOURT-SMITH: Thanks a lot, bye.

FLATOW: Will Harcourt-Smith is a research associate in paleontology at the American Museum of Natural History and assistant professor of anthropology at the Lehman College and the Graduate Center of City University of New York.

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