Where our early ancestors wandered

On our People on the Move show, we heard about science challenging our understanding of when our earliest ancestors moved out of the African continent.

Mathew  - This traditional idea of this exodus out of Africa at around 50,000 years ago, isn't entirely correct. There is growing both archeological and fossil evidence to suggest that we dispersed out of Africa earlier, all the way to Northern Australia by around about 65 - 70,000 years ago. The picture is just becoming much more complex. It appears that we left multiple times, that there were disposals back into Africa. It's adding to this much more complex picture.

That was Mathew Stewart from the Max Planck Institute for Chemical Ecology, talking in particular reference to the amazing finding of what they reckon are homosapian footprints in an ancient former lake in Arabia, dated to around 125,000 years ago. And this jars with the idea of an exodus out of Africa happening around 50,000- 60,000 years ago, as was previously thought. So to find out what else science is revealing about how our ancestors moved around our planet, Katie Haylor spoke to Cambridge University's Emma Pomeroy...

Katie - That was Mathew Stewart from the max Planck Institute for Chemical Ecology, talking in particular reference to these amazing findings of what they reckon are homosapien footprints in an ancient former lake in Arabia. Emma, let's go back to you. What is the broad picture as we now understand it about how our ancient ancestors came to move around the world?

Emma - As was mentioned in that clip, for a while we thought that we didn't really spread out of Africa, which is where we first evolved, until relatively recently - by which we mean 50,000 years ago. But actually we're getting various lines of evidence showing that humans did spread out of Africa much earlier than that. But the question is how permanent were those migrations? So we've got some early modern human remains, for example, in Greece now dated 210,000 years ago. So sort of four times as old as we were thinking before, but there's no other evidence then for some time. So perhaps these are early dispersals that aren't successful colonizations.

Katie - Wow. That's an incredibly long time ago, it's kind of boggling my brain a little bit. But how do our modern ancestors homosapians, how do they end up on different continents? Because I guess there's just walking places, but what if you've got a mass of water in the way?

Emma - Yeah. Humans get remarkably early to, for example, Australia, where some of the earliest evidence now is dating to 65,000 years ago. And of course there's multiple large bodies of water to cross to get there from mainland Asia. So we assume that they must have had watercraft of some sort. We don't have any evidence of that. They presumably were made of organic materials so haven't preserved and any depictions of watercraft only come much later, but it's really the only plausible explanation for getting to parts of the world like Australia.

Katie - What about the Americas?

Emma - We used to think that humans only really got to the Americas perhaps about 10,000 years ago or a little more. And that they got that crossing from Siberia over a land bridge that was there at the time. However, some of the evidence that we're now getting suggests that those dispersals might have been much earlier. There was a recent study of evidence from Mexico that was dated to 26,500 years ago. Now one of the routes that we originally thought people must've taken was down the so-called ice-free corridor. So at that time, the land bridge was covered in ice sheets. And there were certain times when a corridor opened up that people could have walked down. But given that we've now got these quite early dates another hypothesis is that people actually went along the coastline.

Katie - Once you've got humans all over the world, what about when people start to settle? Do we know much about the transition between having a more kind of hunter-gatherer lifestyle and when you start doing things like farming agriculture?

Emma - Yeah, we do. And there's some really interesting evidence again coming from the archeology, but supplemented with ancient DNA, particularly to really understand what these processes were like. So for example in Europe and Asia, the domesticated plants and animals that people come to rely on as farmers, came from an area called the Levant in Southwest Asia. For a long time there was a big debate, was this moving into Europe by diffusion? Or was it actually farmers moving from the Levant actually migrating into Europe, bringing their farming techniques with them? The genetic evidence has been showing some really interesting things. So it does suggest that actually there was a migration of people into Europe and in some places they almost completely replaced the existing hunter-gatherer populations. There was a study of remains from the UK and it suggested that perhaps 90% of the original hunter-gatherer population was replaced by these incoming farmers.

Katie - What about the other hominins that were around at the time? Because we're not just talking about homosapiens are we really.

Emma - If you'd have asked that question 20 years ago, we'd have said, well, it was just modern humans and there were then Neanderthals in Europe and Asia and maybe another species called homo erectus still in Asia. But there's been really incredible discoveries over the last 20 years. So we now have another species called homo floresiensis that survived to about 50,000 years ago. There's also homo luzonensis on the Island of Luzon in the Philippines. Homo naledi was still around about 230,000 years ago in Africa. We've got Vende Denisovans, this kind of enigmatic species that were identified only initially from DNA in mainland Asia. And then we've also got evidence that homo erectus were indeed still around in parts of Asia, like Java, until around 110,000 years ago. So yeah, when we're looking at that initial dispersal period, Europe and Asia and Africa were occupied by a whole range of species closely related to us. And it's only much more recently that we've become the only ones that are left.

Katie - So there's far more to hominin movement than just homosapiens then. Emma Pomeroy thanks ever so much.