A few million years

To kick us off on our journey through human history it would be good to know what we actually mean by human - our species the Homo sapiens, the Homo genus - a group that dates back around 2.5 million years or something else altogether? To help us navigate through the messy and political world of palaeoanthropology Chris Smith roped in our guests Lee Berger, Tomos Proffitt and Matthew Collins...

Lee - The genetic record, as well as the fossil record, correspond with an idea that around 6 to 7 million years ago, we split off from an ape somewhere in Africa and began a journey as bipedal apes (we call those the hominins or hominids). And that journey progressed in the old story, at least the simplified story, from first becoming bipedal, then we came down from the trees, we acquired at some point in there, tools. The brains got larger and we set ourselves up there for the origins of the genus Homo, which has typically been viewed as a big-brained species, using relatively complex tools, and that would lead in the last 2 million years or so to the origins of us.

Chris - So between 6 million and 2 million years ago what sorts of creatures - our human relatives - were there knocking around?

Lee - So in the earliest part of this we have creatures that go by the names such as ardipithecus, and then later the australopithecines or australopithecus. Those names aren't really so important. If you think of that earlier period, where you're thinking of something that is effectively more ape-like, traditionally thought of to have a smaller brain, and generally more ape-like bodies, but still bipedal, thick enamel, small canines - things that characterised hominids.

And then after that we had traditionally thought that there was larger brains, more complex tools, more complex behavior, long distance walking - these sorts of things. We've typically put those in the genus Homo.

Chris - What do you think made these sorts of individuals change over time and become ultimately us - what drove them to do that?

Lee - Well you could almost any paleoanthropologists and they'd probably give you a different answer to that. But, traditionally, we viewed it as ecological stresses, responses to the environment that would drive small changes, all these accumulating  to build micro changes in a lineage. But I don't want to give the impression of this being sort of straight linear line.

The idea you see of that t-shirt that you see of the evolving human from an ape to a human - that's wrong. And certainly the discoveries of last decades or so in paleoanthropology are showing that we can't view human evolution as simple.

Chris - Now Lee's got us up to roughly 2-ish million years ago, Tomas, so what happens between 2 million years ago and the sort of time when we're around?

Tomas - Well, it's at that point when you start to see stone tools being produced and it's a little bit before that. Very recently, last year, they found the earliest stone tools in Kenya and these are dated to 3.3, so they would have been around the same time as the australopithecines. Traditionally, up until last year, we see the very first stone technology and that has been seen as being associated with Homo habilis, so the first species of the Homo genus.

Chris - So from about 2 million years ago you get this genus Homo comes along and habilis, meaning handy, using hands to make stuff?

Tomos - Yes, absolutely. That stone tool technology stays with Homo habilis, essentially, for around a million years, a bit over a million years. Until you see the onset of the ashmolean, which is a more complex technology but that coincides with the emergence of Homo erectus or ergaster in Africa.

Chris - And that's what? A million years ago?

Tomos - No about 1.7, 1.8 million years ago.

Chris - And then Homo erectus carries on?

Tomos - Absolutely.

Chris - And does that then hand on, Matthew, to Neanderthal - where do they fit into the picture?

Matthew - It was quite simple in the past because we had the Neanderthal and then the modern's come in, and the moderns come in and they wipe the Neanderthals out.

But the things I'm interested in are the molecules. Now the molecules are starting to tell a new and different story because what we're now seeing, of course, first of all is that inside us, we have bits of Neanderthal. But, in addition, there's another group that's been discovered from molecular data, called the Denisovan. And there's even been some hints in the last couple of weeks of another species based entirely on the DNA found in hominid, so-called species X. So, in fact, the story, which was quite simple, seems to be getting evermore complicated.

Chris - Lee - yes do summarise and try and draw these strands together for us...

Lee - I think an important point that comes out of what's been led in here is that we thought we had a very simple record. We thought we had in figured out and archeology seemed to correspond with the fossil record. What I think has been overlooked by paleoanthropologists, archaeologists and, perhaps, the public as well, is the idea that we had almost no direct association of these tools and this archaeology and these cultures with the physical species. We've just assumed that there's just one species at one time, that the fossils that we find in a particular area, broadly in the same time, belong to a particular archeology and yet, that may not be true. As recently as fifteen years ago, I could sit in a conference where you would hear senior scientists say there was only one species living at any one time in the past within our lineage. That was wrong.