Our Hunter-Gatherer Past

Genetics and new insights into our past

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Michael Warby joins us to talk about some fairly recent books that explain what we're learning about the history of homo sapiens from the analysis of genetic material.

Michael Duffy: Our next guest is Michael Warby, he's a Melbourne writer and teacher and he talks to us from time to time about interesting ideas in the worlds of academia and more serious book publishing. Michael, welcome back to the program.

Michael Warby: It's a pleasure to be here.

Michael Duffy: Tell us, what's today's subject?

Michael Warby: Today's subject is using genetics, the study of human DNA to understand our pre-history a lot better.

Michael Duffy: And this is something that's been a pretty big deal in the last few years. Can you tell us about some of the books that you'll be mentioning?

Michael Warby: Basically concentrating on three books. One is Luigi Luca Cavalli-Sforza's Genes, Peoples and Languages, and this was published in the year 2000. Cavalli-Sforza is the doyen of using genetics to understand human pre-history. There is Bryan Sykes's The Seven Daughters of Eve: The Science That Reveals Our Genetic Ancestry. Bryan Sykes was the lead researcher in the famous Ice Man case. His team developed the technique for identifying DNA from old skeletons like the Ice Man, specifically by examining their teeth. And the last one is Nicholas Wade's Before the Dawn: Recovering the Lost History of Our Ancestors. Nicholas Wade is a science journalist for the New York Times, he has a very good eye for how to explain things and also for the juicy bits, the violent bits and the striking bits. But they are all very clear writers, that's something they've all got in common.

Michael Duffy: Can you tell us, just as a sort of introduction to the subject, how can our genetics tell us anything about our past? It's an interesting proposition for someone who hasn't really thought about it.

Michael Warby: It's perhaps not so surprising in that if you can get a 15,000-year-old skeleton and dig into its teeth and get its DNA that that might tell you something. What is really striking is that by looking at modern humans you can tell a lot about our past because as long as you assume a certain standard rate of mutation in DNA, you can look at how long it has taken a particular genetic strand to differentiate itself from another genetic strand, and you can look at what the genetic traits in people are doing. The business about the mutation rate being fairly standard is an assumption, which is why all these three writers talk very much about how you use information from other disciplines to check your results. So it's very much about using genetics as a part of an interdisciplinary approach to understanding pre-history.

But to give an example from relatively recent news; Mad Cow disease in Britain. There should have been, in effect, a lot more deaths from Mad Cow disease than there were, and thankfully there were not, but the reason there was not was because it turns out that many people have genetic protection against Mad Cow disease. Why do they have that? Well, because they had cannibal ancestors. There were certain diseases you were likely to catch from eating fellow humans and so there was a selection process in favour of protection against those diseases. So if you had the right genetic markers you were much, much less likely to get Mad Cow disease.

Michael Duffy: Because this also protected you against that, presumably?

Michael Warby: Yes, it was a variation of the same problem.

Michael Duffy: Something I found fascinating when I was talking about this a bit earlier is that we're not just looking at the genes of humans necessarily, also the genes of associated animals can be instructive. Tell us about lice.

Michael Warby: Yes, the lice is a great case. When we had body hair all over our bodies we had lice. They've now become restricted to essentially head lice because that's essentially the only area we've got a large amount of hair left. When we lost our hair we started using clothes, then developed body lice which lives in clothing. By working out how long ago it was that head lice differentiated themselves from body lice, you can work out how long ago it was that humans started wearing clothes, and it turns out it was about 72,000 years ago, so that's roughly when we lost our body hair.

Michael Duffy: That's pretty good, that's a pretty amazing way of finding out when people started wearing clothes.

Michael Warby: Yes, it's great stuff.

Michael Duffy: Can you just tell us some of the other things that we now feel fairly confident about in the history of homo sapiens thanks to genetics? How long ago did homo sapiens appear, for example?

Michael Warby: We're fairly confident that anatomically speaking about 100,000 years ago. There's an interesting feature to this which is that about 50,000 years ago, homo sapiens started behaving like modern humans, they started doing things like art, burying their dead, science, religion, language and so forth, but there's quite a gap between the big anatomical change when we got specifically homo sapiens in an anatomical sense...it took about 50,000 years before you get homo sapiens who are behaving in recognisably modern ways, and it's an interesting question about what's going on there. Another thing we are extremely confident about nowadays is that humans came out of Africa. The African origin of homo sapiens is fairly overwhelmingly established now and genetics is certainly one of the ways in which that is established.

Michael Duffy: So in some cases this is confirming things that we'd already thought about from archaeological or fossil evidence.

Michael Warby: Absolutely, but there was a long-running debate about whether humans evolved at a particular spot or they evolved at various places around the planet and sort of merged together. It's fairly clear now from the genetics that they evolved in Africa. So we're an African species.

Michael Duffy: And of course we started using tools about two million years ago...

Michael Warby: Yes, homo erectus, our predecessors, yes.

Michael Duffy: Homo sapiens emerge 100,000 years ago. What sort of changes do we think might have occurred to us genetically in that period? How long does it take for evolution to occur?

Michael Warby: That's one of the fascinating things about evolutionary history. It's not an even-handed process, it happens in fits and starts. They've even got a term for it now, they call it 'punctuated equilibrium'. And so you've got this history of how many...you know, our ancestors split off from the other primates two million years ago, something like that, and it took two million years for the homo branches to eventually produce homo sapiens 100,000 years ago. While human evolution is continuing, there have not been any dramatic changes in the last 100,000 years in our physical and genetic structure, but there have been some interesting shifts. We have got more what they call 'gracile', so we've got more delicate. The difference between the size of men and women has shrunk. These are both signs that homo sapiens have got significantly less violent.

Michael Duffy: Oh really? That's a very interesting thing in itself, isn't it?

Michael Warby: Deeply interesting, yes.

Michael Duffy: This is not just a cultural thing, we think it's a genetic thing too?

Michael Warby: Well, it's interaction. The thing about homo sapiens is that our great evolutionary niche is essentially cognition. Other animals think but we are, by any standards, much more about interaction in terms of language, of facial expressions, body, our level of interaction is so much greater. And how genetics support that is we are surprising malleable. We have a very long childhoods, we are very vulnerable during that childhood and that makes us more malleable in ways which allows us to absorb a lot of information, to pick up different cultures in different ways, so we're set up to be varied, if you know what I mean.

Michael Duffy: Let's come back to the point that we are a bit less violent than we were. Some people would say the 20th century was a fairly violent century, but how does it compare with the past?

Michael Warby: Well, it depends on whether you mean numbers...I mean, you've got to realise that the population of the world went up in the last 100 years from one-point-six billion to over six billion. Obviously a proportion of six billion people is going to be a lot of people, but if we in the 20th century had had the rate of violence that hunter-gather societies typically have, our war dead in the 20th century would have been something in the order of two billion people. Obviously that's many more...that's at least in order of magnitude than the actual number of war dead. It is a striking thing that each broad stage of human history...so hunter-gatherers seem to be significantly more violent than farmers, industrial societies significantly less violent than agricultural societies. So there's been a process of less violence, of what you might call domestication of humans.

Michael Duffy: I'm just interested in what evolution might be happening at the moment. I suppose this is highly speculative but I suppose we are still evolved hunter-gatherers living in a very different circumstance, living in cities for most of us. Would there be some evolution going on now, I suppose, that we don't know about, that those of us who are better adapted to living in cities, whatever that means, may have a better chance of surviving than those of us who are hunter-gatherers or more violent or whatever?

Michael Warby: It's a fascinating question. We do know that the genes of humans are getting healthier. The reason is that they're mixing more. Mixing discourages regressive...it discourages bad genetic traits, so mixing is good. So yes, for sure there is selection going on. How strongly? That's an interesting question because it's going to affect...selection occurs from inheritance so it's basically about who has children, how many children, where they have children and so forth. There may, for example, be selection going on (and this may sound a bit odd) for religious belief.

Michael Duffy: It's possible we might have to wait another 50,000 years to sort that one out. I'm afraid we're out of time, we'll talk again soon. Thanks, Michael.

Michael Warby: No problem, my pleasure.

Michael Duffy: That was Michael Warby, who is a Melbourne teacher and writer.