What is Archaeogenetics?
Kat - Now this week, we're looking at the science of archaeogenetics where modern genetic techniques are used to compliment traditional trowel-in-the-soil archaeology and we're really honoured to have with us Professor Lord Colin Renfrew who's a Cambridge University archaeologist and he's credited with being the person who coined the phrase "archaeogenetics." Hello, Colin.
Colin - Hello.
Kat - So, we tend to think of archaeology as people on their hands and knees digging with trowels in the soil. How does archaeogenetics work? How do we meld modern genetics with these kinds of archaeological studies?
Colin - Well the remarkable thing is that most of what we've learned from archaeogenetics actually comes from specimens, blood specimens or genetic specimens, taken from living populations. The remarkable thing is that because the mitochondrial DNA is much the same from one generation to the next or the Y chromosome DNA much the same from one generation to the next, there's great stability. By comparing living populations, it's possible to construct trees which, it seems, give a very persuasive account of human decent. On the other hand, it is possible to take specimens from long dead humans and look at their DNA, the ancient DNA. But that is a much more difficult technique and the picture we have of the out of Africa migrations of our species around 60,000 years ago essentially comes from mitochondrial DNA taken from living people who are with us today or just of recent decades.
Kat - So let's look at a little bit more of that mitochondrial DNA because obviously, when humans are made by mommy and daddy, you mix mom and dad's chromosomes together, but why is mitochondrial DNA so special for these kind of studies?
Colin - That's right. You've put your finger on it as you say, most DNA - nuclear DNA is a mixture of the DNA from the mother and from the father. But the mitochondrial DNA is passed on in the female line. So your mitochondrial DNA comes from your mother and hers from her mother and so on, and indeed mine comes from my mother and from my maternal grandmother. So it goes down in a single line in that way, a single lineage. There is very little variation and less mutations which happen infrequently. So there's great stability and in this way, one can go back up the lineage as it were, studying those mutations, and getting overall, a picture which has led to the conclusion, and part of the conclusion comes from this work, that our species must have originated in Africa something like 200,000 years ago and all of us humans are the result of migrations out of Africa, something like 60,000 years ago.
Kat - So I've read about things like the original Eves and this is because you can follow the mitochondrial DNA up the female line. How far back can we really go? Could you almost pin-point one person or is it more just groups and populations?
Colin - It's a group certainly. One wouldn't want to pin-point one person although that may be theoretically possible. Well, you can go back to 200,000 years ago and that would be one of the very first humans of our species, Homo sapiens but you can of course go further up the decent line where you get to the point where our species began or the ancestors of our species began to separate out from the Neanderthals, something like half a million years ago.
Kat - And as we've heard, maybe not quite as separate as we previously thought.
Colin - Yes. Well that's a very interesting new discovery. The mainstream idea hitherto has been that our species, Homo sapiens, emerged out of Africa something like 60,000 years ago. And so, it's very exciting that there may have been Neanderthal survivors who may have made contributions to the Homo sapiens' genetic gene pool, very exciting discovery.
Kat - So we've discussed how we can follow the maternal line, follow the women by looking at mitochondrial DNA. What about the chaps, because obviously, you have a Y chromosome. Is that as useful or is it less useful?
Colin - Yes, it is as useful and it's been more difficult to do so the research has come about more recently but the Y chromosome has been extremely important because the non-combining part of the Y chromosome passes down exclusively in the male line. So in a way, it's rather a mirror image of what you'll find on the female line with the mitochondrial DNA. The only problem is that the chronology isn't secure. Dating is very difficult in genetics and there is less confidence about the precision of the Y chromosome DNA dating. But certainly, it gives a parallel picture which broadly supports the conclusions that have emerged over the past 10 or 15 years from the mitochondrial DNA.
Kat - And the sort of things that you're finding through studying DNA, studying mitochondrial DNA and Y chromosome DNA, how do you actually anchor them to a real life archaeological timeline and do you ever find that it disagrees with the archaeological timeline?
Colin - Well somehow, the research works to try and bring them into relationship. For instance, the mitochondrial DNA dating seems to correlate fairly well with the fossil record. For instance, we have the first humans in Australia, something like 50,000 years ago, and that ties in quite well with the out of Africa migration along the southern coasts of Asia so that humans reached Australia something about 50,000 years ago and the pattern works well. It works also in the Americas where it seems that our species reached North America something like 15,000 years ago or maybe a little more. So that the archaeology and the DNA do harmonise together to some extent, but as I say, it's only more recently that ancient DNA from actual fossil humans has been brought into play.
Kat - And do you find that really ties everything together and helps you to anchor points of this timeline?
Colin - Well it's certainly beginning to if we're looking for instance at the population history of Europe. When we look at Neolithic remains, and there one can get skeletons and look at the DNA, usually, the mitochondrial DNA which is usually better preserved, one can look at the haplogroups and begin to put together a story there. But there are quite a lot of problems and I don't think everything is yet clear. This discipline is obviously in its infancy and it has enormous potential because the data are abundantly rich or will be abundantly rich. But there are still quite a lot of problems of interpretation. For instance, if we're looking at the origins of language families, there's a lot of argument about that at the moment which it was hoped DNA might solve very rapidly. But the solution hasn't quite yet come, though I think it's on the way.
Kat - Just very briefly, what really intrigues you? What's the mystery that you really want to get your teeth into?
Colin - Well I myself would like to get clear on what are the origins of the Indo-European language family and that's difficult to determine probably because we're talking about languages there. And there are two main theories. One is that this language family might have emerged out of Anatolia with the coming of the first farmers to Europe. And there's another theory that it may have been to do with the domestication of the horse in the European steppes which have put it at a much later date. But to bring the DNA and the archaeology and the linguistics together successfully is quite complicated and I don't think we've quite got there yet.