How has the study of human molecular genetics contributed to our understanding of prehistory?
Genetic analysis of living humans links us directly to our ancestors in the past. But it does not show us ancient humans who failed and went extinct.
Archaeology achieves the opposite: it analyses only the past, and therefore gives a full picture of that past, but cannot tell us which human lineages survived until today and which lineages went extinct.
For example, DNA analysis shows that in Latin America, the male lines have largely been replaced by European males, whereas the female Native American lines are still in the majority in much of Latin America. So genetics and archaeology are complementary to each other in understanding our prehistory. And since 2005, ancient DNA analysis directly on ancient human remains is closing even this gap between archaeology and genetics.
Why are the details of how, when and where humans evolved across the planet so contentious among geneticists?
It came in a flash, and I was overwhelmed at rediscovering something that had been forgotten for 60,000 years.
I actually doubt that the genetic results are contentious among geneticists.
Allan Wilson published in 1987 that humans arose in Africa some 200,000 years ago, and although his data analysis was criticised on technical grounds, his results have stood the test of time.
Similarly, when Antonio Torroni and Douglas Wallace showed in 1994 that there is no Neanderthal DNA in modern Europeans, no eyebrows were raised. And when my own team concluded that a single small group of humans left Africa, and only 60,000 years ago, to colonise the rest of the world, it became the standard scenario with no criticism, as far as I am aware.
What are the greatest challenges that you face in your research?
The older I get, the more critical I become of the quality of my research: publishing even a single mistake can mean being thrown to the lions. It slows progress to check everything dozens of times. But my colleagues and I have not shrunk from correcting the mistakes of others (we discovered in 2003 that more than half of published papers contain DNA data errors, and also the data analysis is often only black magic and wishful thinking), so I suppose it is only fair if I feel the heat myself.
What inspired your interest in human origins?
Two attractions have come together: one the one hand I have been fascinated even as a child why some societies fail while others succeed. What is the reason? Can studying the past give us a clue? And my other fascination has been about immortality: as individuals, we will pass away and return to dust in the twinkling of an eye.
Astronomy, archaeology, history, theology and evolutionary genetics however deal with much more substantial timescales. Hence these disciplines hold a fascination for people like me. I even suspect that anybody interested in short –term phenomena (like clothes or car fashions) will probably not become a full-blooded cosmologist, archaeologist or evolutionary geneticist.
In one of his last papers before he died of leukaemia, Allan Wilson urged geneticists to improve the concept of the “molecular clock”, with which we can date prehistoric genetic events to look far back into the past, and reading that paper as a student touched a button in me.
The Cambridge World Prehistory brings together many different disciplines to reveal a rich history of human existence. Which other fields/areas/approaches/disciplines do you come into contact with most as a molecular geneticist and why?
Initially, in the early 1990s, I think I followed climatology most. At the time, illustrious human geneticists tried to explain human genetic variation with known Greek colonisation of the Mediterranean, or Arab invasions of North Africa.
Colin Renfrew pushed the boundaries far back when he said that the first farmers shaped who we are today. And then I started wondering whether some of the genetic variation we see today might have their roots even further back in the Ice Age. My professors in Hamburg discouraged me, thinking that migration must have obscured everything, but somehow I was sure I was on the right track.
Your contributions to the World Prehistory draw on a wide range of scientific research techniques and datasets. Can you explain the main (OR most exciting/interesting OR the latest) techniques and data forms used as evidence in your field?
Our early work was on female lines (the mtDNA), simply because in the 1990s people had not yet discovered informative sections of the male-inherited Y chromosome. Now, the situation has reversed: the team of Peter Underhill (Stanford) started unlocking the Y chromosome, and so did forensic genetics, discovering highly informative sections.
It turns out that the Y chromosome traces recent prehistory (centuries to millenia) much better than mtDNA, whereas mtDNA usually has survived better on a scale of tens of millennia.
The explanation might be human reproductive behaviour: invading males kill or marginalise resident males but marry into the local females.
Can you describe one or two key findings / interesting case studies from your contributions to the Cambridge World Prehistory and why they are important to the field of archaeology?
Some of the major historic events, especially the prehistoric spread of languages, can now be understood using the Y chromosome, where the mtDNA could not tell us anything. This is because languages are transmitted more typically by males than females, at least during prehistory.
We (and that is explicitly including myself!) were fooled for a long time by the intuitive notion of a “mother tongue”, until the truth dawned upon us in 2011, while I was compiling data to write the chapters in the CWP.
What are the breakthrough/pioneering studies that have influenced/inspired you the most in your research? (this could be your own breakthrough moment, or a pioneering study in the field)
Doubtlessly Allan Wilson’s paper of 1987, tracing the common female ancestor to Africa some 6000 generations ago.
How do your contributions to The Cambridge World Prehistory fit with your wider research and interests?
See above, the CWP work inspired my “father” tongue discovery.
Can you describe a breakthrough moment in your research?
In the summer of 2000, my wife and I were staying in a house on a lake in northern Germany, and I tended to get out of bed relatively early to analyse the worldwide human mtDNA data I had compiled over the years.
It suddenly struck me that morning that only one group of humans had ever successfully migrated out of Africa, that that group was tiny (less than 200), and that everyone outside Africa, whether Australian aboriginal or Icelandic Viking, was descended from that emigrant group, that the emigrants looked like black Africans, and that the racial differences we observe outside Africa today arose less than 60,000 years ago.
It came in a flash, and I was overwhelmed at rediscovering something that had been forgotten for 60,000 years (2000 generations!).
The conclusions sound trivial now, but back in 2000, researchers still tried to explain the different human races outside Africa with several African migrations – light skinned north Africans moving north, another set of darker-skinned emigrants hugging the equator and so on. Anyway, after that exciting moment, it became very tedious for me to write up and publish the conclusion, because once I have discovered something, I do not feel an urge to communicate it, and writing becomes a chore.
Was there any one scientist/geneticist who OR book which ignited your interest in the field?
One is Allan Wilson’s 1991 paper, discovering our Afican mitochondrial Eve, and the other book which left a lasting impression is Colin Renfrew’s Archeology and Language – the Puzzle of Indo-Eruopean Origins, which I read while visiting my colleague Martin Richards in Oxford while I was still a chemistry student.
What fascinated me about Colin Renfrew’s book most was not so much his Indo-European theories, which made sense to me and were therefore unremarkable, but his chapter on ruthlessly taking apart the traditional notion of a Celtic people. It showed me how even learned people can accumulate errors and misconceptions over the centuries, ultimately resulting in fairy story over one or two millennia.
That was a valuable lesson.
Genetics and archaeology are complementary to each other in understanding our prehistory
Which aspect(s) of your day-to-day research (and/or which aspects of your work in archaeogenetics) do you enjoy the most?
I still like the moment when painstakingly accumulated data over many years suddenly leads to new conclusions. The excitement grows less the older I get however, because you begin to expect to make important discoveries, and in fact are disappointed when it does not happen, or when others have arrived there faster than you have.
Describe the importance of your research in no more than 140 characters….
Combining genetics, climate, archaeology and language into one prehistory of humans in the past 200,000 years.
What’s the one conference you would never miss?
I enjoy being invited to different conferences – archaeology, linguistics, forensics, genetics, most recently a workshop on developing guidelines for DNA ancestry testing, which is one of my activities.
There is no single conference series which covers the breadth of fields. For pure enjoyment, I would probably choose an archaeological conference.
Do you have any advice for anyone hoping to get into the field of archaeogenetics?
I would tell them “too late: the low-hanging fruit has been picked”.
If you are a young person and have the same fascination with immortality that I have, then study a verifiable discipline such as chemistry for 3 years. If as a sciences student you find out that you are a hard worker who spends the summer holidays in the laboratory, and are intellectually honest enough to be able to admit your own mistakes to yourself within 48 hours of making those mistakes, and if you experience that you can psychologically rebound from justified criticism by colleagues and superiors, then go into developing fields within historical linguistics, or medical genetics, and question their assumptions in the same way that Colin Renfrew or I have questioned received wisdom, and start from first principles to move the field forward.
Choose to work with multi-talented colleagues or superiors who are not experts in your own field at all – this keeps envy and competition at bay.
Do not look to any human, however learned, for the truth – the truth lies buried in your data, and cleaning up the data until the truth shines through is all up to you.
The Cambridge World Prehistory (2014) is out in Spring 2014, and is available to pre-order as a 3 book hardback set.