Dr. Spencer Wells on the Genographic Project's First Results

Description: Back from the verge of extinction.

Question: What conclusions have you been able to gather from the data so far?

Transcript: Probably the coolest thing to come out of the genetic results is how small the human population probably was.  If you go back to around 70 to 80,000 years ago, we were very nearly extinct, probably the total number of people living in the world at that time and again we were still all living in Africa could have fit into a small symphony hall, around 2000 people, maybe even less and so we nearly went extinct and this was probably due to climate shifts that were occurring around that time.  We were in the midst of the last ice age, things really started to get bad between 70 and 80,000 years ago. There was a massive volcanic eruption in Sumatra that is Mt. Toba that erupted around 74,000 years ago.  The combination of these factors probably drove the human population very close to extinction and we came back from that and we figured out a way to survive these horrible climatic conditions and that probably primed the pump if you will to allow us to go out and explore the rest of the world and actually make proper forays into the part of Asia, off into Europe, South East Asia, Australia and ultimately into the Americas between 15 and 20,000 years ago.  So the evidence is that we started to leave between 50 and 60,000 years ago following a coastal route along the south coast of Asia, beach combing our way along, living on, you know, marine resources, shellfish, probably doing a little bit of fish trapping.  We rapidly made it down to South East Asia to Australia by around 50,000 years ago when humans show up in the fossil record there.  There was a later migration between 45 and 50,000 years ago according to our data that came via an inland route, cross the Sahara at a point when the Sahara was actually a very nice place to live.  Every 20,000 years or so due to fluctuations, the way the earth precesses in its orbit, the way it rotates and this causes shifts in the way the monsoon rains fall in Africa.  Every 20,000 years or so the Sahara’s actually a pretty nice place and it was an extension of the grasslands of East Africa around 50,000 years ago and this allowed people to slowly move up into northern Africa, out into the middle east and that led them on their way to the rest of the world.  So it’s really kind of these grand sweeping Paleolithic migratory routes that we’re following but also very specific details, I mean all the way up to the present day nearly, historical events.  We published a paper about a month ago in the American Journal of Human Genetics showing that the Christian population of Lebanon is carrying genetic markers that tie them to the crusaders from Western Europe who came over only about 800, 900 years ago and so these are events that we knew about from the historical record, hadn’t seen a genetic trail, prior to this because we didn’t have enough samples but now we’re seeing it, you know, as we increase the sample size; everything from the very earliest days of our species up to very recent events.

Question: How do you know where a group of people was 35,000 years ago?

Transcript: Okay what underpins the work we’re doing, the scientific work is the idea that DNA changes over time at a regular rate, so DNA is a very long linear molecule, it’s a coded molecule, there are 4 sub units, so think of it as Morse code but with 4 different possibilities rather than just dots and dashes and it’s the sequence of these sub units that is basically a blue print to make another version of you and if you choose to have kids, as your parents did, you have to copy this very long molecule or document to pass it onto them and when you’re copying it, because it is so very long, there are billions of these sub units, occasionally you’re gonna make a mistake, a typo.  So imagine copying the longest text you can think of, War and Peace but multiply it by a hundred and you’re copying it by hand, staying up late at night and you’re very, very careful but occasionally you’re gonna make a typo, substitute and I for an E or in the case of DNA, a C for G or an A for a T.  These don’t happen very often at the genetic level, they’re called mutations, when they do occur and they occur at a rate of around 50 per genome per generation.  So not very often, 50 out of the billions of sub units we have.  But when they happen and they get passed on through the generations, they become markers of descent and that’s how we place people into these lineages.  So again if you share one of these markers with someone, you share an ancestor, the person who first had that change in their DNA.  Now because we know the rate at which they occur, by looking at the number of changes that have accumulated on a lineage, we can estimate the age of that lineage and by comparing the distribution of the lineage to populations all over the world, seeing which population’s it’s found in, in which population’s it’s not found in.  Indigenous groups, people who’ve lived in the same place for a long period of time give us an insight into their ancestor’s genetic patterns.  By looking at the distribution in those groups all over the world we can actually map where it originated and how it spread around the planet.

Recorded on: 5/22/08