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Jambo, bonjour, zdravstvujtye, dayo: these are a few of the languages

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that I've spoken little bits of over the course of the last six weeks,

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as I've been to 17 countries I think I'm up to, on this crazy tour I've been doing,

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checking out various aspects of the project that we're doing.

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And I'm going to tell you a little bit about later on.

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And visiting some pretty incredible places,

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places like Mongolia, Cambodia, New Guinea, South Africa, Tanzania twice --

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I was here a month ago.

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And the opportunity to make a whirlwind tour of the world like that

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is utterly amazing, for lots of reasons.

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You see some incredible stuff.

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And you get to make these spot comparisons

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between people all around the globe.

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And the thing that you really take away from that,

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the kind of surface thing that you take away from it,

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is not that we're all one, although I'm going to tell you about that,

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but rather how different we are.

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There is so much diversity around the globe.

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6,000 different languages spoken by six and a half billion people,

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all different colors, shapes, sizes.

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You walk down the street in any big city, you travel like that,

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and you are amazed at the diversity in the human species.

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How do we explain that diversity?

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Well, that's what I'm going to talk about today,

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is how we're using the tools of genetics,

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population genetics in particular, to tell us how we generated this diversity,

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and how long it took.

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Now, the problem of human diversity,

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like all big scientific questions --

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how do you explain something like that --

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can be broken down into sub-questions.

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And you can ferret away at those little sub-questions.

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First one is really a question of origins.

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Do we all share a common origin, in fact?

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And given that we do -- and that's the assumption

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everybody, I think, in this room would make -- when was that?

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When did we originate as a species?

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How long have we been divergent from each other?

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And the second question is related, but slightly different.

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If we do spring from a common source,

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how did we come to occupy every corner of the globe,

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and in the process generate all of this diversity,

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the different ways of life, the different appearances,

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the different languages around the world?

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Well, the question of origins, as with so many other questions in biology,

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seems to have been answered by Darwin over a century ago.

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In "The Descent of Man," he wrote,

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"In each great region of the world, the living mammals

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are closely related to the extinct species of the same region.

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It's therefore probable that Africa was formerly inhabited by extinct apes

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closely allied to the gorilla and chimpanzee,

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and as these two species are now man's nearest allies,

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it's somewhat more probable that our early progenitors

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lived on the African continent than elsewhere."

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So we're done, we can go home -- finished the origin question.

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Well, not quite. Because Darwin was talking about our distant ancestry,

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our common ancestry with apes.

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And it is quite clear that apes originated on the African continent.

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Around 23 million years ago, they appear in the fossil record.

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Africa was actually disconnected from the other landmasses at that time,

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due to the vagaries of plate tectonics, floating around the Indian Ocean.

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Bumped into Eurasia around 16 million years ago,

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and then we had the first African exodus, as we call it.

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The apes that left at that time ended up in Southeast Asia,

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became the gibbons and the orangutans.

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And the ones that stayed on in Africa

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evolved into the gorillas, the chimpanzees and us.

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So, yes, if you're talking about our common ancestry with apes,

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it's very clear, by looking at the fossil record, we started off here.

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But that's not really the question I'm asking.

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I'm asking about our human ancestry,

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things that we would recognize as being like us

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if they were sitting here in the room.

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If they were peering over your shoulder,

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you wouldn't leap back, like that. What about our human ancestry?

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Because if we go far enough back,

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we share a common ancestry with every living thing on Earth.

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DNA ties us all together, so we share ancestry with barracuda

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and bacteria and mushrooms, if you go far enough back -- over a billion years.

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What we're asking about though is human ancestry.

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How do we study that?

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Well, historically, it has been studied using the science of paleoanthropology.

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Digging things up out of the ground,

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and largely on the basis of morphology --

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the way things are shaped, often skull shape -- saying,

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"This looks a little bit more like us than that, so this must be my ancestor.

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This must be who I'm directly descended from."

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The field of paleoanthropology, I'll argue,

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gives us lots of fascinating possibilities about our ancestry,

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but it doesn't give us the probabilities that we really want as scientists.

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What do I mean by that?

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You're looking at a great example here.

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These are three extinct species of hominids,

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potential human ancestors.

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All dug up just west of here in Olduvai Gorge, by the Leakey family.

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And they're all dating to roughly the same time.

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From left to right, we've got Homo erectus, Homo habilis,

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and Australopithecus -- now called Paranthropus boisei,

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the robust australopithecine. Three extinct species, same place, same time.

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That means that not all three could be my direct ancestor.

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Which one of these guys am I actually related to?

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Possibilities about our ancestry, but not the probabilities that we're really looking for.

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Well, a different approach has been to look at morphology in humans

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using the only data that people really had at hand until quite recently --

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again, largely skull shape.

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The first person to do this systematically was Linnaeus,

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Carl von Linne, a Swedish botanist,

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who in the eighteenth century took it upon himself

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to categorize every living organism on the planet.

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You think you've got a tough job?

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And he did a pretty good job.

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He categorized about 12,000 species in "Systema Naturae."

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He actually coined the term Homo sapiens -- it means wise man in Latin.

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But looking around the world at the diversity of humans, he said,

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"Well, you know, we seem to come in discreet sub-species or categories."

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And he talked about Africans and Americans and Asians and Europeans,

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and a blatantly racist category he termed "Monstrosus,"

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which basically included all the people he didn't like,

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including imaginary folk like elves.

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It's easy to dismiss this as the perhaps well-intentioned

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but ultimately benighted musings of an eighteenth century scientist

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working in the pre-Darwinian era.

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Except, if you had taken physical anthropology

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as recently as 20 or 30 years ago, in many cases you would have learned

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basically that same classification of humanity.

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Human races that according to physical anthropologists of 30, 40 years ago --

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Carlton Coon is the best example --

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had been diverging from each other -- this was in the post-Darwinian era --

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for over a million years, since the time of Homo erectus.

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But based on what data?

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Very little. Very little. Morphology and a lot of guesswork.

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Well, what I'm going to talk about today,

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what I'm going to talk about now is a new approach to this problem.

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Instead of going out and guessing about our ancestry,

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digging things up out of the ground, possible ancestors,

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and saying it on the basis of morphology --

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which we still don't completely understand,

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we don't know the genetic causes underlying this morphological variation --

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what we need to do is turn the problem on its head.

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Because what we're really asking is a genealogical problem,

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or a genealogical question.

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What we're trying to do is construct a family tree for everybody alive today.

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And as any genealogist will tell you --

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anybody have a member of the family, or maybe you

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have tried to construct a family tree, trace back in time?

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You start in the present, with relationships you're certain about.

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You and your siblings, you have a parent in common.

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You and your cousins share a grandparent in common.

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You gradually trace further and further back into the past,

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adding these ever more distant relationships.

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But eventually, no matter how good you are at digging up the church records,

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and all that stuff, you hit what the genealogists call a brick wall.

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A point beyond which you don't know anything else about your ancestors,

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and you enter this dark and mysterious realm we call history

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that we have to feel our way through with whispered guidance.

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Who were these people who came before?

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We have no written record. Well, actually, we do.

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Written in our DNA, in our genetic code --

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we have a historical document that takes us back in time

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to the very earliest days of our species. And that's what we study.

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Now, a quick primer on DNA.

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I suspect that not everybody in the audience is a geneticist.

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It is a very long, linear molecule, a coded version

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of how to make another copy of you. It's your blueprint.

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It's composed of four subunits: A, C, G and T, we call them.

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And it's the sequence of those subunits that defines that blueprint.

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How long is it? Well, it's billions of these subunits in length.

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A haploid genome -- we actually have two copies of all of our chromosomes --

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a haploid genome is around 3.2 billion nucleotides in length.

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And the whole thing, if you add it all together,

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is over six billion nucleotides long.

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If you take all the DNA out of one cell in your body,

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and stretch it end to end, it's around two meters long.

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If you take all the DNA out of every cell in your body,

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and you stretch it end to end, it would reach from here to the moon and back,

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thousands of times. It's a lot of information.

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And so when you're copying this DNA molecule to pass it on, it's a pretty tough job.

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Imagine the longest book you can think of, "War and Peace."

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Now multiply it by 100.

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And imagine copying that by hand.

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And you're working away until late at night,

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and you're very, very careful, and you're drinking coffee

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and you're paying attention, but, occasionally,

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when you're copying this by hand,

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you're going to make a little typo, a spelling mistake --

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substitute an I for an E, or a C for a T.

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Same thing happens to our DNA as it's being passed on through the generations.

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It doesn't happen very often. We have a proofreading mechanism built in.

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But when it does happen, and these changes get transmitted down

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through the generations, they become markers of descent.

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If you share a marker with someone,

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it means you share an ancestor at some point in the past,

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the person who first had that change in their DNA.

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And it's by looking at the pattern of genetic variation,

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the pattern of these markers in people all over the world,

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and assessing the relative ages when they occurred throughout our history,

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that we've been able to construct a family tree for everybody alive today.

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These are two pieces of DNA that we use quite widely in our work.

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Mitochondrial DNA, tracing a purely maternal line of descent.

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You get your mtDNA from your mother, and your mother's mother,

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all the way back to the very first woman.

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The Y chromosome, the piece of DNA that makes men men,

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traces a purely paternal line of descent.

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Everybody in this room, everybody in the world,

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falls into a lineage somewhere on these trees.

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Now, even though these are simplified versions of the real trees,

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they're still kind of complicated, so let's simplify them.

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Turn them on their sides, combine them so that they look like a tree

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with the root at the bottom and the branches going up.

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What's the take-home message?

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Well, the thing that jumps out at you first

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is that the deepest lineages in our family trees

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are found within Africa, among Africans.

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That means that Africans have been accumulating

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this mutational diversity for longer.

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And what that means is that we originated in Africa. It's written in our DNA.

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Every piece of DNA we look at has greater diversity within Africa than outside of Africa.

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And at some point in the past, a sub-group of Africans

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left the African continent to go out and populate the rest of the world.

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Now, how recently do we share this ancestry?

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Was it millions of years ago, which we might suspect

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by looking at all this incredible variation around the world?

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No, the DNA tells a story that's very clear.

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Within the last 200,000 years, we all share an ancestor, a single person --

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Mitochondrial Eve, you might have heard about her -- in Africa,

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an African woman who gave rise to all the mitochondrial diversity in the world today.

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But what's even more amazing

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is that if you look at the Y-chromosome side,

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the male side of the story, the Y-chromosome Adam

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only lived around 60,000 years ago.

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That's only about 2,000 human generations,

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the blink of an eye in an evolutionary sense.

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That tells us we were all still living in Africa at that time.

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This was an African man who gave rise

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to all the Y chromosome diversity around the world.

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It's only within the last 60,000 years

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that we have started to generate this incredible diversity we see around the world.

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Such an amazing story.

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We're all effectively part of an extended African family.

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Now, that seems so recent. Why didn't we start to leave earlier?

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Why didn't Homo erectus evolve into separate species,

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or sub-species rather, human races around the world?

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Why was it that we seem to have come out of Africa so recently?

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Well, that's a big question. These "why" questions,

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particularly in genetics and the study of history in general, are always the big ones,

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the ones that are tough to answer.

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And so when all else fails, talk about the weather.

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What was going on to the world's weather around 60,000 years ago?

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Well, we were going into the worst part of the last ice age.

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The last ice age started roughly 120,000 years ago.

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It went up and down, and it really started to accelerate around 70,000 years ago.

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Lots of evidence from sediment cores

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and the pollen types, oxygen isotopes and so on.

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We hit the last glacial maximum around 16,000 years ago,

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but basically, from 70,000 years on, things were getting really tough,

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getting very cold. The Northern Hemisphere had massive growing ice sheets.

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New York City, Chicago, Seattle, all under a sheet of ice.

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Most of Britain, all of Scandinavia, covered by ice several kilometers thick.

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Now, Africa is the most tropical continent on the planet --

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about 85 percent of it lies between Cancer and Capricorn --

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and there aren't a lot of glaciers here,

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except on the high mountains here in East Africa.

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So what was going on here? We weren't covered in ice in Africa.

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Rather, Africa was drying out at that time.

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This is a paleo-climatological map

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of what Africa looked like between 60,000 and 70,000 years ago,

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reconstructed from all these pieces of evidence that I mentioned before.

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The reason for that is that ice actually sucks moisture out of the atmosphere.

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If you think about Antarctica, it's technically a desert, it gets so little precipitation.

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So the whole world was drying out.

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The sea levels were dropping. And Africa was turning to desert.

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The Sahara was much bigger then than it is now.

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And the human habitat was reduced to just a few small pockets,

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compared to what we have today.

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The evidence from genetic data

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is that the human population around this time, roughly 70,000 years ago,

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crashed to fewer than 2,000 individuals.

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We nearly went extinct. We were hanging on by our fingernails.

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And then something happened. A great illustration of it.

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Look at some stone tools.

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The ones on the left are from Africa, from around a million years ago.

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The ones on the right were made by Neanderthals, our distant cousins,

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not our direct ancestors, living in Europe,

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and they date from around 50,000 or 60,000 years ago.

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Now, at the risk of offending any paleoanthropologists

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or physical anthropologists in the audience,

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basically there's not a lot of change between these two stone tool groups.

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The ones on the left are pretty similar to the ones on the right.

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We are in a period of long cultural stasis from a million years ago

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until around 60,000 to 70,000 years ago.

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The tool styles don't change that much.

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The evidence is that the human way of life

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didn't change that much during that period.

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But then 50, 60, 70 thousand years ago, somewhere in that region,

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all hell breaks loose. Art makes its appearance.

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The stone tools become much more finely crafted.

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The evidence is that humans begin to specialize in particular prey species,

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at particular times of the year.

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The population size started to expand.

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Probably, according to what many linguists believe,

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fully modern language, syntactic language -- subject, verb, object --

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that we use to convey complex ideas, like I'm doing now, appeared around that time.

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We became much more social. The social networks expanded.

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This change in behavior allowed us to survive these worsening conditions in Africa,

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and they allowed us to start to expand around the world.

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We've been talking at this conference about African success stories.

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Well, you want the ultimate African success story?

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Look in the mirror. You're it. The reason you're alive today

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is because of those changes in our brains that took place in Africa --

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probably somewhere in the region where we're sitting right now,

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around 60, 70 thousand years ago --

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allowing us not only to survive in Africa, but to expand out of Africa.

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An early coastal migration along the south coast of Asia,

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leaving Africa around 60,000 years ago,

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reaching Australia very rapidly, by 50,000 years ago.

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A slightly later migration up into the Middle East.

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These would have been savannah hunters.

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So those of you who are going on one of the post-conference tours,

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you'll get to see what a real savannah is like.

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And it's basically a meat locker.

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People who would have specialized in killing the animals,

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hunting the animals on those meat locker savannahs, moving up,

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following the grasslands into the Middle East around 45,000 years ago,

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during one of the rare wet phases in the Sahara.

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Migrating eastward, following the grasslands,

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because that's what they were adapted to live on.

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And when they reached Central Asia,

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they reached what was effectively a steppe super-highway,

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a grassland super-highway.

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The grasslands at that time -- this was during the last ice age --

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stretched basically from Germany all the way over to Korea,

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and the entire continent was open to them.

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Entering Europe around 35,000 years ago,

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and finally, a small group migrating up

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through the worst weather imaginable, Siberia,

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inside the Arctic Circle, during the last ice age --

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temperature was at -70, -80, even -100, perhaps --

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migrating into the Americas, ultimately reaching that final frontier.

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An amazing story, and it happened first in Africa.

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The changes that allowed us to do that,

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the evolution of this highly adaptable brain that we all carry around with us,

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allowing us to create novel cultures,

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allowing us to develop the diversity

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that we see on a whirlwind trip like the one I've just been on.

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Now, that story I just told you is literally a whirlwind tour

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of how we populated the world, the great Paleolithic wanderings of our species.

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And that's the story that I told a couple of years ago

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in my book, "The Journey of Man," and a film that we made with the same title.

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And as we were finishing up that film --

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it was co-produced with National Geographic --

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I started talking to the folks at NG about this work.

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And they got really excited about it. They liked the film, but they said,

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"You know, we really see this as kind of

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the next wave in the study of human origins, where we all came from,

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using the tools of DNA to map the migrations around the world.

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You know, the study of human origins is kind of in our DNA,

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and we want to take it to the next level.

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What do you want to do next?"

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Which is a great question to be asked by National Geographic.

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And I said, "Well, you know, what I've sketched out here is just that.

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It is a very coarse sketch of how we migrated around the planet.

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And it's based on a few thousand people we've sampled from,

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you know, a handful of populations around the world.

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Studied a few genetic markers, and there are lots of gaps on this map.

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We've just connected the dots. What we need to do

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is increase our sample size by an order of magnitude or more --

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hundreds of thousands of DNA samples from people all over the world."

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And that was the genesis of the Genographic Project.

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The project launched in April 2005.

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It has three core components. Obviously, science is a big part of it.

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The field research that we're doing around the world with indigenous peoples.

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People who have lived in the same location for a long period of time

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retain a connection to the place where they live

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that many of the rest of us have lost.

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So my ancestors come from all over northern Europe.

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I live in the Eastern Seaboard of North America when I'm not traveling.

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Where am I indigenous to? Nowhere really. My genes are all jumbled up.

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But there are people who retain that link to their ancestors

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that allows us to contextualize the DNA results.

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That's the focus of the field research,

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the centers that we've set up all over the world --

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10 of them, top population geneticists.

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But, in addition, we wanted to open up this study to anybody around the world.

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How often do you get to participate in a big scientific project?

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The Human Genome Project, or a Mars Rover mission.

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In this case, you actually can.

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You can go onto our website, Nationalgeographic.com/genographic.

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You can order a kit. You can test your own DNA.

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And you can actually submit those results to the database,

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and tell us a little about your genealogical background,

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have the data analyzed as part of the scientific effort.

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Now, this is all a nonprofit enterprise, and so the money that we raise,

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after we cover the cost of doing the testing and making the kit components,

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gets plowed back into the project.

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The majority going to something we call the Legacy Fund.

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It's a charitable entity, basically a grant-giving entity

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that gives money back to indigenous groups around the world

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for educational, cultural projects initiated by them.

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They apply to this fund in order to do various projects,

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and I'll show you a couple of examples.

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So how are we doing on the project? We've got about 25,000 samples

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collected from indigenous people around the world.

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The most amazing thing has been the interest on the part of the public;

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210,000 people have ordered these participation kits

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since we launched two years ago,

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which has raised around five million dollars,

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the majority of which, at least half, is going back into the Legacy Fund.

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We've just awarded the first Legacy Grants totaling around 500,000 dollars.

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Projects around the world -- documenting oral poetry in Sierra Leone,

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preserving traditional weaving patterns in Gaza,

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language revitalization in Tajikistan, etc., etc.

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So the project is going very, very well,

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and I urge you to check out the website and watch this space.

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Thank you very much.

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(Applause)