WEBVTT 00:00:00.000 --> 00:00:03.000 What I want to talk to you about 00:00:03.000 --> 00:00:05.000 is what we can learn from studying the genomes 00:00:05.000 --> 00:00:07.000 of living people 00:00:07.000 --> 00:00:09.000 and extinct humans. 00:00:09.000 --> 00:00:11.000 But before doing that, 00:00:11.000 --> 00:00:14.000 I just briefly want to remind you about what you already know: 00:00:14.000 --> 00:00:16.000 that our genomes, our genetic material, 00:00:16.000 --> 00:00:19.000 are stored in almost all cells in our bodies in chromosomes 00:00:19.000 --> 00:00:21.000 in the form of DNA, 00:00:21.000 --> 00:00:24.000 which is this famous double-helical molecule. 00:00:24.000 --> 00:00:26.000 And the genetic information 00:00:26.000 --> 00:00:28.000 is contained in the form of a sequence 00:00:28.000 --> 00:00:30.000 of four bases 00:00:30.000 --> 00:00:33.000 abbreviated with the letters A, T, C and G. 00:00:33.000 --> 00:00:35.000 And the information is there twice -- 00:00:35.000 --> 00:00:37.000 one on each strand -- 00:00:37.000 --> 00:00:39.000 which is important, 00:00:39.000 --> 00:00:41.000 because when new cells are formed, these strands come apart, 00:00:41.000 --> 00:00:44.000 new strands are synthesized with the old ones as templates 00:00:44.000 --> 00:00:47.000 in an almost perfect process. NOTE Paragraph 00:00:47.000 --> 00:00:49.000 But nothing, of course, in nature 00:00:49.000 --> 00:00:51.000 is totally perfect, 00:00:51.000 --> 00:00:53.000 so sometimes an error is made 00:00:53.000 --> 00:00:56.000 and a wrong letter is built in. 00:00:56.000 --> 00:00:58.000 And we can then see the result 00:00:58.000 --> 00:01:00.000 of such mutations 00:01:00.000 --> 00:01:02.000 when we compare DNA sequences 00:01:02.000 --> 00:01:05.000 among us here in the room, for example. 00:01:05.000 --> 00:01:08.000 If we compare my genome to the genome of you, 00:01:08.000 --> 00:01:12.000 approximately every 1,200, 1,300 letters 00:01:12.000 --> 00:01:14.000 will differ between us. 00:01:14.000 --> 00:01:16.000 And these mutations accumulate 00:01:16.000 --> 00:01:19.000 approximately as a function of time. 00:01:19.000 --> 00:01:22.000 So if we add in a chimpanzee here, we will see more differences. 00:01:22.000 --> 00:01:25.000 Approximately one letter in a hundred 00:01:25.000 --> 00:01:27.000 will differ from a chimpanzee. NOTE Paragraph 00:01:27.000 --> 00:01:29.000 And if you're then interested in the history 00:01:29.000 --> 00:01:31.000 of a piece of DNA, or the whole genome, 00:01:31.000 --> 00:01:34.000 you can reconstruct the history of the DNA 00:01:34.000 --> 00:01:36.000 with those differences you observe. 00:01:36.000 --> 00:01:40.000 And generally we depict our ideas about this history 00:01:40.000 --> 00:01:42.000 in the form of trees like this. 00:01:42.000 --> 00:01:44.000 In this case, it's very simple. 00:01:44.000 --> 00:01:46.000 The two human DNA sequences 00:01:46.000 --> 00:01:49.000 go back to a common ancestor quite recently. 00:01:49.000 --> 00:01:53.000 Farther back is there one shared with chimpanzees. 00:01:53.000 --> 00:01:56.000 And because these mutations 00:01:56.000 --> 00:01:58.000 happen approximately as a function of time, 00:01:58.000 --> 00:02:00.000 you can transform these differences 00:02:00.000 --> 00:02:02.000 to estimates of time, 00:02:02.000 --> 00:02:04.000 where the two humans, typically, 00:02:04.000 --> 00:02:08.000 will share a common ancestor about half a million years ago, 00:02:08.000 --> 00:02:10.000 and with the chimpanzees, 00:02:10.000 --> 00:02:13.000 it will be in the order of five million years ago. NOTE Paragraph 00:02:13.000 --> 00:02:15.000 So what has now happened in the last few years 00:02:15.000 --> 00:02:17.000 is that there are account technologies around 00:02:17.000 --> 00:02:21.000 that allow you to see many, many pieces of DNA very quickly. 00:02:21.000 --> 00:02:23.000 So we can now, in a matter of hours, 00:02:23.000 --> 00:02:26.000 determine a whole human genome. 00:02:26.000 --> 00:02:29.000 Each of us, of course, contains two human genomes -- 00:02:29.000 --> 00:02:32.000 one from our mothers and one from our fathers. 00:02:32.000 --> 00:02:36.000 And they are around three billion such letters long. 00:02:36.000 --> 00:02:38.000 And we will find that the two genomes in me, 00:02:38.000 --> 00:02:40.000 or one genome of mine we want to use, 00:02:40.000 --> 00:02:43.000 will have about three million differences 00:02:43.000 --> 00:02:45.000 in the order of that. 00:02:45.000 --> 00:02:47.000 And what you can then also begin to do 00:02:47.000 --> 00:02:49.000 is to say, "How are these genetic differences 00:02:49.000 --> 00:02:51.000 distributed across the world?" 00:02:51.000 --> 00:02:53.000 And if you do that, 00:02:53.000 --> 00:02:57.000 you find a certain amount of genetic variation in Africa. 00:02:57.000 --> 00:03:00.000 And if you look outside Africa, 00:03:00.000 --> 00:03:03.000 you actually find less genetic variation. 00:03:03.000 --> 00:03:05.000 This is surprising, of course, 00:03:05.000 --> 00:03:08.000 because in the order of six to eight times fewer people 00:03:08.000 --> 00:03:11.000 live in Africa than outside Africa. 00:03:11.000 --> 00:03:14.000 Yet the people inside Africa 00:03:14.000 --> 00:03:17.000 have more genetic variation. NOTE Paragraph 00:03:17.000 --> 00:03:19.000 Moreover, almost all these genetic variants 00:03:19.000 --> 00:03:21.000 we see outside Africa 00:03:21.000 --> 00:03:23.000 have closely related DNA sequences 00:03:23.000 --> 00:03:25.000 that you find inside Africa. 00:03:25.000 --> 00:03:27.000 But if you look in Africa, 00:03:27.000 --> 00:03:30.000 there is a component of the genetic variation 00:03:30.000 --> 00:03:33.000 that has no close relatives outside. 00:03:33.000 --> 00:03:36.000 So a model to explain this 00:03:36.000 --> 00:03:39.000 is that a part of the African variation, but not all of it, 00:03:39.000 --> 00:03:43.000 [has] gone out and colonized the rest of the world. 00:03:43.000 --> 00:03:47.000 And together with the methods to date these genetic differences, 00:03:47.000 --> 00:03:49.000 this has led to the insight 00:03:49.000 --> 00:03:51.000 that modern humans -- 00:03:51.000 --> 00:03:54.000 humans that are essentially indistinguishable from you and me -- 00:03:54.000 --> 00:03:57.000 evolved in Africa, quite recently, 00:03:57.000 --> 00:04:01.000 between 100 and 200,000 years ago. 00:04:01.000 --> 00:04:05.000 And later, between 100 and 50,000 years ago or so, 00:04:05.000 --> 00:04:07.000 went out of Africa 00:04:07.000 --> 00:04:09.000 to colonize the rest of the world. NOTE Paragraph 00:04:09.000 --> 00:04:11.000 So what I often like to say 00:04:11.000 --> 00:04:13.000 is that, from a genomic perspective, 00:04:13.000 --> 00:04:15.000 we are all Africans. 00:04:15.000 --> 00:04:18.000 We either live inside Africa today, 00:04:18.000 --> 00:04:20.000 or in quite recent exile. 00:04:20.000 --> 00:04:22.000 Another consequence 00:04:22.000 --> 00:04:25.000 of this recent origin of modern humans 00:04:25.000 --> 00:04:27.000 is that genetic variants 00:04:27.000 --> 00:04:29.000 are generally distributed widely in the world, 00:04:29.000 --> 00:04:31.000 in many places, 00:04:31.000 --> 00:04:34.000 and they tend to vary as gradients, 00:04:34.000 --> 00:04:38.000 from a bird's-eye perspective at least. 00:04:38.000 --> 00:04:40.000 And since there are many genetic variants, 00:04:40.000 --> 00:04:43.000 and they have different such gradients, 00:04:43.000 --> 00:04:46.000 this means that if we determine a DNA sequence -- 00:04:46.000 --> 00:04:49.000 a genome from one individual -- 00:04:49.000 --> 00:04:51.000 we can quite accurately estimate 00:04:51.000 --> 00:04:53.000 where that person comes from, 00:04:53.000 --> 00:04:55.000 provided that its parents or grandparents 00:04:55.000 --> 00:04:58.000 haven't moved around too much. NOTE Paragraph 00:04:58.000 --> 00:05:00.000 But does this then mean, 00:05:00.000 --> 00:05:02.000 as many people tend to think, 00:05:02.000 --> 00:05:05.000 that there are huge genetic differences between groups of people -- 00:05:05.000 --> 00:05:07.000 on different continents, for example? 00:05:07.000 --> 00:05:10.000 Well we can begin to ask those questions also. 00:05:10.000 --> 00:05:13.000 There is, for example, a project that's underway 00:05:13.000 --> 00:05:15.000 to sequence a thousand individuals -- 00:05:15.000 --> 00:05:18.000 their genomes -- from different parts of the world. 00:05:18.000 --> 00:05:21.000 They've sequenced 185 Africans 00:05:21.000 --> 00:05:24.000 from two populations in Africa. 00:05:24.000 --> 00:05:27.000 [They've] sequenced approximately equally [as] many people 00:05:27.000 --> 00:05:30.000 in Europe and in China. 00:05:30.000 --> 00:05:33.000 And we can begin to say how much variance do we find, 00:05:33.000 --> 00:05:36.000 how many letters that vary 00:05:36.000 --> 00:05:39.000 in at least one of those individual sequences. 00:05:39.000 --> 00:05:43.000 And it's a lot: 38 million variable positions. NOTE Paragraph 00:05:43.000 --> 00:05:46.000 But we can then ask: Are there any absolute differences 00:05:46.000 --> 00:05:48.000 between Africans and non-Africans? 00:05:48.000 --> 00:05:50.000 Perhaps the biggest difference 00:05:50.000 --> 00:05:52.000 most of us would imagine existed. 00:05:52.000 --> 00:05:54.000 And with absolute difference -- 00:05:54.000 --> 00:05:56.000 and I mean a difference 00:05:56.000 --> 00:05:59.000 where people inside Africa at a certain position, 00:05:59.000 --> 00:06:02.000 where all individuals -- 100 percent -- have one letter, 00:06:02.000 --> 00:06:06.000 and everybody outside Africa has another letter. 00:06:06.000 --> 00:06:09.000 And the answer to that, among those millions of differences, 00:06:09.000 --> 00:06:12.000 is that there is not a single such position. 00:06:14.000 --> 00:06:16.000 This may be surprising. 00:06:16.000 --> 00:06:19.000 Maybe a single individual is misclassified or so. 00:06:19.000 --> 00:06:21.000 So we can relax the criterion a bit 00:06:21.000 --> 00:06:23.000 and say: How many positions do we find 00:06:23.000 --> 00:06:25.000 where 95 percent of people in Africa have 00:06:25.000 --> 00:06:27.000 one variant, 00:06:27.000 --> 00:06:29.000 95 percent another variant, 00:06:29.000 --> 00:06:31.000 and the number of that is 12. NOTE Paragraph 00:06:31.000 --> 00:06:33.000 So this is very surprising. 00:06:33.000 --> 00:06:35.000 It means that when we look at people 00:06:35.000 --> 00:06:38.000 and see a person from Africa 00:06:38.000 --> 00:06:41.000 and a person from Europe or Asia, 00:06:41.000 --> 00:06:45.000 we cannot, for a single position in the genome with 100 percent accuracy, 00:06:45.000 --> 00:06:47.000 predict what the person would carry. 00:06:47.000 --> 00:06:49.000 And only for 12 positions 00:06:49.000 --> 00:06:53.000 can we hope to be 95 percent right. 00:06:53.000 --> 00:06:55.000 This may be surprising, 00:06:55.000 --> 00:06:57.000 because we can, of course, look at these people 00:06:57.000 --> 00:07:01.000 and quite easily say where they or their ancestors came from. 00:07:01.000 --> 00:07:03.000 So what this means now 00:07:03.000 --> 00:07:05.000 is that those traits we then look at 00:07:05.000 --> 00:07:07.000 and so readily see -- 00:07:07.000 --> 00:07:10.000 facial features, skin color, hair structure -- 00:07:10.000 --> 00:07:14.000 are not determined by single genes with big effects, 00:07:14.000 --> 00:07:17.000 but are determined by many different genetic variants 00:07:17.000 --> 00:07:19.000 that seem to vary in frequency 00:07:19.000 --> 00:07:21.000 between different parts of the world. NOTE Paragraph 00:07:21.000 --> 00:07:24.000 There is another thing with those traits 00:07:24.000 --> 00:07:27.000 that we so easily observe in each other 00:07:27.000 --> 00:07:29.000 that I think is worthwhile to consider, 00:07:29.000 --> 00:07:32.000 and that is that, in a very literal sense, 00:07:32.000 --> 00:07:35.000 they're really on the surface of our bodies. 00:07:35.000 --> 00:07:37.000 They are what we just said -- 00:07:37.000 --> 00:07:40.000 facial features, hair structure, skin color. 00:07:40.000 --> 00:07:42.000 There are also a number of features 00:07:42.000 --> 00:07:44.000 that vary between continents like that 00:07:44.000 --> 00:07:48.000 that have to do with how we metabolize food that we ingest, 00:07:48.000 --> 00:07:50.000 or that have to do 00:07:50.000 --> 00:07:53.000 with how our immune systems deal with microbes 00:07:53.000 --> 00:07:55.000 that try to invade our bodies. 00:07:55.000 --> 00:07:57.000 But so those are all parts of our bodies 00:07:57.000 --> 00:08:00.000 where we very directly interact with our environment, 00:08:00.000 --> 00:08:04.000 in a direct confrontation, if you like. 00:08:04.000 --> 00:08:06.000 It's easy to imagine 00:08:06.000 --> 00:08:08.000 how particularly those parts of our bodies 00:08:08.000 --> 00:08:11.000 were quickly influenced by selection from the environment 00:08:11.000 --> 00:08:13.000 and shifted frequencies of genes 00:08:13.000 --> 00:08:15.000 that are involved in them. 00:08:15.000 --> 00:08:18.000 But if we look on other parts of our bodies 00:08:18.000 --> 00:08:20.000 where we don't directly interact with the environment -- 00:08:20.000 --> 00:08:23.000 our kidneys, our livers, our hearts -- 00:08:23.000 --> 00:08:25.000 there is no way to say, 00:08:25.000 --> 00:08:27.000 by just looking at these organs, 00:08:27.000 --> 00:08:30.000 where in the world they would come from. NOTE Paragraph 00:08:31.000 --> 00:08:33.000 So there's another interesting thing 00:08:33.000 --> 00:08:36.000 that comes from this realization 00:08:36.000 --> 00:08:40.000 that humans have a recent common origin in Africa, 00:08:40.000 --> 00:08:43.000 and that is that when those humans emerged 00:08:43.000 --> 00:08:45.000 around 100,000 years ago or so, 00:08:45.000 --> 00:08:47.000 they were not alone on the planet. 00:08:47.000 --> 00:08:50.000 There were other forms of humans around, 00:08:50.000 --> 00:08:53.000 most famously perhaps, Neanderthals -- 00:08:53.000 --> 00:08:55.000 these robust forms of humans, 00:08:55.000 --> 00:08:57.000 compared to the left here 00:08:57.000 --> 00:09:01.000 with a modern human skeleton on the right -- 00:09:01.000 --> 00:09:04.000 that existed in Western Asia and Europe 00:09:04.000 --> 00:09:06.000 since several hundreds of thousands of years. 00:09:06.000 --> 00:09:08.000 So an interesting question is, 00:09:08.000 --> 00:09:10.000 what happened when we met? 00:09:10.000 --> 00:09:12.000 What happened to the Neanderthals? NOTE Paragraph 00:09:12.000 --> 00:09:14.000 And to begin to answer such questions, 00:09:14.000 --> 00:09:18.000 my research group -- since over 25 years now -- 00:09:18.000 --> 00:09:20.000 works on methods to extract DNA 00:09:20.000 --> 00:09:22.000 from remains of Neanderthals 00:09:22.000 --> 00:09:24.000 and extinct animals 00:09:24.000 --> 00:09:27.000 that are tens of thousands of years old. 00:09:27.000 --> 00:09:30.000 So this involves a lot of technical issues 00:09:30.000 --> 00:09:32.000 in how you extract the DNA, 00:09:32.000 --> 00:09:35.000 how you convert it to a form you can sequence. 00:09:35.000 --> 00:09:37.000 You have to work very carefully 00:09:37.000 --> 00:09:40.000 to avoid contamination of experiments 00:09:40.000 --> 00:09:43.000 with DNA from yourself. 00:09:43.000 --> 00:09:46.000 And this then, in conjunction with these methods 00:09:46.000 --> 00:09:50.000 that allow very many DNA molecules to be sequenced very rapidly, 00:09:50.000 --> 00:09:52.000 allowed us last year 00:09:52.000 --> 00:09:55.000 to present the first version of the Neanderthal genome, 00:09:55.000 --> 00:09:57.000 so that any one of you 00:09:57.000 --> 00:09:59.000 can now look on the Internet, on the Neanderthal genome, 00:09:59.000 --> 00:10:02.000 or at least on the 55 percent of it 00:10:02.000 --> 00:10:05.000 that we've been able to reconstruct so far. 00:10:05.000 --> 00:10:07.000 And you can begin to compare it to the genomes 00:10:07.000 --> 00:10:10.000 of people who live today. NOTE Paragraph 00:10:10.000 --> 00:10:12.000 And one question 00:10:12.000 --> 00:10:14.000 that you may then want to ask 00:10:14.000 --> 00:10:16.000 is, what happened when we met? 00:10:16.000 --> 00:10:18.000 Did we mix or not? 00:10:18.000 --> 00:10:20.000 And the way to ask that question 00:10:20.000 --> 00:10:23.000 is to look at the Neanderthal that comes from Southern Europe 00:10:23.000 --> 00:10:25.000 and compare it to genomes 00:10:25.000 --> 00:10:27.000 of people who live today. 00:10:27.000 --> 00:10:29.000 So we then look 00:10:29.000 --> 00:10:31.000 to do this with pairs of individuals, 00:10:31.000 --> 00:10:33.000 starting with two Africans, 00:10:33.000 --> 00:10:35.000 looking at the two African genomes, 00:10:35.000 --> 00:10:38.000 finding places where they differ from each other, 00:10:38.000 --> 00:10:41.000 and in each case ask: What is a Neanderthal like? 00:10:41.000 --> 00:10:44.000 Does it match one African or the other African? 00:10:44.000 --> 00:10:47.000 We would expect there to be no difference, 00:10:47.000 --> 00:10:49.000 because Neanderthals were never in Africa. 00:10:49.000 --> 00:10:52.000 They should be equal, have no reason to be closer 00:10:52.000 --> 00:10:55.000 to one African than another African. 00:10:55.000 --> 00:10:57.000 And that's indeed the case. 00:10:57.000 --> 00:10:59.000 Statistically speaking, there is no difference 00:10:59.000 --> 00:11:03.000 in how often the Neanderthal matches one African or the other. 00:11:03.000 --> 00:11:05.000 But this is different 00:11:05.000 --> 00:11:09.000 if we now look at the European individual and an African. 00:11:09.000 --> 00:11:12.000 Then, significantly more often, 00:11:12.000 --> 00:11:14.000 does a Neanderthal match the European 00:11:14.000 --> 00:11:16.000 rather than the African. 00:11:16.000 --> 00:11:19.000 The same is true if we look at a Chinese individual 00:11:19.000 --> 00:11:21.000 versus an African, 00:11:21.000 --> 00:11:25.000 the Neanderthal will match the Chinese individual more often. 00:11:25.000 --> 00:11:27.000 This may also be surprising 00:11:27.000 --> 00:11:29.000 because the Neanderthals were never in China. NOTE Paragraph 00:11:29.000 --> 00:11:33.000 So the model we've proposed to explain this 00:11:33.000 --> 00:11:35.000 is that when modern humans came out of Africa 00:11:35.000 --> 00:11:38.000 sometime after 100,000 years ago, 00:11:38.000 --> 00:11:40.000 they met Neanderthals. 00:11:40.000 --> 00:11:43.000 Presumably, they did so first in the Middle East, 00:11:43.000 --> 00:11:45.000 where there were Neanderthals living. 00:11:45.000 --> 00:11:47.000 If they then mixed with each other there, 00:11:47.000 --> 00:11:49.000 then those modern humans 00:11:49.000 --> 00:11:51.000 that became the ancestors 00:11:51.000 --> 00:11:53.000 of everyone outside Africa 00:11:53.000 --> 00:11:56.000 carried with them this Neanderthal component in their genome 00:11:56.000 --> 00:11:58.000 to the rest of the world. 00:11:58.000 --> 00:12:01.000 So that today, the people living outside Africa 00:12:01.000 --> 00:12:04.000 have about two and a half percent of their DNA 00:12:04.000 --> 00:12:06.000 from Neanderthals. NOTE Paragraph 00:12:06.000 --> 00:12:09.000 So having now a Neanderthal genome 00:12:09.000 --> 00:12:11.000 on hand as a reference point 00:12:11.000 --> 00:12:13.000 and having the technologies 00:12:13.000 --> 00:12:15.000 to look at ancient remains 00:12:15.000 --> 00:12:17.000 and extract the DNA, 00:12:17.000 --> 00:12:21.000 we can begin to apply them elsewhere in the world. 00:12:21.000 --> 00:12:24.000 And the first place we've done that is in Southern Siberia 00:12:24.000 --> 00:12:26.000 in the Altai Mountains 00:12:26.000 --> 00:12:28.000 at a place called Denisova, 00:12:28.000 --> 00:12:30.000 a cave site in this mountain here, 00:12:30.000 --> 00:12:33.000 where archeologists in 2008 00:12:33.000 --> 00:12:35.000 found a tiny little piece of bone -- 00:12:35.000 --> 00:12:37.000 this is a copy of it -- 00:12:37.000 --> 00:12:41.000 that they realized came from the last phalanx 00:12:41.000 --> 00:12:44.000 of a little finger of a pinky of a human. 00:12:44.000 --> 00:12:46.000 And it was well enough preserved 00:12:46.000 --> 00:12:49.000 so we could determine the DNA from this individual, 00:12:49.000 --> 00:12:51.000 even to a greater extent 00:12:51.000 --> 00:12:53.000 than for the Neanderthals actually, 00:12:53.000 --> 00:12:55.000 and start relating it to the Neanderthal genome 00:12:55.000 --> 00:12:58.000 and to people today. 00:12:58.000 --> 00:13:00.000 And we found that this individual 00:13:00.000 --> 00:13:03.000 shared a common origin for his DNA sequences 00:13:03.000 --> 00:13:07.000 with Neanderthals around 640,000 years ago. 00:13:07.000 --> 00:13:10.000 And further back, 800,000 years ago 00:13:10.000 --> 00:13:12.000 is there a common origin 00:13:12.000 --> 00:13:14.000 with present day humans. NOTE Paragraph 00:13:14.000 --> 00:13:16.000 So this individual comes from a population 00:13:16.000 --> 00:13:19.000 that shares an origin with Neanderthals, 00:13:19.000 --> 00:13:22.000 but far back and then have a long independent history. 00:13:22.000 --> 00:13:24.000 We call this group of humans, 00:13:24.000 --> 00:13:26.000 that we then described for the first time 00:13:26.000 --> 00:13:28.000 from this tiny, tiny little piece of bone, 00:13:28.000 --> 00:13:30.000 the Denisovans, 00:13:30.000 --> 00:13:33.000 after this place where they were first described. 00:13:33.000 --> 00:13:36.000 So we can then ask for Denisovans 00:13:36.000 --> 00:13:38.000 the same things as for the Neanderthals: 00:13:38.000 --> 00:13:42.000 Did they mix with ancestors of present day people? 00:13:42.000 --> 00:13:44.000 If we ask that question, 00:13:44.000 --> 00:13:46.000 and compare the Denisovan genome 00:13:46.000 --> 00:13:48.000 to people around the world, 00:13:48.000 --> 00:13:50.000 we surprisingly find 00:13:50.000 --> 00:13:52.000 no evidence of Denisovan DNA 00:13:52.000 --> 00:13:57.000 in any people living even close to Siberia today. 00:13:57.000 --> 00:13:59.000 But we do find it in Papua New Guinea 00:13:59.000 --> 00:14:03.000 and in other islands in Melanesia and the Pacific. 00:14:03.000 --> 00:14:05.000 So this presumably means 00:14:05.000 --> 00:14:08.000 that these Denisovans had been more widespread in the past, 00:14:08.000 --> 00:14:11.000 since we don't think that the ancestors of Melanesians 00:14:11.000 --> 00:14:13.000 were ever in Siberia. NOTE Paragraph 00:14:13.000 --> 00:14:15.000 So from studying 00:14:15.000 --> 00:14:18.000 these genomes of extinct humans, 00:14:18.000 --> 00:14:21.000 we're beginning to arrive at a picture of what the world looked like 00:14:21.000 --> 00:14:24.000 when modern humans started coming out of Africa. 00:14:24.000 --> 00:14:27.000 In the West, there were Neanderthals; 00:14:27.000 --> 00:14:29.000 in the East, there were Denisovans -- 00:14:29.000 --> 00:14:31.000 maybe other forms of humans too 00:14:31.000 --> 00:14:33.000 that we've not yet described. 00:14:33.000 --> 00:14:36.000 We don't know quite where the borders between these people were, 00:14:36.000 --> 00:14:38.000 but we know that in Southern Siberia, 00:14:38.000 --> 00:14:40.000 there were both Neanderthals and Denisovans 00:14:40.000 --> 00:14:43.000 at least at some time in the past. 00:14:43.000 --> 00:14:46.000 Then modern humans emerged somewhere in Africa, 00:14:46.000 --> 00:14:49.000 came out of Africa, presumably in the Middle East. 00:14:49.000 --> 00:14:52.000 They meet Neanderthals, mix with them, 00:14:52.000 --> 00:14:55.000 continue to spread over the world, 00:14:55.000 --> 00:14:58.000 and somewhere in Southeast Asia, 00:14:58.000 --> 00:15:00.000 they meet Denisovans and mix with them 00:15:00.000 --> 00:15:03.000 and continue on out into the Pacific. 00:15:03.000 --> 00:15:06.000 And then these earlier forms of humans disappear, 00:15:06.000 --> 00:15:09.000 but they live on a little bit today 00:15:09.000 --> 00:15:11.000 in some of us -- 00:15:11.000 --> 00:15:14.000 in that people outside of Africa have two and a half percent of their DNA 00:15:14.000 --> 00:15:16.000 from Neanderthals, 00:15:16.000 --> 00:15:18.000 and people in Melanesia 00:15:18.000 --> 00:15:21.000 actually have an additional five percent approximately 00:15:21.000 --> 00:15:24.000 from the Denisovans. NOTE Paragraph 00:15:24.000 --> 00:15:26.000 Does this then mean that there is after all 00:15:26.000 --> 00:15:28.000 some absolute difference 00:15:28.000 --> 00:15:31.000 between people outside Africa and inside Africa 00:15:31.000 --> 00:15:33.000 in that people outside Africa 00:15:33.000 --> 00:15:35.000 have this old component in their genome 00:15:35.000 --> 00:15:37.000 from these extinct forms of humans, 00:15:37.000 --> 00:15:39.000 whereas Africans do not? 00:15:39.000 --> 00:15:42.000 Well I don't think that is the case. 00:15:42.000 --> 00:15:44.000 Presumably, modern humans 00:15:44.000 --> 00:15:46.000 emerged somewhere in Africa. 00:15:46.000 --> 00:15:49.000 They spread across Africa also, of course, 00:15:49.000 --> 00:15:52.000 and there were older, earlier forms of humans there. 00:15:52.000 --> 00:15:54.000 And since we mixed elsewhere, 00:15:54.000 --> 00:15:56.000 I'm pretty sure that one day, 00:15:56.000 --> 00:15:58.000 when we will perhaps have a genome 00:15:58.000 --> 00:16:00.000 of also these earlier forms in Africa, 00:16:00.000 --> 00:16:02.000 we will find that they have also mixed 00:16:02.000 --> 00:16:05.000 with early modern humans in Africa. NOTE Paragraph 00:16:06.000 --> 00:16:08.000 So to sum up, 00:16:08.000 --> 00:16:10.000 what have we learned from studying genomes 00:16:10.000 --> 00:16:12.000 of present day humans 00:16:12.000 --> 00:16:14.000 and extinct humans? 00:16:14.000 --> 00:16:16.000 We learn perhaps many things, 00:16:16.000 --> 00:16:21.000 but one thing that I find sort of important to mention 00:16:21.000 --> 00:16:24.000 is that I think the lesson is that we have always mixed. 00:16:24.000 --> 00:16:26.000 We mixed with these earlier forms of humans, 00:16:26.000 --> 00:16:28.000 wherever we met them, 00:16:28.000 --> 00:16:32.000 and we mixed with each other ever since. NOTE Paragraph 00:16:32.000 --> 00:16:34.000 Thank you for your attention. NOTE Paragraph 00:16:34.000 --> 00:16:40.000 (Applause)