Conservation Biology

Wednesday, July 19, 2006


Produced by National Geographic in 2003. Please review what Wikipedia has to say about Y-chromosomal Adam as a background to this video. You will need to source at least three Peer-reviewed publications covering aspects of this subject. Please provide your three references (CSE format) as a comment on this posting - you will be using this in your assignment.

By analyzing DNA from people in all regions of the world, geneticist Spencer Wells has concluded that all humans alive today are descended from a single man who lived in Africa around 60,000 years ago.

Modern humans, he contends, didn't start their spread across the globe until after that time. Most archaeologists would say the exodus began 100,000 years ago—a 40,000-year discrepancy.

Wells's take on the origins of modern humans and how they came to populate the rest of the planet is bound to be controversial.

His work adds to an already crowded field of opposing hypotheses proposed by those who seek answers in "stones and bones"—archaeologists and paleoanthropologists—and those who seek them in our blood—population geneticists and molecular biologists.

Over the last decade, major debate on whether early humans evolved in Africa or elsewhere, when they began outward migration, where they went, and whether they interbred with or replaced archaic species has moved out of scientific journals and into the public consciousness.

Wells addresses these issues in a new book, The Journey of Man: A Genetic Odyssey, and a National Geographic documentary of the same title. In a straightforward story, he explains how he traced the exodus of modern humans from Africa by analyzing genetic changes in DNA from the y-chromosome.

"As often happens in science," he said, "technology has opened up a field to new ways of answering old questions—often providing startling answers."

Of course, not everyone agrees with him.

Search for Origins

The use of population genetics and molecular biology in human origins research has been extremely important in helping to resolve a long-running debate on where modern humans first evolved.

According to the multi-regional model, an archaic form of humans left Africa between one and two million years ago, and modern humans evolved from them independently and simultaneously in pockets of Africa, Europe, and Asia.

Wells's work and that of others confirms the more widely accepted Out of Africa model, which says that all modern humans evolved in Africa and then left in several waves of migration, ultimately replacing any earlier species.

"Genetic evidence tells us that Homo sapiens are of recent origin and arose in Africa," said S. Blair Hedges, a molecular biologist at Pennsylvania State University.

"African populations have the most ancient alleles [gene pairs that code for specific traits] and the greatest genetic diversity, which means they're the oldest," Hedges explained. "Our species probably had arisen by 150,000 years ago, with a population of perhaps 10,000 individuals."

Chris Stringer, director of the Human Origins Program at the Natural History Museum in London, said: "The multi-regional model of Homo sapiens evolving globally over a long time scale is certainly dead."

Whether archaic humans and modern humans interbred is another point of debate.
"Given the uncertainties, it isn't yet possible to establish whether we are entirely recent African in origin—certainly my preference—or whether there was a little bit of hybridization/assimilation" between modern and archaic species," said Stringer.

Wells says there is no genetic evidence that supports the idea of intermixing, and several DNA studies actually argue strongly against it.

Journey of Man

Today, there is general agreement that Homo erectus, the precursor to modern humans, evolved in Africa and gradually expanded to Eurasia beginning about 1.7 million years ago. By around 100,000 years ago, several species of hominids populated the Earth, including H. sapiens in Africa, H. erectus in Southeast Asia and China, and Neandertals in Europe. By around 30,000 years ago, the only surviving hominid species was H. sapiens.

But when did we leave Africa and where did we go? Here's where opinions diverge widely. Wells says his evidence based on DNA in the Y-chromosome indicates that the exodus began between 60,000 and 50,000 years ago.

In his view, the early travelers followed the southern coastline of Asia, crossed about 250 kilometers [155 miles] of sea, and colonized Australia by around 50,000 years ago. The Aborigines of Australia, Wells says, are the descendants of the first wave of migration out of Africa.

Many archaeologists disagree, saying the fossil record shows that a first wave of
migration occurred around 100,000 years ago.

"Archaeological evidence suggests that there were modern humans in at least two places in the Levant region of the Middle East 90,000 years ago," said Alison Brooks, a paleoanthropologist at George Washington University in Washington, D.C. "They
disappear from the Levant about 10,000 years later, but could have survived
further south in Asia—we just have no evidence." "There's also evidence," she added, "of Homo sapiens in Australia 60,000 years ago, and they'd have to go through India and Southeast Asia to get there."

Wells agrees that there may have been early human forays into the Middle East, but argues that the Levant of 100,000 to 150,000 years ago was essentially an extension of northeastern Africa and was probably part of the original range of early Homo sapiens. These early settlers were replaced by Neandertals in the region about 80,000 years ago.

"There's a roughly 30,000-year gap in the archaeological record of Homo sapiens outside of Africa," said Wells. "The real expansion occurred in the Upper Paleolithic (around 40,000 years ago) into the uncharted territory of Asia proper."

Brooks agrees there's a gap, but puts it closer to 20,000 years. Richard Klein, an anthropologist at Stanford University, has one explanation for the gap and the subsequent waves of colonization beginning around 45,000 years ago. Klein thinks Homo sapiens may have been anatomically modern 150,000 years ago, but did not become behaviorally modern until about 50,000 years ago, when a genetic mutation related to cognition made us smarter. He theorizes that this change in thinking ability enabled modern humans to craft sophisticated tools, build permanent lodgings, hunt more effectively, and possibly develop language. It also led to greater

Other possible triggers for the burst of migration 45,000 years ago include an increase in population, which spurred competition and innovation; a change in diet, with consumption of more meat and fish; the acquisition of language; and climate change.

Populating the Globe

Wells says a second wave of hominids left Africa around 45,000 years ago, reproduced rapidly, and settled in the Middle East; smaller groups went off to India and China. Isolated by mountains and the sea for many generations, and exposed to a colder climate and less sunlight than in Africa, the Asian populations became paler
over time. Around 40,000 years ago, as the grip of the Ice Age loosened and
temperatures briefly became warmer, humans moved into Central Asia. Amid the
bountiful grassy steppes, they multiplied quickly. "If Africa was the cradle of
mankind, then Central Asia was its nursery," said Wells.

Around 35,000 years ago, small groups left Central Asia for Europe. Cold temperatures kept them there. Cut off from other groups, these migrants became paler and shorter than their African ancestors.

From there, around 20,000 years ago, another small group of Central Asians moved farther north, into Siberia and the Arctic Circle. To minimize physical exposure to the extreme cold they developed, over many generations, stout trunks, stubby fingers, and short arms and legs. Finally, around 15,000 years ago, as another Ice Age began to wane, one small clan of Arctic dwellers followed the reindeer herd over the Bering Strait land bridge into North America. According to the genetic data, says Wells, this initial group may have included as few as two or three men—perhaps 10 to 20 people in all. Also isolated, they too acquired distinct physical characteristics.

Many archaeologists, however, believe that Australia, the Middle East, India, and China were inhabited much earlier.

"The dates don't compare well to the order or the geography of the migration patterns revealed by the fossil record," said Brooks. "Y-chromosome data give
consistently younger dates than other types of genetic data, such as mitochondrial DNA."

Hedges said that "the dates of expansion and colonization discussed by Wells may be correct, but they almost appear to be too recent. Most geneticists are getting data that agree with most archaeological and fossil data." He noted, however, that all of the different methods used for dating can generate errors.

"If you step back a bit and look at the bigger picture, there is a lot more agreement in this field today than there was a decade ago," Hedges said.

Common Ancestors

Wells's work is based on studies of DNA in the y-chromosome. The y-chromosome is a good candidate for population studies such as this because it doesn't recombine as
other parts of the genome do (each parent contributes half of a child's DNA, which join together to form a new genetic combination).

Thus, the y-chromosome is passed on as a chunk of DNA from father to son, basically unchanged through generations except for random mutations. These random mutations, which can happen naturally and be harmless, are called markers. Once a marker has been identified, geneticists can go back in time and trace it to
the point at which it first occurred, which would be the most recent common

As in any scientific work, there are caveats.

The point at which a single common ancestor is found "can vary based on which gene you're looking at, the mutation rate, and population size, and on factors such as whether a bottleneck in the population occurred," said Sarah Tishkoff, a geneticist at the University of Maryland. "Natural selection also plays a significant role." There is another chunk of DNA that also passes through generations relatively unchanged; it is found in a part of the cell called the mitochondria and is transferred from mother to daughter. While the most recent male common ancestor identified through the y-chromosome lived 60,000 years ago, the most recent female common ancestor traced through mitochondrial DNA lived around 150,000 years ago. Whether an individual can be identified as our single common ancestor is open to debate. "There's almost certainly not an Adam or Eve," said Tishkoff. "Each of our genes have their own history, which could be passed on from different ancestors. It's more likely that a lineage can be traced back to a population of 50, 100, or even several thousand people."

Others agree. "The fact that one man apparently gave rise to the y-chromosome genes of all moderns does not mean he was our only male ancestor," said Stringer. "What it means is that his male progeny were more prolific breeders or luckier, and their Y genes survived while those of his contemporaries didn't. But those contemporaries could have passed on many other genes to present-day peoples." That's "absolutely correct," said Wells, adding: "The real significance of the date of our common Y-chromosome ancestor, is that it effectively gives us an upper limit on when our species began to leave Africa."

One point of wide agreement among those who study human origins is that more and more insight will come from closer collaboration between disciplines "Greater discussion and collaboration between geneticists and paleoanthropologists would be good for both," said Stringer. "It's worth bearing in mind," he said, "that studies of recent DNA are studies of the genes of the survivors. Such studies can't tell us anything about non-survivors, such as the Neandertals and Solo Man in Java. We still require fossils, archaeology, and, where possible, ancient DNA for the whole picture of human evolution."

Wells's work described in Journey of Man draws on genetics, palaeoanthropology, palaeoclimatology, archaeology, psychology, and linguistics. "I really see the field as a collaborative, synthetic effort to make sense of our past," he said. "The notion that any single area of investigation, operating in isolation, could have all the answers is ludicrous."

Link to this Review

I was not able to find any real reviews of this video. But I did find this very useful link that shows the routes of both Mitochondrial Eve and Y-chromosomal Adam - can switched on or the other or have both on at the same time! Take some time looking at this - I think it is a great web resource! I am still wondering whether we should not go for the Genetic Testing for each of us and get NISL to pay.... what do you think?

Since I was not able to find any real reviews please provide a 500 word review of this video as a new posting (yes that is longer that for Mitochondrial Eve).




Produced by the Discovery Channel in 2002. Please review what Wikipedia has to say about Mitochondrial Eve as a background to this video. You will need to source at least three Peer-reviewed publications covering aspects of this subject. Please provide your three references (CSE format) as a comment on this posting - you will be using this in your assignment.

What Discovery Channel has to say (I would avoid their website ... it is seriously irritating, may even be the MOST irritating website I have visited so AVOID AT ALL COSTS and I have not provided their URL as a result)

Narrated by actor Danny Glover, "The Real Eve" reveals that our shared genetic heritage links every living person on earth and traces the expansion of modern humans throughout the world. The discovery of the Eve gene stunned the world. It seems we could all be descended from just a few females – or even just one. In this telling anthropological video, we access the very latest DNA reconstructions, and for the first time, tell conclusively the story of where, when and how the human race came about and then populated the world.

The Internet Movie Database [1] said the following about this DVD

Mitochondrial DNA is passed from mother to children, both male and female, unchanged and it mutates at a predictable rate; i. e., the more the genetic mutations in the DNA, the more ancient the origin of the population. Using these facts, some scientists are studying mitochondrial DNA to try to trace back the origins of the human race. Using this method, the scientists have traced the human race to one female in Africa several million years ago.

Then they traced the migration patters of her descendants as they spread across the earth. The Real Eve is a fascinating documentary presenting a new and controversial theory of human evolution. It does what all good documentaries do, it makes you think, and it entertains at the same time. I enjoyed it very very much and anyone interested in human evolution would probably enjoy it also.

DVD Review [2] had the following to say...

The Real Eve is, just that, an Artisan-produced, Discovery Channel documentary based on a new scientific find that traces all modern human races back to one African woman. Not just the first woman, but the one whose genetic make-up was the strongest to survive. This woman's daughters were the most fit to survive, and over thousands of years migrated into Yemen, and then continued to branched out to the ends of the world. The scientific find that has allowed all of this to happen is the discovery of mitochondrial DNA. Mitochondrial DNA holds key marks that tell a scientist exactly which out-of-African branch a subject's ancestors came from. The content of The Real Eve was controversial and exciting all at the same time.

The science of The Real Eve was quite amazing, but the story telling of the journeys taken from Africa to every inhabited part of the world were captivating. With footage of modern-day tribes and re-enactments of ancient tribes, the story is well told. A few times I became confused, but eventually it was easy to put two and two together. I was never lost more than a few moments.

Even more intrigueing was the explanation for our differences in color. The Real Eve explains how each out-of-African branch entered new untouched territory, thus having to adapt to new climates and landscapes. Through evolution, each branch adapted to their new world. The rule of thumb seems to be - the closer to the equator, the darker the skin, and vice-versa.

I learned so many things that were unbelievably interesting. For instance, Native American Indians are not the REAL native americans. An earlier branch of people, that more resemble northern asian tribes, had migrated into the Americas thousands of years earlier. When a branch from Siberia (the ancestors of modern-day Native Americans) migrated into America, a fight over territory ensued and eventually drove out the earlier inhabitants. Small tid-bits of information like this made The Real Eve even more fun to watch.

The only special features on the DVD are two mini behind-the-scenes clips. More like extended 3-minute commercials, these clips provide a small, but interesting amount of information. "The Edge of Extinction" shows how a group of computer effects engineers recreated an ancient volcano from the ground up using CGI (computer generated images). "One Family" is a short, yet insightful, look at the purpose of The Real Eve. Neither clip teaches much, but like a commercial, they convey a few interesting ideas about the show.

Taking a step back from the science of The Real Eve, the documentary has a really nice message about understanding our differences, and better yet, understanding our likenesses. The great story telling and the scientific magnitude of The Real Eve make it seem really silly to fight over our racial differences. When a Greek woman and a Native American man have their mitochondrial DNA analyzed, they find that their heritages both trace back to a Northern Siberian branch of the original out-of-African movement. From this branch, a faction went east into the Americas, while another headed west to Europe. The astonishment moves the woman to speak about tolerance and understanding. There is so much more to all this, but you'll have to watch to really understand it. I really enjoyed The Real Eve and recommend it to anyone who regularly finds themself watching The Dicovery Channel or TLC.

The Apollo Guide [3] had the following review

This documentary was produced by and for the Discovery Channel, which tells you most of what you need to know: it’s competently made, educational and more or less entertaining, depending on the viewer. Personally, I’m moderately interested in science and I found a good deal of The Real Eve compelling, but it can also be tedious.

Andrew Peddington’s film attempts to detail the journey of modern humans from the first tribes in the heart of Africa 150,000 years ago through their expansion to every corner of our planet. Recent advances in DNA reconstruction show that all five billion people living today share the same mitochondrial DNA. This basically means that we’re all related to one of these first women, the “genetic Eve”.

Further genetic tracking allows scientists to follow the development of DNA lines as people divide and migrate. By combining this with the discoveries of archaeologists and geologists, we’re able to recreate how and why this journey occurred. Originally hunters-gatherers, the first people were forced to change their ways when the world’s water became locked in ice and Africa dried up. This first led them to the coastal areas, where they lived by fishing and beach combing, and when they became too many for the limited resources, some of them took off on the first exodus.

Crossing over the Red Sea to Yemen and its fertile grounds and fresh water, the daughters and sons of genetic Eve progressively spread and populated the Middle-East, Asia, Australia, Europe and eventually the Americas. Differences in climate and environment caused them to physically alter over the thousands of years, most notably with skin becoming paler as people moved to colder regions. But underneath the skin, the movie suggests, we are all exactly the same. That humanistic message is the best thing about The Real Eve, and possibly what motivated the filmmakers to make it. People can be so intolerant and xenophobic in our age that it doesn’t hurt to remind them that they’re just variations of the same species.

Unfortunately, the documentary is not consistently enlightening. It’s dynamically crafted, with minimal ‘talking heads’ segments with scientists, instead focusing more on sequences recreating the different stages of modern human’s journey. Sadly, all the impressive camerawork, stylish montages and special effects don’t quite make up for the dullness of the narration, which is read by Danny Glover. The narration is meandering, repetitive and often pointless, as the visuals and the interviews with scientists are evocative
enough on their own.

Also puzzling are the out of place action sequences, like a whole segment about a volcano eruption (recreated with bad computer-generated imagery), a shark attack or a long battle scene between Native Americans. Clearly, Peddington and company want to dramatise things and not make their film feel like a dry lecture, but these action beats are digressive nonetheless. Still, The Real Eve conveys an inspiring message about the unity of the human race and it advances some interesting theories about the migration patterns of our ancestors.

To get the Ball rolling on this course please provide a very brief 200-300 word personal take on this video (not references required) and post as a new contribution to the Blog.

School Exercise based on this video

References and Links







Dr. Spencer Wells The Ultimate Genealogist
(Extracted from

Image Credit

At the headquarters of the National Geographic Society in Washington, D.C., a blond man of 35 with a ruddy complexion strides out of the elevator with bedhead, wearing sandals, shorts, and a wrinkled shirt open to the fourth button. It is Dr. Spencer Wells, geneticist, anthropologist, author, documentary filmmaker, and Texas Ex. Granted, it’s Casual Friday here, but he admits taking the concept farther than most of NG’s other 1,200 employees. In fact, he looks like he’s just crawled out of a sleeping bag on a camping trip, and perhaps there’s a reason for that. If he looks familiar, it is probably due to his PBS/National Geographic documentary The Journey of Man, which aired across much of the country last year. His book by the same name is now out in paperback. In the film, Wells traveled through 12 countries on five continents over the course of a year drawing blood from isolated populations and testing their DNA for markers that indicate a shared lineage. His conclusion? All humans on earth are descended from a single man, who lived in Africa about 60,000 years ago. Through this process, Wells also was able to map the major waves of migration, showing when various populations left Africa and where they went, trailing their DNA evidence behind them in the form of their living descendants. Australians represent the first wave to leave Africa, skirting the Indian Ocean along a coastal route that would have been shorter and more direct then because of lower sea levels. Europeans are traced back first to central Asia, then to the Middle East, then, like everyone else, to Africa.

The title Journey of Man: A Genetic Odyssey (We have this thanks to Nicklaus) is not a sexist throwback, but rather reflects the fact that Wells did his work by tracing markers in the Y chromosome found only in men. (Other researchers tracing mitochondrial DNA, found only in women, have concluded that all humans are also descended from a single woman, also in Africa, but living some 80,000 years earlier than the man, meaning that the “Adam,” as it were, had to have had multiple mates.) Raised in Lubbock, the son of a Texas Tech biologist mother and a lawyer father, Wells remembers wanting to be a historian growing up, and at his core, he sees himself as one still, learning to decode the history book we all carry inside our bodies. But it’s no fluke that Wells has ended up at the intersection of television and science. He cites the James Burke 1979 PBS series Connections, about the history of technology, which he watched as a 9-year-old, as one of the strongest influences on his own journey. “That’s part of the reason I started seeing this connection between history and technology and science,” he says in the smooth but rapid patter born of a thousand interviews. At the same time, his mother went back to school to get her PhD in biology, and he was inspired by hanging out with her in the lab. Having skipped two grades, he arrived at UT Austin at age 16 and graduated Phi Beta Kappa at 19, which meant he didn’t spend a lot of time on Sixth Street. But he recalls going to Eeyore’s Birthday Party and to Antone’s “when they would let me in.” Austin was his first experience in a relatively big city, and he remembers UT as a clearinghouse of a lot of new ideas and credits the University with helping him lay a solid foundation for his career.

In February of this year, Wells was brought back to UT by the Department of Slavic Languages as a guest lecturer. During the question-and-answer session that followed, a man in the audience with a thick accent took a shot at part of his theory, to which Wells grinned warmly and replied, “Did I have you for Developmental Biology?” before deftly explaining away the concern. In addition to Klaus Kalthoff, Wells fondly remembers Mark Kirkpatrick, a population geneticist who acted as a kind of unofficial advisor.

As an undergrad, Wells did an independent study with him in theoretical population genetics, and Kirkpatrick encouraged him to apply to Harvard to work with renowned geneticist Dick Lewontin. “It’s really all about finding out what you’re excited about and then going out and finding the best place to do it.” At 19, it was on to Harvard to pursue his doctorate, then Stanford. Wells left Stanford in 1998 to collect blood samples and do DNA analysis in the former Soviet republics of the Caucasus and central Asia. He then worked at Oxford and, later, as director of research at a Massachusetts biotechnology company, before signing on as a fellow with the National Geographic Society. “I’m very lucky,” he says. “It is one of those gold-standard names. I’ve been to some really hairy places in obscure parts of the world and there are two names that they recognize everywhere, and that’s BBC and National Geographic.”

We spoke on May 7, on the patio outside the National Geographic headquarters in downtown Washington...

A: I tend to think of you as the ultimate genealogist. I wonder if you’ve ever been interested in tracing your own family tree.

SW: That’s a good way of putting it. A little bit. That’s the sort of thing I suppose you get more interested in as you get older. When you’re a kid you tend to be concerned with girls and cars. But certainly recently, I’ve been more interested in that. In fact, the Wells family has one of the largest ongoing DNA genealogy projects in the world, and I’ve done a little bit of consulting for that. It turns out I’m probably related to Governor Thomas Wells, one of the early governors of Connecticut who came from Warwickshire in England. My mother’s maiden name is Constable, and I’m distantly related to a painter who lived in East Anglia, John Constable. So I know a little about the last few generations, but as with everybody, it runs out after a while. Once you get back to three, four, five generations ago, you hit a brick wall. That’s the great thing about DNA, you can go back farther than that, all the way back to the beginning.

A: So in a way you’ve been working your family tree from both ends.

SW: Definitely. But the way we do these studies is starting in the present and working back into the past, which is turning everything on its head. Historically, paleoanthropologists have gone out and dug things up out of the ground that looked vaguely like us. And they’d compare them and say, “Well, morphologically, this is more similar so perhaps this is our direct ancestor,” and someone would discover something else a few years later and say, “No, this is our direct ancestor.” That’s fascinating and provides us a lot of possibilities about our past, but it doesn’t, I would argue, give us the probabilities, and that’s what genetics does because it’s a large body of data and it gives us a statistical set to test some of these hypotheses about our origins and migrations.

A: A lot of people probably take anthropological findings with a grain of salt. “Here’s another theory that’s going to be exploded in a few years when they find another jawbone somewhere else.” Is the single origin of humanity a fact or is this still in the stage of a theory?

SW: All science is in the stage of theory. We cannot travel back in time and know exactly how things happened in the past. That is the nature of historical science. What you have to do is to glean clues from lots of bodies of evidence. The book is a synthetic view of those clues. It’s based on the genetic results, and that is what I’m armed with uniquely as a geneticist, but I’m drawing on material from paleoanthropology and archeology and linguistics and climatology and lots of other fields to really test the hypothesis: does this make sense? To do that we have to go out and check the genetic results that we get by looking at other fields. And the answer is yes, they do make sense. If you take a critical view of all of these other fields, things start to fall into place, and we are developing a coherent picture of our past. We may modify some of the details. And we certainly don’t have as many details as we would like, so there’s a lot of work to be done, but the big broad-brush picture of where we came from and how we made it around the world — yeah, we’re pretty confident about that now.

A: You talked about being descended from this governor. People are naturally intrigued by the fact that they’re descended from William the Conqueror or, in the Arab world, from Muhammad. But isn’t it true, that when you’re dealing with distances of a thousand years, that virtually every white person is directly descended from William the Conqueror and virtually every Arab is descended from Muhammad?

SW: Yes. It’s a simple mathematical problem: You have two parents and four grandparents, et cetera. And it goes 2n where n is the number of generations. You go back 50 generations and it’s 250, which is a huge number; it’s more than the total number of people who have ever existed in the history of life on earth. So obviously, it has to be less than 2; it’s 1-point-something, and that point-something reflects the fact that we are somewhat related. You don’t have two completely unrelated parents. Everybody is related to a certain extent.

A: Everyone is the product of incest?

SW: Inbreeding, exactly. What we study, I sometimes say jokingly, is the history of who had sex with whom, and that can be a little complicated at times. (Laughs) A: Briefly, how do you come to this timeframe of 60,000 years?

SW: Big question. We use this molecule, DNA, which is contained in every cell in our body. (Our red blood cells kick out the nuclei when they become mature, so they don’t actually contain any DNA, but pretty much every other cell in our body does.) This is the blueprint to make a version of you. You have to pass on half your DNA to your child in a shuffled way, a process called recombination. DNA is very long. It’s made up of four nucleotide bases — A, C, G, and T — and it’s the order of those that provide the information. Because it’s so very long — it’s three billion of those in length — you occasionally make a mistake when you’re copying it and passing it along. Those are called mutations, and everybody carries some mutations that distinguish them from their parents, roughly 30 of them per genome per generation. When those are passed on through the generations, they become markers of descent. They occur very rarely, so the odds are that most sites are not going to have any. When they do happen they occur uniquely at a single site. You hardly ever mutate the same site twice. So when two people share these markers in common, it’s a sign that they share ancestry at some point. What we do is start in the present with DNA from people who are alive today and trace back through these lineages that are defined by the markers that have been passed on through many, many generations, back to the point where they share a common ancestor. When we do that with people who are members of the same family, we very quickly reach a point where they share a common ancestor. But, it turns out, we can also do that with people all over the world. By asking a really stupid question (it’s pretty much hypothesis-free): “Are we related, and if so, how are we related?” we trace back to a single ancestor on the Y chromosome, which, it turns out, is the most recent ancestor we all share. This man, this Y chromosome, existed 60,000 years ago. And it turns out he existed in Africa. That means our species was still limited to Africa in its distribution 60,000 years ago. It’s only in the last 60,000 years, or 2,000 generations, roughly, that we have left Africa to go out and take over the world.

A: So it’s these 30 mutations per genome that’s the key to the timing?

SW: Yes. In addition to allowing us to trace these lineages, we know the rate at which the mutations occur. So if we count up the number of mutations on each lineage, and we average that, we can say with pretty good confidence the length of time that the lineages have been accumulating. So we look at the level of diversity, and because the level of diversity is determined by the rate at which this mutational clock is ticking, we can say something about when they started to diverge.

A: As for racial differences, it’s easy enough to understand that people in northern climates evolved lighter skin to let in more sunlight and produce more vitamin D, as you describe in the book. But what explains the other differences between the races: hair texture, eye color, musculature, even bone structure?

SW: A lot of it is probably random. Population geneticists like to talk about a process known as genetic drift. Whenever the population size is very small, you can get rapid changes in gene frequency. That gene frequency could be a genetic variant that determines what type of hair you have or the color of hair you have. And genetics could be understood as a sampling process. If you flip a coin a thousand times, you would expect to get roughly 50 percent heads and 50 percent tails. You’d be surprised to get 700/300. If you only flip that coin 10 times, you might very likely get 7 and 3 or 4 and 6. That occurs in the same way in a small population. So when you’re sampling the genes from the present population to produce the genes of the subsequent population, and you only have a few individuals to sample from, then you’re going to get a skewed or biased estimate, so you’re going to get changes very rapidly. Because human populations were relatively small when we were hunter gatherers, drift probably played a big role in setting in motion some of these changes in frequencies that have caused us to diverge. I would argue that that’s not the only answer, because we do seem to be so very different given how recently we started to diverge. It’s only been in the last 40,000 to 50,000 years and in many cases, only the last 10,000 or 20,000 years that we started to split off from each other. And that suggests that selection has played a role, and that the evolution has been more rapid than you’d expect due to this drift process. Probably the best hypothesis, although we’ve never tested and it would be great to do so, is Darwin’s hypothesis of sexual selection. We choose people to mate with on the basis of what we find attractive, and that varies according to where you are in the world. There’s a village in Romania where all of the women have mustaches. I don’t see this becoming universal, thank God, but maybe in that little corner of the Balkans, that could become a defining racial or ethnic characteristic simply because the men find that attractive. So these simple local decisions about likes and dislikes, summed over many generations, produce, we think, some of these massive differences of appearances.

A: So let’s say it did. For the population as a whole, that might manifest itself in increased hairiness in men and women, assuming facial hair is a sign of increased
testosterone, right?

SW: Perhaps. It might be a testosterone thing, or it might be something that’s specifically about facial hair in women. We don’t understand the genes underlying most of these traits, and until we do, we can’t go out and test the hypotheses. This is something that’s really going to have to come out of work from the Human Genome Project, figuring out which genes determine human morphology.

A: What’s our best guess right now as to how long it takes to create a distinctive race? Let’s say you take a population from Ghana and move them to Sweden. How long until they become white?

SW: It could probably happen quite rapidly, over the space of a few hundred generations, maybe 10,000 years or so. It depends on the selection pressure. I was reading a story the other day about African American women living in very cold climates. They are breast-feeding their children, but they’re not generating enough vitamin D through this process where you can produce it if you’re exposed to UV light. They’re not getting enough in their diets either, and their children are ending up with rickets, a horrible, debilitating childhood disease. If you’re a hunter-gatherer, and you’ve got rickets, you’re not going to survive very long. So the selection pressure could have been quite intense as people got up into these higher latitudes. And anybody who allowed even a little bit more UV light through and produced just enough vitamin D to survive would have a huge advantage. They would tend to have more children; their children would have more children; and that’s the way natural selection works.

A: Like a lot of Americans, my family tradition is that I have some Indian blood, Cherokee and Mohawk, but we don’t know exactly how much — 3/64ths or 1/16th or what have you. Is there any way to quantify the ancestry of a mixed-race person?

SW: We don’t really like to talk about races. We talk about lineages being at high frequencies in particular populations. Races really have no meaning biologically, certainly not genetically. Now, if you’re asking, “Do I have ancestors who came from the indigenous groups living in North
America?” we could address that. But at the moment it’s very difficult to talk about dividing your genome up into 17 percent whatever. There are companies out there that will do this for you, but I don’t necessarily buy the results they are giving you.

A: So it’s a yes/no question, in that you could tell me if I had some Indian ancestry, but not necessarily quantify it as a fraction?

SW: You can’t necessarily say “no,” because you just may not have sampled the region of the genome that you got from your Native American ancestors. But there are markers that are pretty much limited to Native Americans from North or South America. Certainly if you saw one of those, then it would be good evidence that you do have Native American ancestors. But it’s difficult to rule out anything. We’re not really like a martini mix where you add a quarter vermouth and three-quarters gin and then shake it up. Human populations have historically
moved around and mixed a lot, so we tend to share most of our markers. In fact, 85 percent of the genetic variation within our species can be found within a single population. That’s a sign that, yes, we’re all effectively part of an extended family, one extended population. Part of the reason that the Y chromosome is such a good tool for doing these studies in migration is because
it has changed a little bit more between populations. In most indigenous groups, a few men tend to do most of the mating. And their sons tend to inherit whatever allows them to do that: social standing or wealth or sexual prowess or whatever it is. So that, over time, tends to accentuate the differences between populations on the male lineage, the Y chromosome lineages. Most of the genome doesn’t show those extreme differences.

A: Speaking of moving around and mixing, what is the oddest anthropological fact or anomaly that you’ve come across? Is there anything that cannot be explained by this theory?

SW: The whole problem of Australia. If you’re looking at the archeological record for the presence of modern humans, clearly that appears first in Africa, and we have anatomically modern humans now dated to 140,000 years ago. Our species probably originated as a discernible physical entity around that time. We stay in Africa until roughly 50,000-60,000 years ago, then we start to leave. Amazingly, the next place outside of Africa that we start to see anatomically modern humans showing up is in Australia. It’s not in the Middle East; it’s not in India. So, yeah, that doesn’t make a lot of sense, but genetically you can trace this trail where you see evidences of the genetic lineages that lead to Australia along that route, even though you don’t see the archeological evidence. So in that case, you’ve got genetic data, but the archeology hasn’t really caught up yet. It suggests that you might be better off wearing scuba gear rather than a pith elmet and searching offshore in India because the sea levels were once much lower. And if these people were on the coast taking the smartest route to Australia, as we believe they did, maybe the evidence is underwater. The earliest evidence of fully modern humans in India is in southern India around 32,000 years ago. So 20,000 years after we see it in Australia? A bit worrying. But again, we’ve got a prediction and think we can go out and test it. The Europeans coming out of central Asia — that’s a curly one. That’s surprising, but it makes sense if you imagine that these people who composed the second main wave out of Africa that went up via the Middle East would have been grassland hunters. They would have been people used to living on the savannahs of easternAfrica hunting antelope and such. And if you just look at where the grasslands are found, they’re not found in the Balkans, which is what would have separated
the Middle East from Europe, which are mountainous and forested. The grasslands would have extended into central Asia and from there, they spread out along the steppe belt to France in the west and Korea in the East. So if you think about people — instead of trying to traverse a continent or make it into Europe —simply looking for more food, if the food is on the grasslands, the grasslands lead you to central Asia.

A: It was the path of least resistance instead of some sort of prehistoric Lewis and Clark thing?
but the main wave came later via the grasslands because we were highly adapted to living

A: What about European-type prehistoric remains being found in the Americas?

SW: Most of the early Native American remains dating from 9,000-11,000 years ago, the few that have been studied, look a little more European than today’s Native Americans. That’s not because Europeans made it there before the Native Americans, whatever that would mean. I believe that it is because these ancient central Asian populations who gave rise to both the first wave of expansion into Europe and into the Americas would have looked perhaps a little more European than today’s Native American population. In fact, we know that there was a second migration into the Americas from further east in Asia, and it is a possibility that this second wave is what gave present day Native Americans more of an east Asian or Mongoloid appearance.

A: Isn’t our able to figure these things out closing rapidly?

SW: It’s really just coming out of the Human Genome Project in the last 10 years that we’ve had the technology to do this work. And yet, the things that set in motion that scientific wave of advance have also set in motion a cultural wave of advance, which is leading to globalization of the loss of indigenous cultures that can give us the signposts of this journey. These indigenous groups are being absorbed into the global monoculture at an ever-increasing rate. How many
populations are there in the world? We don’t know for sure. But language can be used as a proxy for population, because language has taken hundreds of thousands of years to develop and requires some degree of cultural isolation to do that. There are roughly 6,000 languages spoken in the world today, and between half and 90 percent of those are going to be gone by the end of the century. They will have been lost because the people speaking them have been absorbed into this global culture, and they’re speaking another language, and their children never learned how to speak their parents’ language. Suddenly you’ve lost all sense of cultural identity. When that’s gone, yes, the genes are going to live on, and genetic variants are still going to be found in cities like Rio and Bombay and New York, but there’s no cultural and historical context. So it makes our job virtually impossible, therefore we’ve got a closing window of opportunity because we have the technology but we’ve nearly lost the samples, the people that we need to study.

A: So this window is closing at the very moment we’re able to use it?

SW: Here’s an example. We’ve recently determined that 8 percent of the men of central and eastern Asia carry lineages that trace directly back to Gengis Khan, and because it’s so populous in Asia, that equates to about one in 200 men all over the world. (That made a Harper’s List. That’s my real claim to fame. You know you’ve made it when you make a Harper’s List!). We know this because this lineage originated in Mongolia roughly 800 years ago, and its highest frequencies are in populations that claim to be his direct descendants, particularly the Hazara in northern Pakistan, who look more Mongolian than the surrounding population. Without the Hazara, it would have been very difficult to tell that Gengis story. And those are the populations we’re going to lose in the next few years. Why? Their farms are not productive. It’s easier for their kids to move into the city. They don’t want to live this hard life out in the fields. They want to drive a cab or maybe go to school. They don’t speak their local languages when they get to the city; they speak Urdu or whatever the dominant language is in that part of the world. Their kids will lose any sense of connection to that population. Then they’ll marry people that they meet, so the genes disperse. You could probably sample all of these lineages that we’ve talked about by going into a nightclub in the East Village in New York in one, quite literally potentially interbreeding population. And in another generation, we’re all Tiger Woods. It’s really about this whole European Age of Exploration, modernity and industrialization and massive increase in population size. All of these forces are the subject of my next book called Great Leaps Forward, about who we are biologically, and the fact that biologically in many ways we are mismatched with the culture we’ve created in the last 10,000 years. And where are we going in the future?

A: What do you mean by mismatched?

SW: I mean things like the obesity epidemic, increasing diabetes, children on Ritalin, high levels of suicide and depression — ever-increasing levels of those in the developed world, certainly. Our biology is clearly mismatched with some of the aspects of culture, the way we live today. How did this society arise? If it’s so bad for us in so many ways, why do we have it? And going into the future, what are we going to change about ourselves in the society? It’s amazing to think that we are the first species in the history of evolution that has evolved to the point where it can change its own biology. We have the tools of genetic engineering now. We can craft our own
evolutionary fate. Where are we going to go? That’s a big responsibility, and I would argue that to understand where we need to be going in the future, we need to look to the past and understand where we come from.

A: Are there any other historical figures like Gengis Khan on whom similar work’s been done?

SW: The one that I’d like to see is Alexander the Great. Again, we don’t know exactly where he’s buried; we assume it’s somewhere in Baghdad, but we haven’t recovered the body. Yet we know that he was this major historical figure, and he traveled all over and had multiple wives and probably sired children. And just to find a trace of him or his armies would be great. We
haven’t found it yet, but we’re still looking.

A: Did humans and Neanderthals ever live side-by-side?

SW: They did, we believe, because we see evidence of Neanderthal remains at 30,000 years ago, and we know that modern humans were in Europe by around 35,000 years ago, so there must have been some overlap. There was certainly temporal overlap, and we believe that they probably did know about each other and encounter each other’s material culture. There is no evidence, though, for any interbreeding in the genes of people alive today. Modern Europeans seem to have come out of Africa with everybody else, and they didn’t descend from the Neanderthals and in fact it doesn’t seem like there was any mixture between these incoming groups of modern humans of African origin and the Neanderthals that were already there. The Neanderthals were like distant cousins who split off maybe 500,000 years ago from the lineage that later gave rise to us.

A: How would we know if there was any interbreeding?

SW: We have this coalescence point – this Adam – who lived 60,000 years ago in Africa. We have knowledge therefore of the level of diversity we expect to see in the human species, which is all in the last 60,000 years. If we saw a lineage, particular one limited to southwestern Europe, where we know the Neanderthals were living, that fell well outside of that and coalesced to 500,000 years ago, that would be good evidence that it was Neanderthal in origin. We do not see that. All of the European lineages we look at trace back to Africa within the last 60,000 years.

A: Is it possible that it’s like the case of the horse and donkey making a mule, which is sterile?

SW: There are lots of scenarios. One is that we killed them off. That’s not very likely, because we don’t see any direct Neanderthal Waterloo evidence. The other is that we out-competed them. But there was this overlap and therefore the potential for interbreeding. Why didn’t it happen? One possibility, like you suggest, is that maybe we could form an F1 hybrid – a first-generation hybrid – but those individuals would have been sterile, like a mule. It’s possible that we just didn’t find them attractive and ddn’t want to do that. It’s possible that there may have been some kind of infanticide: The father didn’t like the fact that the mother had been impregnated by a Neanderthal or the mother didn’t want to care for the baby. Whatever the case, the end result is that we don’t have those Neanderthal lineages.

A: I’m sure you’re asked a lot about the religious implications of your work. What are those implications in your own mind?

SW: Religion is about faith. It’s not about proof. And therefore, science can’t really address religious issues. Because if you believe in something, and it’s important for your sense of self and who you are and which culture you belong to, you’re not going to turn to science for answers. You’re going to believe the stories that are in your book. If it’s the Bible, great. Maybe it’s the Koran, or whatever your religion is. It is about faith in those. Now, it is interesting that he point that we have reached in our scientific research is in line with a road vision of what is written in the Bible, i.e., we all came from one place as a species, we all spring from a common source, and that therefore people are all part of a big extended family. Now, the timing is a little different. If you count back through the generations mentioned in the Bible, you get back to 4004 B.C. for Adam and Eve. We’re talking about a date tens of thousands of years earlier than that.

A: A decimal error, perhaps?

SW: Yeah. (Laughs) It’s comforting to me. I’m no longer a practicing Christian but was raised a
Christian. You do reach the same sort of point, and this should be a message of hope about human relationships and the fact that we should see each other more as family members.

A: Race is such a loaded topic, here, but really all over the world. What sorts of conflicts have you run into because of this single-origin finding?

SW: Certainly there are groups in America who I think would not like to hear this. There are some scientists who want to believe that we evolved separately in different parts of the world. In particular, there’s a strain of Chinese anthropology that wants to believe that they evolved somewhat separately, from Homo erectus in China, and that they’ve been separate from the
rest of the races or the peoples around the world for a million years or more. There’s no good genetic evidence for it. That’s all I can say. At the end of the day, I’m a geneticist, and that’s my unique contribution. Again, people can have faith in lots of things. And I can present them with my evidence and argue with them, but I can’t twist their arms and force them to accept it.
A lot of these indigenous groups have this very clear sense of self and their connection to the land where they live. In the film, there was an Aboriginal artist saying, “I don’t buy your results. I know we’ve always lived there.” They have their songlines that talk about them being sung into existence from witchetty grubs and gawanas and from the land itself. You know, this is probably a good thing socially and environmentally — to feel that strong sense of connection to the place and to feel like a part of a continuum and that you can’t separate and conquer nature — it’s not a conflict between you and the land and you and the other animals — you are part of this one continuous whole, this ebb and flow of life, etc. That’s probably a good thing in many ways, but obviously it contradicts some of the scientific results, and not everybody could have been born or evolved in the place where they are living today. In fact, most of us have to have moved here from somewhere else, and ultimately, that somewhere else is Africa. So sometimes it’s hard to get indigenous groups to accept the results that we get from their DNA. But again, that’s not my role. My role is to provide the results. To discuss them. To explain them. I’m very interested in the stories they tell us. But people have their own sense of who they are, and I
can’t force them to accept what I present to them.

A: Graham Hancock is a best-selling author who combines astro-archeology, geology, and climatology to make the case that there was once a great civilization, possibly a world
civilization, that was virtually wiped out by earth changes, such as a pole shift leading to radical climate changes and flooding, or rapid, catastrophic ice age meltdowns. I wonder if any of your research refutes or lends credence to this persistent belief among many of a lost civilization?

SW: Certainly there is good evidence that there were past societies that were inundated or were abandoned because of climatic change. There were the Pueblo Indians in the American southwest. The Anasazi abandoned many of their sites, about 700 or 800 years ago, we believe because of a climatic shift after which desert conditions prevailed, forcing them somewhere else.
We think climate change probably contributed to the downfall of the Harappan civilization of the Indus Valley. It may have allowed the Indo-European-speaking groups living in the steppes of
central Asia to invade the subcontinent. So, yes, clearly that has played a role. And even before that, the ice age probably played a critical role in creating our fully modern brain, which allowed us to go out and conquer the world, gave us the tool we needed, this adaptive tool, to live in situations in Siberia or to make it across the straits to Australia — to make it through Beringia and down into the Americas, things that no other hominid species had been able to do. It’s because of this brain. In terms of disappeared civilizations, you’re really talking about a phenomenon of the last 10,000 years, what we would call modern civilization. It’s really since the advent of agriculture, where you have people accumulating excesses of wealth and the rise
of social hierarchies and reasons to build armies and empires. It’s a complicated series of sociological constraints that gives rise to these empires. I would say that, except on local levels, no, we probably haven’t had some massive global intelligent empire that then collapsed, and we all went back into the Dark Ages, forcing us to re-evolve new systems of government, etc. Locally, yes, but in terms of a global collapse, no, I don’t see the evidence for that.

A: What about these megalithic cultures like the ancient Egyptians or the Maya or Olmec?

SW: So you’re talking about pyramids. Pyramids are pretty simple structures. They’re basically artificial mountains. If you take a handful of sand and drop it slowly, you will form a natural pyramid. All you’re doing is reconstructing that out of stone. I don’t think that that alone suggests that there is some connection between those cultures. There are other intriguing
possibilities. Could the Phoenicians — the great seafarers of the Mediterranean in the first millennium B.C. who probably made it to the Azores in the middle of the Atlantic — have made it to the Americas, and maybe communicated some ideas from the Old World to the New? It’s a possibility. But you have to look for very specific evidence. And you have to look, in particular, for synapomorphies — shared, derived characteristics. You could imagine pyramids, being relatively simple structures, being kind of a default. They’re not necessarily a derived, complicated structure. But if you had a similar language being spoken in the Americas to what was spoken in the Old World, yeah, that would be pretty bloody good evidence that there had been contact. And we have an interesting example of that in Madagascar. The Malagasy people speak a language that is closely related to the one spoken in the Pacific. It’s because one small branch of Polynesians went west across the Indian Ocean and made it to the east coast of Africa around 1,200 years ago. So you’ve got this weird discontinuity in Africa of this language that comes from somewhere else.

A: You said that the ice age played a role in forming our fully modern brain. Where does that leave the people who stayed in Africa, or migrated to other locations in the south like Australia or India?

SW: What needs to be made absolutely clear is that the “Great Leap Forward” occurred in Africa, and this is what gave our ancestors the intellectual firepower they needed to go out and colonize the planet. Thus, everyone who left was in possession of roughly the same intellectual potential — there’s no evidence that our basic neurobiology changed as we migrated into new
areas. What is clear is that our culture changed. In northern environments, with their difficult lifestyles, we developed things like microliths (small stone tools that made the best use of rare toolmaking materials), portable shelters, and warm clothing. While the southern coastal route may not have been as challenging as traversing the Siberian ice age (perhaps this helps to explain why Australian aboriginal tools were fairly primitive by Upper Paleolithic standards), we still needed advanced problem-solving skills. We had to make it across a hundred miles or more of open ocean to reach Australia, for instance. nd once we reached Oz, the hardships of living in the driest continent on Earth would have kept us on our toes!

A: Tell us a little about your working conditions during this project. Did you ever fail to get a blood sample that you felt you really needed?

SW: Oh, sure, but usually it’s because people are afraid of the needles. Most people are really interested in their history. And again, we all have some kind of concept of who we are in our family tree, where we came from. But it’s kind of vague for most of us. When you start talking to people about the fact that they’re actually carrying a history book that may have the answers inside their body, and we’re helping them to read that, they tend to get really excited about that. If they want more details we can start to explain DNA, but a lot of these people are not well educated by any stretch of the imagination, so understanding the details of the genetic analysis is a little bit tricky. At its essence it’s about reading that history book.

A: What were some of the toughest episodes that you went through?

SW: I had a situation in Georgia, actually, where we were collecting in South Ossetia, which is a former breakaway region just north of Tbilisi, the capital. The Ossetian people speak an Indo-European language in amongst all the south Caucasian languages spoken in the region, and they have a sense of being very different from the surrounding Georgian population. Because of that, they’ve tried to break away and form their own republic. So there’s a little bit of animosity between them and the Georgians. To work in Georgia, we obviously were collaborating with Georgian scientists. So we went up there with the scientists and started talking to the people about the project. They were kind of interested but a little suspicious. In the end they said, “No, we’re not going to give you any samples.” And we came back the next day and starting talking to
them again, and it turned out that when we got them alone, they said, “We’re not so concerned about you or the project; we think it’s kind of cool. But we don’t trust these Georgians you’re working with. We’re a little bit worried that they’re trying to inject us with some biological weapon.” So in that case we had to actually distance ourselves slightly from our local collaborators. It was really about convincing them that this was about basic science, not about trying to kill them.

A: Were you ever in any kind of political danger?

SW: We pushed the boundaries of what you can do politically. We haven’t done anything illegal, but we had a team go into Iran back in 1998. We were some of the first American scientists who had been allowed to do work there with, again, local Iranian collaborators. We had initially planned this as a driving expedition. We drove from London to Mongolia in a Land Rover, and we were at the border crossing between Azerbaijan and Iran. It is very difficult to get through if
you’re a foreigner, and we didn’t have the right stamps, so they weren’t going to allow the car through. We could have walked across, but we would have left this very expensive vehicle sitting in Azerbaijan. We needed special dispensation from the embassies, and the Americans told us that they had no formal relations with Iran at that time, so we couldn’t get it. Part of the team had to fly down to Teheran and just work on the ground without the machine there. The machine was in my name, so I had to ferry it across the Caspian to Turkmenistan, and we met up on the other side. So, yes, you encounter olitical difficulties, and it’s gotten quite difficult in places like Tajikistan, where you have breakaway regions and rebels, and the central government doesn’t necessarily control the area that you want to go to. You have to make a whole new set of connections and contacts, and you have to work with local warlords.

A: You’ve led an intensely cosmopolitan life. Is there’s any Lubbock left in you?

SW: Yeah, a little bit. I still miss the wide open spaces. I still love just getting into a pickup truck and driving and not seeing anybody else out there, and watching the sunsets out in West Texas — the most beautiful sunsets in the world — all the dust in the air I guess. Drinking a cold Lone Star — yeah.

A: Have any of the places you’ve been reminded you of home?

SW: Central Asia. I think that’s part of the reason I’m drawn to it, oddly enough. I’ve spent a lot of time out of Texas as an adult, but it’s kind of like going home when I get there because it’s very dry, and it’s grassland, and you see cows wandering around. It’s very much like home. laughs)

Avrel Seale, from The Alcalde (July/August 2004)