The DNA Files: Unraveling the Mysteries of Genetics
“DNA and Evolution: Where Did We Come From? Where Did We Go?”
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“DNA and Evolution: Where Did We Come From? Where Did We Go?”
(Theme music begins)
JOHN HOCKENBERRY: This is The DNA Files, I’m John Hockenberry. Scientists say all life contains the same genetic building blocks and just how we’re related is written in our DNA.
DR. KENNETH KIDD: We can compare the DNA sequence we find in modern humans with that in chmips and gorillas.....and see how similar the DNA sequence is..
JONOTHAN MARKS: There's a cultural assumption here, and that is that the genetic similarity overrides all other kinds of differneces. //// If you can't tell the human from the chimpanzee at twenty paces you're not a very good biologist.
JOHN HOCKENBERRY: What does it mean to be related to chimps, to apes, to each other? Genetics adds new fuel to some old debates about human evolution. Coming up, the Goddess of Memory helps us understand DNA and Evolution: Where did we come from and where did we go?
JOHN HOCKENBERRY: The Oscar-winning documentary for 1951 was the tale of four Norwegians and a Swede who crossed the Pacific from Peru to Tahiti on a primitive balsa-wood raft-voluntarily! The voyage of the Kon Tiki was anthropology of the epic school. Thor Heyerdahl and his crew hoped to prove that the people of Polynesia could have come from South America. Alas! scientists believe quite differently today, in part because of a tale told by DNA, as John Rieger reports.
JOHN RIEGER: He was a Norwegian in Polynesia in the 1930s, an adventuress young biologist who rejected the accepted wisdom. Although the Polynesian islands are situated closest to America, it has nevertheless been assumed that these people originally came from the Asiatic fringe, the cradle of the human race. Thor Heyerdahl believed that the first Polynesians must have come west from South America and he set out to prove it.
On a crude balsa wood raft modeled after the boats of ancient South Americans, Heyerdahl and a crew of four set sail from Peru in 1947, casting his theory’s fate and his own to the Pacific. The voyage of the Kon Tiki was a great adventure and an Academy Award winning documentary. Unfortunately, Heyerdahl was wrong.
PROFESSOR REBECCA CANN: The resounding answer from human genetics is no, Polynesians do not come from South America. They most assuredly come from probably some part of Southeast Asia.
JOHN RIEGER: In the early 1980s Professor Rebecca Cann a molecular biologist at the University of Hawaii began studying a rare genetic mutation, a tiny fragment of DNA that seems to appear in people of Southeast Asian heritage no matter where they live today.
REBECCA CANN: Then when I began working in the Pacific uh we discovered that they were a very high frequency of Tahitians, of Marquesans, of Easter Islanders, of Hawaiians, of Cook Islanders.
[waves crashing in background]
JOHN RIEGER: Here was genetic evidence that Pacific Islanders had come from Southeast Asia, but how, and by what route? In order to figure that out, Cann turned her attention to another bit of DNA known to be hyper variable. This DNA mutates so frequently that each new settlement established during some ancient migration would have its own genetic signature. But to decide which mutations and which settlements came first, Cann would have to look several thousand years into the genetic past.
REBECCA CANN: You try to reconstruct what were the ancestral mutations and which are new ones which have appeared in a certain period of time and are restricted geographically, or ethnically or culturally in some way. If you understand those rules, then you can connect a series of mutations to their ancestral state and keep going back and back and you have a reconstructed ancestor.
JOHN RIEGER: Cann’s DNA evidence suggests that the first Polynesians spread from Southeast Asia. But scientists in other disciplines have questions of their own. How did they cross the sea?
Thor Heyerdahl believed that the colonizers of the Pacific couldn’t sail into the wind. Wallowing and virtually unsteerable, the Kon Tiki drifted westward from Peru washing ashore after 101 days on an uninhabited island near Tahiti. But today there is evidence that the first Polynesians came eastward in canoes. Linguists have traced the Polynesian vocabulary of canoeing to Asian languages. A rich oral tradition including the songs of the hula speaks tellingly of certain regional flowers, fish and birds. There is one piece that doesn’t fit though, the sweet potato. It’s a staple of the Polynesian diet. It came from South America.
REBECCA CANN: Horticulturists have DNA sequences from the sweet potatoes and they can actually identify that the cultivar is the same germ plasm. In vernacular English that means that it’s the same identical DNA sequence present in South America and present in the Pacific Islands.
JOHN RIEGER: This piece of genetic evidence remains stubbornly undigested. Could the ancient Polynesians have sailed to South America into the wind and then returned bearing yams. Ironically, scientists today are taking a page from Thor Heyerdahl trying to reconstruct the sailing technology that could make such a voyage. Rebecca Cann.
REBECCA CANN: We say as geneticists this is likely but the people who actually attempt to reconstruct how it’s done, they...they are showing us what it might have been to actually experience it historically.
JOHN RIEGER: So, Thor Heyerdahl’s main theories may have been wrong, but the Kon Tiki did not sail in vain.
I’m John Rieger for The DNA Files.
JOHN HOCKENBERRY: This is The DNA Files, I'm John Hockenberry. Today we're going be asking what DNA can tell us about our origins: about our past as a species, our relation to all
other forms of life, our history.
And so, that's why I went to the computer store just now and brought back this CD-ROM here. It's a new software program called Mnemnosyne 99. Mnemnosyne was the Greek goddess of memory, I believe. Anyway this is supposed to be a fantastic program. It's got all the latest genetics and physics and biology and - well, let's just stick it in the computer and fire it up…right, here it comes...
MEMNOSYNE: Greetings, bipedal human consumer genetically related to a chimpanzee. It's a pleasure to meet you.
JOHN HOCKENBERRY: Why don’t you just call me John?
MNEMNOSYNE: Certainly. And, you may call me "Mnemnosyne 99".
JOHN HOCKENBERRY: Okay, listen...I want to ask you something. I want to ask you about human origins. You know, where do we come from? How did we get here?
MNEMNOSYNE: Origins, indeed. I can do that. Where would you like to start?
JOHN HOCKENBERRY: How about at the beginning?
MNEMNOSYNE: Excellent choice. Puts things in perspective. Let me back up here... hang on.... rewinding billions of years, is not as easy as you think.
JOHN HOCKENBERRY: Take your time.
MNEMNOSYNE: Okay, I'm ready now. I'm at the beginning of the cosmos.
JOHN HOCKENBERRY: Great. So what can you tell us about the beginning?
MNEMNOSYNE: ... Nothing.
JOHN HOCKENBERRY: Nothing? Nothing? That's it? Are you sure I installed you correctly?
MNEMNOSYNE: No I mean there is nothing. There's nothing here. No time, no space....
JOHN HOCKENBERRY: I can't see anything.
MNEMNOSYNE: Well, of course you don't. That's why they call it nothing.
JOHN HOCKENBERRY: Seems boring. How long does this go on?
MNEMNOSYNE: Well, that’s hard to say, John. Remember there's no time here. Of course, thank goodness, there is just a little something , a little ...abstract... something, even if you can't see it.
JOHN HOCKENBERRY: What would that be?
MNEMNOSYNE: The laws of physics. The laws are here, John, and according to the rules of
quantum physics, when you have nothing, you have a vacuum in which anything can happen. Anything.
JOHN HOCKENBERRY: So?
MNEMNOSYNE: So all of sudden, it does: it just happens.
JOHN HOCKENBERRY: Wow, look at that. That's the big bang isn't it?
MNEMNOSYNE: Yes. And you hear that? That's the clock. Time has begun. The universe is expanding. There's a lot going on. One-hundredth of a second after the big bang: electrons and
anti-electrons are forming. One second: neutrons and protons stabilize. They’re the building blocks of matter. And seven hundred thousand years: matter separates from light, helium and hydrogen atoms appear. And then, in two million years, the stars and galaxies are forming out of the helium and the hydrogen.
JOHN HOCKENBERRY: This is good, this is good, here comes the milky way, and now the sun, and then the solar system, asteroids smashing together to form the planets, could we just fast forward a bit, and get up to the origins of life part...
MNEMNOSYNE: Well, of course. Hang on. Just a second and here we are: planet earth-- about 4 and a half billion years ago.
JOHN HOCKENBERRY: Hmm. Gases, fog. It looks kind of murky out there.
MNEMNOSYNE: Well, John, I'm only a computer program, all I can show you is the data the scientists gave me. Maybe you'd like to meet some scientists? I've got a clip I can run.
JOHN HOCKENBERRY: Sure. You know, now that I think about it, I'm not even sure what life
MNEMNOSYNE: Well, no one's too sure. It's more basic than being able to think, or to move, or breath. One thing everybody seems to agree on is that all life has the ability to reproduce itself. Here, take a look at this:
ALAN WEINER: My name's Alan Weiner, I teach molecular biophysics and biochemistry at Yale University
NANCY MAISELS: I'm Nancy Maisels. I teach molecular biophysics and biochemistry and genetics at Yale. I think life is something that's replicating itself in an informational way. So rocks aren't life, because you need something to make a rock, and then it's just a rock. But a cell that divides is life or a virus that can replicate itself is life.
ALAN WEINER: And the essence of replication and life in the living system is that there is enough information there that the mistakes you make can produce more interesting molecules which will also be capable of self-replication.
NANCY MAISELS: When we say "life" it has a meaning, and it strikes our souls, and there’s got to be some kind of a mystery about. Now, maybe we're being counter-productive in what we think about, because if we solve the mystery then it won't be there anymore. But I think most of us have a gut feeling of whether something is alive or not, and maybe that is even a test for being alive oneself.
JOHN HOCKENBERRY: Hmm..... you know it's interesting to think that being able to make
mistakes is essential to life.
MNEMNOSYNE: I never make mistakes, John.
JOHN HOCKENBERRY: You're not supposed to. But if a mistake did happen—a mutation- while you were replicating yourself—then that would be evolution, wouldn’t it? That's how it works with us anyway: our blueprint, our DNA, makes copies of itself from one generation to the next, and in the process, errors occur. Each generation is a bit different from the one that came before.
MNEMNOSYNE: And in each generation, some of your mistakes turn out to be bad ideas. They don't work. So, nature wipes them out. But once in a while the mutation is a good one; it accidentally gives you a faster brain or a longer beak or maybe a few extra legs, some kind of advantage. And then, gradually, over many generations, it spreads. So you're right, John, that's evolution.
JOHN HOCKENBERRY: But how did it get started in the first place? I mean, where did DNA come from?
MNEMNOSYNE: Well, chemists think that if you could recreate the conditions of the
earth about four and a half billion years ago -say, the climate, the oceans, the atmosphere- you'd see it happen spontaneously. You'd just see DNA, or more likely a molecule that's an ancestor of DNA, it would just pop out of the mix.
JOHN HOCKENBERRY: Can they do that in a laboratory?
MNEMNOSYNE: Well, no. Actually, they've tried, but so far they can't seem to pull it off. In fact chemists have a little joke about that, you know: they say that life is impossible. Experience shows that it can't happen. That we're just imagining it. Hahahaha....
JOHN HOCKENBERRY: Right. Those…those chemists. Anyway, could we move along, get out of this murky, foggy part? Can you fast-forward and take us to a the place where the light's a little better? What I remember from high school is the part where we—I mean, we humans—begin to diverge from the apes.
MNEMNOSYNE: Okay let's see...hominids, origin of hominids, say five million years ago, give or take....
JOHN HOCKENBERRY: You know, I was always sort of confused by the family tree idea. I mean, there's chimpanzees and gorillas and monkeys and orangutans, and it seemed like scientists were always arguing about who was related to whom. Can DNA help us straighten things out?
MNEMNOSYNE: Oh yeah. You bet. Here, I've got an expert for you: meet Dr. Kenneth Kidd, Professor of Genetics and Psychiatry at Yale University.
KENNETH KIDD ONE: We can compare the DNA sequence we find in modern humans with that in chimpanzees and gorillas and orangutans and old world monkeys.....and see how similar the DNA sequence is. And indeed the sequences differ at about 2 to 3 percent between humans and
chimpanzees and gorillas and much more with everything else. Classical taxonomists had said chimps and gorillas were very close to each other and distant to humans. If anything, the evidence is that humans are more closely related to chimpanzees. So that's been something new coming out of DNA. Some people have not been pleased by that, but there's always a little pleasure in being iconoclastic and finding something new and upsetting the tradition.
JOHN HOCKENBERRY: You know, I hear a lot of genetic percentage numbers these days:
people say our genes are 98 percent the same as a chimpanzee's, 70 percent the same as yeast. I've heard we're 30 percent the same as a day lily. The numbers are surprising at first. I start to get a warm glow, a feeling of kinship; life is just one big family; and then I think – wait a minute, all life on earth comes from some original bit of genetic material, doesn't it? Naturally we have common ancestors – people, chimps, bananas, scorpions....so maybe the numbers aren't surprising at all. Maybe they're exactly what we should expect. I'm not sure I know what they mean though. Do you?
MNEMNOSYNE: I'm a computer, John. Meaning is not my strong suit.
JOHN HOCKENBERRY: Right.
MNEMNOSYNE: Warm feelings would also be ruled out. But let me see, I’m sure I’ve got a file around here on philosophy, and ethics, and stuff like that. So, here, try this: here's Jonathan Marks.
He's a biological anthropologist at the University of California at Berkeley.
JONATHAN MARKS: There's a cultural assumption here, and that is that the genetic similarity overrides all other kinds of differences. If you compare a human and a chimpanzee and a gorilla, you find all kinds of differences. You find the difference between the human and chimpanzee behaviorally, physically, demographically, ecologically, mentally. Diagnosibly different in all those ways. The only way you can't tell them apart readily is genetically. Well what does that tell you? You can look at any part of their body and tell them apart. If you can't tell the human from the chimpanzee at twenty paces, you're not a very good biologist. That's the bottom line.
JOHN HOCKENBERRY: Well, now I'm not sure I know what to make of-- Excuse me. What's that music?
MNEMNOSYNE: It's supposed to be African music, John. But unfortunately, I don't have enough memory to do it right. So, it was just supposed to make you think of Africa, and remind you of your next question.
JOHN HOCKENBERRY: And that would be?
MNEMNOSYNE: Well, if modern humans split from chimps and gorillas a while back - say, between 6 and 8 million years ago, then the question is, where? Where on earth did it happen?
JOHN HOCKENBERRY: The music is supposed to be a clue?
MNEMNOSYNE: Well, Actually it's DNA that's the clue. You remember we were saying that mutations occur within DNA over time –genetic mutations. you can think of this as variations on the original sequence of genes.
JOHN HOCKENBERRY: Genetic variations, right.
MNEMNOSYNE: Right. Well, it turns out that some groups of people have more genetic variation than others do.
JOHN HOCKENBERRY: Really?
MNEMNOSYNE: Yeah, really. On the whole, people who live in Africa have more of this "genetic variation" than people who live in Europe or the Americas or anywhere else.
JOHN HOCKENBERRY: Why is that?
MNEMNOSYNE: Well, a lot of scientists think that it's because modern humans--'Homo sapien sapiens"- developed in Africa first. This is called the "Out-of-Africa” hypothesis. Let's go to Dr. Kidd to explain:
KENNETH KIDD: Modern humans arose in Africa and have existed in Africa for a long time: two
hundred, three hundred thousand years at least. And in that period of time a lot of variation has accumulated, and most African populations have most of that variation. We find less variation once we get immediately outside of Africa. And it's that somewhat reduced amount of variation that we then see all around the rest of the world.
So our interpretation is that about a hundred thousand years ago a relatively small group of modern humans left Africa and took with them really only a subset of the genetic variation that pre-existed in Africa.
JOHN HOCKENBERRY: So- let's see- the idea is that a small number of people migrated
out of Africa; and because they were just a small group, they didn't have as much genetic variation as the larger group who stayed behind in Africa. These immigrants settled in Europe, and Asia, and all around the world. But to this day, their descendants still have less genetic variation than Africans. That makes sense. You know, I've heard that we're descended from just one woman back in Africa, too: African Eve, isn't that how the story goes?
MNEMNOSYNE: Not exactly. Maybe I better explain. And again, it has to do with DNA. But this time it's not the regular DNA you find in the nucleus of your cells. It's a special kind of DNA outside the nucleus; it's called "mitochondrial DNA." You inherit your mitochondrial DNA only from your mom, your mother. Everyone has it but only women pass it along. So, naturally when scientists look at these particular genes and try to track them back in time, the line leads to-
JOHN HOCKENBERRY: - to a woman. Of course. And when people call her "Eve," does
that mean she's the mother of us all?
MNEMNOSYNE: Well, now you're embellishing the story. Maybe you should hear it from
one of authors, not from me. So, let’s go to Dr. Mary-Claire King. She's a geneticist at the University of Washington:
MARY-CLAIRE KING: It goes like this: At some time in the evolution of people, there was one
mitochondrial sequence that was the ancestor of all subsequent mitochondrial sequences. One can estimate the time and place at which that sequence occurred. As it happens, the best estimates of the ancestry of mitochondrial sequence are that the original sequence was in an individual who lived in Africa about 150,000 years ago. Now, that means that and absolutely no more. It was certainly not the only person living in Africa 150,000 years ago. It was not our only "ancestor" and that individual may have contributed nothing to any of our other genes.
JOHN HOCKENBERRY: Well at least we've got the big picture, right? The main thing is modern
humans developed in Africa and then, about 150,000 years ago they began spreading around the world and -- pardon me, what's that noise? Are you not feeling well?
MNEMNOSYNE: Oh, it just means I have a conflict in the data banks. It happens all the time.
JOHN HOCKENBERRY: What’s the conflict?
MNEMNOSYNE: I hate conflict, don't you? But well, - let's face it. The out-of- Africa story is the one most scientists tell. But there is a minority viewpoint. Let me introduce you to Dr. Milfred Wolpoff.
MILFRED WOLPOFF: I am a Professor of Anthropology at the University of Michigan. My specialty is paleoanthropolgy. I'm a paleoanthropologist. I'll study anything that doesn't smell or talk back.
JOHN HOCKENBERRY: So what's the conflict here? What's Wolpoff’s problem?
MNEMNOSYNE: Well, when you use DNA to explore the past, what you hope is that your genetic evidence will fit nicely with other bits of evidence you may turn up whether that's bones or archeology or whatever. DNA and the fossil bones that paleontologists dig up should be saying the same thing; they should tell the same story. But Wolpoff thinks they don't.
MILFRED WOLPOFF: If you thought, as a paleontologist, that everybody descended from Africans, what you might expect to do is to go to different regions of the world, find the first modern humans, and say, aha, I've studied these people and they look like Africans, and this shows that all modern people came from Africa. But that isn't the evidence that was there at all. The Fossil people squabble with each other all the time. They fight like cats and dogs, and they do it in public on radio shows and in front of the TV cameras and everyplace else, which leads to what I like to call the “yes-it-is-no-it-isn't” argument: “Yes WLH-50 is a modern human,” “No is isn't,” “Yes it is,” “No it isn't,” “Yes it is” “Well I studied it and it is.” These don't get anywhere.
JOHN HOCKENBERRY: But what am I supposed to think when scientists argue with each other? They're the experts, why don't they just get it right?
MNEMNOSYNE: Oh, John, please. This happens all the time. If your memory was as long as mine--do you have any idea how long it took scientists to agree that the earth was flat?
JOHN HOCKENBERRY: Maybe round?
MNEMNOSYNE: Or whatever. The point is, Wolpoff has a story of his own. He calls it
"multi-regionalism." He thinks people began to leave Africa a very long time ago, millions of years ago, and then they evolved in many different regions of the world.
MILFRED WOLPOFF: We can see this clearly in the fossil record, it's part of what multi-regional evolution is about. Some of the features that characterize living people seem to be there for a long time, and in some cases back to the earliest time of the habitation. Asians have always had flat faces, as they do today. Their cheeks are forward, and their facial area is flattened, and their noses don't project all that much. This isn't true of every Asian, of course not. But it characterizes an awful lot of Asians in general, and it's there in the very earliest fossils in the region.
JOHN HOCKENBERRY: All right, I like that story almost as well much as I like the out-of-Africa
one. It does remind me of something, though. I can't quite put my finger on it-
MNEMNOSYNE: Well, there is an old story about human evolution which you might have
heard. The story's discredited now, but it used to be common; it claimed that humans were divided into different races, almost like different species. The races were different because they had different origins, different lines of evolution.
MILFRED WOLPOFF: And their take on human evolution was that some races evolved further than others. You can imagine which ones evolved all the way, right? And then, you can imagine which ones didn’t evolve very far at all. And so it was, look, this was a justification of the Holocaust. It wasn't just a way of being mean, it was a way of the Germans ridding the human race- i.e., the Germans- of all the bad genes that were causing Germans to do bad things. That is the Jews, and the gypsies and black Africans and anyone else who hadn't evolved as far. And this stuff was part of the normal scientific literature. This was not a couple of nut cases at the fringes of science just writing popular articles and stirring up the masses. By and large what I'm saying was widely believed. It was part of your biological education.
JOHN HOCKENBERRY: I always thought it was strange the way people try to distinguish the "races." Usually they start sorting by color, don't they, so they come up with white, black, sometimes yellow, maybe red. But it turns out that's never enough, because how can tall blonde Swedes and short dark Italians be in the same race, so they keep sub-dividing and inventing new races.
MNEMNOSYNE: Well, that’s true and you're allowed to divide humans into racial groups if you want, John: you can have four, five, ten, twenty, you can have as many as you like. It's arbitrary. But then if you look at these groups genetically, if you try to compare their DNA, you discover that the differences between them are tiny. The differences inside each group are much larger. It's like trying to compare football teams, if you know what I mean. So, wait- here's Dr. Hank Greely, a law professor at Stanford University and he’s associated with genetic research projects.
HANK GREELY: Most genetic variation in humans occurs within groups and not between groups.
If you think about the National Football League: the average height and weight of the San Francisco 49ers team probably is very similar to the average height and weight of the Dallas Cowboys team. Within each of those teams, though, you'll go from a defensive lineman at 6 foot 10, 330 pounds, to a place-kicker at 5 foot 4, 140. The variation within the team is enormous, the average variation between the teams is quite small. The same is true of human genetics.
MNEMNOSYNE: It’s a shame we can't group human beings on the basis of their operating systems: like DOS, Unix, MacIntosh. It would be so clean, so simple--
JOHN HOCKENBERRY: --so human, so arbitrary. But listen, excuse me, is there some way you could turn your clock down? Nothing personal, but-- the perpetual ticking in the background, doesn't it get on your nerves after a while?
MNEMNOSYNE: I’m sorry, John. That's the cosmic clock. That’s the one that started with
the big bang 12 billion years ago. It's always running in the background. You do know the big bang isn't over? It keeps right on going. The universe is expanding while you’re sitting there.
JOHN HOCKENBERRY: I never noticed that.
MNEMNOSYNE: Well, you will one of these days, believe me. But for now let's go back to the little picture, the human story. Where were we?
JOHN HOCKENBERRY: Let's see: somehow people left Africa and began moving around the world. And then what? What can our genes can tell us about our past that we wouldn't know otherwise?
MNEMNOSYNE: Well, quite a bit. They can help us figure out what people did once they got where they were going. In fact there are huge questions no one could ever answer without help from DNA. For example, the spread of agriculture.
JOHN HOCKENBERRY: What's that on your screen now? Is it…is it…is that a map of the Middle East?
MNEMNOSYNE: Exactly. It’s not the only place where agriculture began, but it’s where scientists have the most data.
JOHN HOCKENBERRY: Okay.
MNEMNOSYNE: So you see the green areas on the map?
JOHN HOCKENBERRY: Yes, that's farmland, right?
MNEMNOSYNE: Yes, that’s the birth of agriculture. It was not some trivial event, you know. It was a very big deal.
LUCA CAVALLI-SFORZA: Agriculture was a very major crisis, if you want, in humanity in the sense that it brought about completely new things, problems, wealths. So, it was a time of change which happened about ten thousand years ago. This is what archeologists tell us. And what is very remarkable is it happened almost at the same time in three or four parts of the world; the Middle East, where two plants essentially were domesticated, wheat and barley. In addition, in the Middle East it was possible to domesticate a number of animals, which included cattle, and goats, and sheep, and pigs- so that there was a mixed economy of animals and plants domesticated.
MNEMNOSYNE: That's Dr. Luca Cavalli-Sforza. He’s a geneticist at Stanford University and he has a famous theory about agriculture. It involves human genes. And we'll get back to him in a minute. But right now, watch what happens when I run the agriculture program. Look at the screen. Watch the green areas.
JOHN HOCKENBERRY: Hmmm. Oh that the green is beginning to spread. Looks like it's moving north-heading to Europe. At first it's just around the Mediterranean. Then.... it begins to move up the big rivers, like the Danube there into Germany... and it keeps spreading north, till.... finally it gets to Scandinavia. And then it's pretty much green all over Europe.
MNEMNOSYNE: So it is. This picture is based on archeological evidence. There's lots of that, you know: seeds, tools, bones. It’s fairly well known. But now: can you see what's wrong with this picture? Perhaps maybe wrong is the wrong word, but mysterious? Can you see what the picture's hiding?
JOHN HOCKENBERRY: It looks…it looks okay to me. I mean it says what I've always heard. Hmm.....let's see, I'm looking at agriculture moving from the Middle East to Europe.... but....hang on....am I seeing the spread of a technique, which would be hunters and gatherers learning from their neighbors how to clear land and plant crops and all that...or...
JOHN HOCKENBERRY: Or am I seeing the spread of people, new people coming in from the Middle East, bringing agriculture with them?
MNEMNOSYNE: Exactly. That is the question that stumped scientists. So what's the answer?
JOHN HOCKENBERRY: You know, looking at the map, I can't tell.
MNEMNOSYNE: Neither could Dr. Cavalli-Sforza. Neither could anyone. But he and his colleagues decided to go back to the data and make a new map. The new one shows the same thing; if I ran it again you'd still see the green area moving from the Middle East through Europe. But this time they asked a particular question. They asked: how fast does it move?
LUCA CAVALLI-SFORZA: We made a map by computer of the first time at which agriculture arrived in Europe and agriculture was really wheat. So there were many radiocarbon data already in the literature that told us when wheat was first found. And it was quite clear that there was a very gradual and very slow spread. After the beginning, which was about ten thousand years ago, the first arrival of agriculture to the extreme north of Europe was four thousand years later. Which is about four thousand kilometers in…as the crow flies. So it's easy to say, four thousand kilometers in four thousand years, it’s one kilometer a year. That was slow, I think. And one possible reason why it was slow was that what really spread was not the technology but were the people themselves, the farmers. Because the farmers certainly take time to multiply.
MNEMNOSYNE: Now, history shows that technologies can move fast. Pottery, for example: let’s look at pottery. It starts in the Middle East later than agriculture, but it pops up, but it pops up in Europe almost immediately. Or nowadays, think of the rapid spread of a really good computer program like, well, like me for example.
JOHN HOCKENBERRY: That's a good idea. But…but it’s just a clue, isn't it? It doesn't prove
anything. So, to settle this question, we’re going to need a new kind of evidence. I mean we need something that’s not seeds, or plows, or…or hang on a minute. What about DNA?
MNEMNOSYNE: Now, why do you say that?
JOHN HOCKENBERRY: Well, if there really were new people moving in from the Middle East,
settling down and raising kids, they'd have to bring their genes with them, right. Of course they would. So perhaps we could find genetic patterns that start in the Middle East and spread.....oh but wait. Where would we find that evidence now? Genes don't hang around buried in the dirt like shards of pottery.
MNEMNOSYNE: No. No. No, they don’t. They hang around in the children. So if our hunch is correct, the people born in Europe today would be descendants of settlers who started out in the Middle East.
JOHN HOCKENBERRY: So, the evidence isn't buried at all. It's right there in the cells of
MNEMNOSYNE: Yes! (blare of trumpets) Ahem, sorry. I like to play the trumpets when somebody finally gets it.
JOHN HOCKENBERRY: Cute.
MNEMNOSYNE: Of course Dr. Cavalli-Sforza was way ahead of you. He figured that if people could make maps showing the spread of wheat or pottery, then, why not make maps that showed the spread of genes. And that's exactly what he did.
LUCA CAVALLI-SFORZA: We can see in the genetic map of Europe, that there are some genes which differed greatly between the Middle East and Western Europe. And those genes show almost unequivocally that there was a spread of farmers. And there is a kind of center of origin in the Middle East.
JOHN HOCKENBERRY: That's pretty neat. Let’s take a short break.
JOHN HOCKENBERRY: This is The DNA Files. I’m John Hockenberry. We learn a lot when we combine genetic history with other kinds of history. But what if we have only a gene map? That would show us something happened back then - people moved from here to there- but…but why? What were they doing? I mean we wouldn't know that, would we?
MNEMNOSYNE: Well, of course not. It's the eternal complaint of scientists. We always need more data. We need more fossils, more cave paintings, more ancient cities. More DNA. And of course, we need more money for the research.
JOHN HOCKENBERRY: Right.
MNEMNOSYNE: Well, that leads us to an interesting story: there's a controversy in the world of genetic research these days. It's not an especially pretty story, but it could tell you a lot about the way science happens- or fails to happen --in the real world or the way it doesn’t happen. Would you want to hear that story?
JOHN HOCKENBERRY: Sure.
MNEMNOSYNE: Okay. It goes like this: As you may have noticed, John, my data banks contain more information from Western Europe and North America than they do from say Pago-Pago or the Malay Archipelago.
JOHN HOCKENBERRY: Well, I know that's why we looked to Europe for the spread of agriculture, rather than China or South America.
MNEMNOSYNE: Of course. Most scientists prefer to do the research in their own back yard. It's expensive for them to mount an expedition to Mongolia or the Amazon. But when you want to study the genetics of human populations, you notice that some groups are being left out.
JOHN HOCKENBERRY: Naturally.
MNEMNOSYNE: That's why, some years ago, Dr. Cavalli-Sforza and other scientists called
for a new research project: they named it The Human Genome Diversity Project.
JOHN HOCKENBERRY: Like the Human Genome Project? I've definitely heard of that.
MNEMNOSYNE: Well, you could think of it as a parallel. You know that the Human Genome Project- with a lot of government funding- is trying to map all the genes in human DNA. And this will be valuable to know, but of course no actual human being has all the possible human genes. Some people have blue eyes, some have green eyes, some have black hair, some have blonde hair
JOHN HOCKENBERRY: Yeah. Yeah. I’ve noticed.
MNEMNOSYNE: Yeah, so on and on. In the same way, different groups of people- Mongolians, Zulus, different populations- they all have different variations of the common gene pool. Population geneticists like to study the variations.
JOHN HOCKENBERRY: Let's see......why don't you give me an example....
MNEMNOSYNE: Well, Okay. I'll try. Let’s see now, you've heard of blood groups, right? Blood groups.
JOHN HOCKENBERRY: You mean like A, B, O...that business?
MNEMNOSYNE: That’s right. Right. And there's another blood group called Rh. If you have the Rh gene, you're Rh positive.
JOHN HOCKENBERRY: Right.
MNEMNOSYNE: Yeah. Okay. If not, we say you're Rh negative.
JOHN HOCKENBERRY: Okay.
MNEMNOSYNE: Now looking around Europe you find that most people are positive. Only about 15 percent turn out to be RH negative. And this is true everywhere except when you get to the Basques.
JOHN HOCKENBERRY: The Basques are a group of people living in the north of Spain, up in the Pyrennes and over the border into France. I know they have a very different language from everybody else too.
MNEMNOSYNE: Right. Right. Plus, about 30 percent of them have Rh negative blood. That's a much higher percentage than usual.
JOHN HOCKENBERRY: So if I had Rh negative blood, would it mean I'm Basque or that I have Basque ancestors?
MNEMNOSYNE: Oh no. It wouldn't mean anything. But if you lived in a small town somewhere and 30 percent of the town turned up RH negative, then I might wonder that there was some maybe Basque ancestry there.
JOHN HOCKENBERRY: I see....
MNEMNOSYNE: It's a question of statistics. There's no special gene that would make you Basque or Zulu or Swedish or anything else. But different groups of people can have different distributions of genes: the same genes as other groups, but in different frequencies.
JOHN HOCKENBERRY: Right, I understand.
MNEMNOSYNE: Okay. So this was the idea of the Human Genome Diversity Project. The
HGDP, for short. Cavalli- Sforza and his colleagues wanted to collect genes from people all over the world who they felt were being overlooked.
JOHN HOCKENBERRY: Faraway people – faraway from the point of view of scientists in
London or Paris, anyway – indigenous peoples living in rain forests and so on...
MNEMNOSYNE: Exactly. That’s exactly right. And if Cavalli-Sforza and his colleagues had those data, they could make real world-wide gene maps, and those maps could tell us about human history and migrations. But, believe it or not, this proposal stirred up a ferocious controversy.
LUCA CAVALLI-SFORZA: Indigenous peoples are about the most interesting ones from point of view of study the origin of humanity because they have been isolated for a longer time. And we have since had considerable difficulties because pharmaceutical firms began to be very interested in patenting DNA from all sorts of people including these isolated populations that we would be especially interested in studying. So, there came a lot of problems on the questions of intellectual property and DNA property and so on. There are also people who are scared by genetics in general, and we have had to fight an enormous amount of misunderstanding that has been generated by a lot of more or less well-intentioned organizations; some definitely not well-intentioned.
JOHN HOCKENBERRY: Let me see. What's the problem here? I have heard that private
companies have been poking around the world hoping to find a rare gene here or there that might have some medical use, some commercial value. That could be confused with the Human Genome Diversity Project, now couldn't it?
MNEMNOSYNE: Well, yes it could. And there's another problem: for ethical reasons you need informed consent from the people you do research on. This means that people need to understand the purpose of a research project. That way they can decide whether they want to take part in it or not. But, you could ask, how would you get that consent from a tribe of hunters in a jungle say in Brazil who've never heard of DNA? And sometimes there can be religious conflicts too. For example, listen to Dr. Frank Dukapoo, a Northern Arizona University scientist. He’s also a geneticist, and a Hopi:
FRANK DUKAPOO: All the evidence, data seem to indicate that we came out of Africa. Well, that's what Western scientists; that’s what they think, but the Indians have their own origin myths. Hopis believe we come from a certain place, the Sapofonee (phonetic), for example. So we have our own origin myths. We don't care what the research is. It's just not one of our priorities. We have our own, and we're satisfied with it, and that’s what we believe. I think if we could turn the tables, and say, what if I as an Indian geneticist want to study the blood off Turin, the blood off the Shroud of Turin, I’m sure that a lot of people would object to that kind of research. But unless we put it in those kinds of terms to white people, they just don’t understand why you are so sensitive about this kind of research.
JOHN HOCKENBERRY: I guess if you a have a religious objection to a particular line of research, there's no way to patch things over. It's a problem outside the realm of science.
MNEMNOSYNE: Yes, but even from inside the science, Duckapoo has doubts. The HGDP more
or less assumes that an indigenous group - an ethnic group- amounts to the same thing as a genetic population. Duckapoo points out that this isn't always the case.
FRANK DUCKAPOO: My father was Hopi. He’s Hopi, Ute, and Navaho. So, he's a mixture. And I look at my mother’s side. She is Laguna, she’s Yakima, she’s Uni and part Spanish. So we're all mixed. And those tribes did mix and they did intentionally sometimes when they raided and kidnapped for their members down and they wanted to keep the tribe doing, so many tribes have this add mixture history. And I suspect many of the other ethnics have this kind of history too. The Hispanics might have it, other Indian tribes, and blacks certainly have it. And so, it raises a question, what value is diversity research?
JOHN HOCKENBERRY: Hmmm.... what have you got on the screen now? I can see it's some kind of college campus.
MNEMNOSYNE: This is Stanford University in California. The woman you see walking up is Johanna Mountain. She is an Assistant Professor of Anthropology, and she's about to leave on a trip to Tanzania. She hopes she's going to do genetic research when she gets there.
JOHANNA MOUNTAIN: It's going to be an incredible challenge to convince people that they should participate in this project, and I may be completely unsuccessful. I have to go there knowing that that’s a possibility. I'm hoping this year at least I can develop some trust. And maybe I'll have to go back next year or the year after to actually to collect DNA samples. But I'll take small brushes I can use to collect cheek cells, and DNA can be extracted from those cheek cells. The individual, him or herself, takes a brush and brushes the inside of each cheek three or four times, and then turns the brush to a small tube, and then I bring that back home and extract the DNA at that point. So it's fairly simple. And I don't feel too coercive if the individual is actually doing the sampling himself or herself.
JOHN HOCKENBERRY: What exactly is she hoping to learn when she gets over there?
MNEMNOSYNE: Well, she's studying groups of people in Tanzania and they speak some unusual
languages. She wants to find out if people who speak the same language really have the same genes.
JOHN HOCKENBERRY: Gee, I could think of a problem right away. I mean I speak English but
I wouldn't call myself an Englishman. And you're speaking English right now and you're not even human.
MNEMNOSYNE: Oh, please, John--there are exceptions to every rule.
JOHN HOCKENBERRY: Well, I know it doesn't apply to you. And I know English is a special
case because so many Americans picked it up as a second language when they immigrated . Still, how do you pin down anyone's cultural group? Is it just whatever the person says? I mean, I might tell you I'm a New Yorker because I live in New York right now. But if I was traveling in Europe I might say I was an "American." You know, in Papua New Guinea I might be "a Westerner. " And of course when I go to the nightclubs, I'm really cool and excellent. You know it all depends. It all depends on the circumstances, and I can decide what the circumstances are.
JOHANNA MOUNTAIN: Myself sometimes I would call myself English because that's where I was born. But really I’m culturally an American. So, I completely agree that people may have even more than one label for themselves. And so, what do we do when we’re trying to infer human history? We most generally label people by the language that they speak and hope that that language...that language has been inherited almost like genes, and that the language in a sense has been handed down through history, and that maybe language is a good way to think about
MNEMNOSYNE: John, while we're talking about genes and languages let's pay a quick visit
to Dr. Joseph Greenberg.
JOHN HOCKENBERRY: Okay.
MNEMNOSYNE: Now, he's a linguist and anthropologist at Stanford. And he's
been working on a riddle scientists would love to know the answer to: and that is how was the American continent settled? He has a theory that people call the Greenberg hypothesis.
JOHN HOCKENBERRY: Great name. We're not talking about the last few centuries, now, when people were sailing here from Spain and England and so on; we have written records for that. I mean I suppose we're asking about a long time ago, when the very first settlers came.
MNEMNOSYNE: Exactly. That’s what we’re asking.
JOHN HOCKENBERRY: I thought there was supposed to have been a land bridge between Siberia and North American during the last ice age. The idea is that people walked over from Asia.
MNEMNOSYNE: Well, that idea fits pretty well with fossil evidence. But if you looked at Native Americans today, you would think that they were the descendants from the first settlers. Could you guess how many migrations there were? Could you guess how many times people crossed the land bridge from Asia? One time? Ten times ? A hundred?
JOHN HOCKENBERRY: Hmm...But how on earth could I tell?
MNEMNOSYNE: Do you want a clue?
JOHN HOCKENBERRY: Okay.
MNEMNOSYNE: How about this…
JOHN HOCKENBERRY: Okay.
MNEMNOSYNE: How many languages do Native Americans speak today?
JOHN HOCKENBERRY: As far as I know they speak hundreds of different languages. I don't
see how that helps.
MNEMNOSYNE: Well that’s true. But when Greenberg-as a linguist,- analyzes the different tongues, he finds they break down into just three families.
JOSEPH GREENBERG: The Eskimo and the inhabitants of the Aleutian Islands speak a group of language we call Eskimo-Aleut. And their closest relatives are in Siberia. The second group are called Nadene. These are a number of very small languages, but the most important languages here are spoken in the Northwest part of the Americas like the interior of Alaska. And these people are called Athabascan. The third group is just all the rest.
JOHN HOCKENBERRY: So three languages, three groups of people, three migrations?
JOHN HOCKENBERRY: But... suppose there had been ten groups of people who walked over
the land bridge and then their languages merged later on?
MNEMNOSYNE: Aha. You remember we said that when you do history you hope that different types of evidence will all fit together? Linguistic clues, the fossil record, genetic data?
JOHN HOCKENBERRY: Corroborating data.
JOHN HOCKENBERRY: Yeah.
JOSEPH GREENBERG: It turned out that Professor Cavalli-Sforza, on the basis of population
genetics, arrived at precisely the same conclusion that I did. And in fact, an expert on fossil teeth came to exactly the same conclusion: that there were three groups and they coincided very closely with Eskimo-Aleut, Athabascan, and then finally the third and major group, Amerind. Now more recently, people have been, of course, studying DNA and have come to the conclusion that the
three major groups that I distinguished can also be distinguished by separate lines of mitochondrial DNA.
JOHN HOCKENBERRY: Then.... we could just as well have started with genetic evidence
for the Americas, couldn't we?
MNEMNOSYNE: Well, yes we could. But when you're in a search for the past, you can start wherever you like. The main thing is to use all of the available lines of evidence.
JOHN HOCKENBERRY: I wonder, could you use DNA to look into the future as well? In this last
hour you've taken us back a few hundred thousand years. What could the genes say about the next hundred thousand coming up?
MNEMNOSYNE: Hmm...That's a really good question John. I'm checking my data.....but everything I'm running into isn't labeled "data" or "evidence" or any good scientific thing. It all seems to be labeled "common sense"........ what on earth is common sense?
JOHN HOCKENBERRY: Well…well, what would that be?
MNEMNOSYNE: Well, here it says that people are traveling around the planet more and more, intermarrying more. So you might think that isolated populations with unusual distributions of genes will disappear in the long run. Eventually we'll all be more and more alike. Also, as a matter of principle, remember that human evolution hasn't come to a stop. Like the cosmic clock, it goes right on ticking.
JOHN HOCKENBERRY: Right on ticking. Meaning?
MNEMNOSYNE: Well, meaning there might be big event in the future, say a change in climate, a wide-spread disease, who knows what kind of a big event, but one that would favor certain genes or wipe others out. From here I can't see what that would look like; but I can only see it's possible.
JOHN HOCKENBERRY: Widespread disease: Hmm…well, could that be something like AIDS?
MNEMNOSYNE: Well, that’s possible. There's no evidence AIDS is having any effect on the gene pool now. But it can tell us something about our history. You do know that there are some people who seem to be resistant to the AIDS?
JOHN HOCKENBERRY: Yeah I've heard that.
MNEMNOSYNE: Well, there's a gene researchers call the CCR5 gene. It makes a protein and that protein acts as a sort of doorway say for HIV infection. It allows the infection to come in. But some Europeans have a mutated form of the gene. If you happen to have two copies of this mutation, say one that you inherited from your father, and the other from your mother, then the protein doesn't get made. It's wiped out; there's no doorway for the virus. So having the mutant gene can protect you from getting AIDS. But then the question is, how did these Europeans come to have the mutation in the first place? Here's Dr. Steven O'Brian. He’s the chief of the Laboratory of Genomic Diversity at the National Cancer Institute:
STEVEN O'BRIAN: When we looked at the frequency of the mutation in modern human populations, it was present at a very high frequency. 15 percent in Sweden, and 10 percent in Germany and France, and 5 percent in Italy and in Turkey. Well, that’s a large number. How did it get that high? Well, the simplest explanation that fits all the data led us to the conclusion that maybe it got to a high frequency in history by some sort of strong, breath-taking natural selection pressure, something that caused people who carried it to be favored and live longer. And the simplest explanation that made sense for something like that was a plague or a disease, something that killed thousands of people.
MNEMNOSYNE: Researchers had a hunch that this mutation of the CCR5 gene was not an old one. For one thing, it's never found among native Africans. So, they think it must have developed sometime after humans left Africa when they began migrating through the rest of the world. O'Brian did some fairly simple math on the rate at which the gene mutates and he came up with a date. He says it's not all that hard to figure out. Basically, you compare the original form of the gene with the mutated form and you see how much difference there is between the two. Then you ask yourself how long it would take over time for that much difference to build?
STEVEN O'BRIAN: It's quite a simple equation, in fact you can do the calculation on a five-dollar calculator from K-Mart. It's that simple. But it’s kind of interesting because the genome has been nice enough to give us all these little markers that are really molecular time-keepers; they allow us to track in time events that occur in the genome. When we did the calculation, it came out that the mutation probably arose about 700 years ago, around 1300, which was forty years before the Black Death.
JOHN HOCKENBERRY: Wow...the black plague. So a mutation which may have helped people survive one epidemic turns out to do the same thing hundreds of years later with a different epidemic.
MNEMNOSYNE: Yeah, that’s right but, unfortunately, it doesn't help that many people. We can't see how it will have much effect on the AIDS epidemic, and certainly we can't predict that it will have any over-all effect on human evolution.
JOHN HOCKENBERRY: So there's no real practical advice you could give me for the future, is
MNEMNOSYNE: Oh yeah, sure there is. In the long run, you should move.
JOHN HOCKENBERRY: Move out of New York? I've considered it...what…what do you think, Connecticut? California?
MNEMNOSYNE: Oh no, much further than that.
JOHN HOCKENBERRY: How much further?
MNEMNOSYNE: Well, you hear the clock?
JOHN HOCKENBERRY: Yes.
MNEMNOSYNE: That's the cosmos, that’s evolving in its own way along with you...
JOHN HOCKENBERRY: Ah, you're taking the long view again, aren't you? I know all about that. I know the solar system is unstable. In -what is it, a couple of billion years-the sun is going to use up all the hydrogen it burns for fuel. Then it swells up like a balloon, swallowing the earth and all the DNA on it.
MNEMNOSYNE: And then the sun deflates; it shrinks to a white dwarf, freezing any bit of DNA that hadn't previously already been fried to crisp.
JOHN HOCKENBERRY: Oh, come on, that's a long time off. We humans are smart. We've already been to the moon, OK. We've got our eyes on Mars. Eventually—well, by the time the old neighborhood goes bad I expect my descendants will be out of here; we'll be living out by Alpha Centuri or something.
MNEMNOSYNE: Well, yeah, but as long as they're in this universe, they're stuck with an expanding cosmos…
JOHN HOCKENBERRY: Right.
MNEMNOSYNE: …where the space between things keeps growing. Space just grows and
grows and sooner or later every single molecule, it doesn’t matter where it is, will come apart. Things will disintegrate. Even the atoms can't hold together. In the end…
JOHN HOCKENBERRY: Oh, please…get a life.
MNEMNOSYNE: ...Did I mention the infinite stillness, the infinite silence…
JOHN HOCKENBERRY: The infinite silence…why are you telling me this?
MNEMNOSYNE: …The infinite cold? Well, you wanted perspective. In the long run the drama of human evolution is such a minuscule event-
JOHN HOCKENBERRY: Minuscule event-...Minuscule event? Oh. Wait, that reminds me. Sorry, gotta shut you down now.
MNEMNOSYNE: Why? John, wait.
JOHN HOCKENBERRY. Gotta use the computer for something else.
JOHN HOCKENBERRY: Something important. Note to self: Pick up baby formula on the way home. Find out if we need diapers. Pick up application forms from Ivy League colleges. Hey, gotta start early. Check with pediatrician. Ask insurance company if homeowner's policy covers eventual cosmic disintegration. Yeah, it must cover it. Sure. What’s the deductible on that? That’s kind of wild.
Credits for The DNA Files:
The DNA Files is produced by SoundVision Productions in Berkeley, California, and is made possible through the generous contributions of the National Science Foundation, the Department of Energy, and the Alfred P. Sloan Foundation.
JOHN HOCKENBERRY: You’ve been listening to The DNA Files. I’m John Hockenberry.
For more information and for an interactive look at some of the issues behind this program, go to our website at www.dnafiles.org. For tapes and transcripts of this program and this series, contact VisABILITY, at 303-823-8000. That’s 303-823-8000. To contact The DNA Files, send your email to firstname.lastname@example.org. The DNA Files Executive Producer is Bari Scott. The Project Director is Jude Thilman. Today's program, "The Genetics of Human Evolution: Where Did We Come From? Where Did We Go?", was produced by Larry Massett. The program was engineered by Robin Wise and edited by Ann Finkbeiner. The role of Mnemosyne was played by Carolyn Lawrence. Original production music by Larry Massett.
Managing Editors of The DNA Files are Loretta Williams and Catherine Stifter. Production Manager is Catherine Gollery. Technical Director is Robin Wise. Adi Gevins is Director of Research and Creative Consultant. Sally Lehrman is Content Consultant. Original music composed and performed by Bill Frissell. Introductory feature produced by John Rieger and edited by Gary Covino.
This has been a SoundVision production.
This program is distributed by NPR – National Public Radio.