'Before the Dawn' Author Nicholas Wade

Reporter Nicholas Wade talks about how DNA analysis is rewriting our recent — and ancient — history, including a better understanding the evolution of humans. His new book is Before the Dawn: Recovering The Lost History of Our Ancestors.

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IRA FLATOW, host:

For the rest of the hour we're going to turn to evolution. Last month several researchers announced what they say is proof positive that we humans are still evolving. They scanned the human genome and found 700 genes that have appear to have responded to the pressure of natural selection within the last 10,000 years. Now that doesn't sound like, sounds like a long time, but, you know, it's a flip on the radar screen in terms of evolutionary history.

And there's some of the more interesting genes. Genes that allow us to digest lactose as adults, genes that influence skin color, bone structure. Now this news may surprise you, if you're one of many of us accustomed to thinking about evolution as a thing of the past or something that happens to other animals, not to us. But I'll bet my next guest was not-at-all surprised by this study.

He's written a book that makes the case that genetics is the backbone underlying every major evolutionary advance in our history and prehistory. That our genes hold a story that our evolution from apes to humans, our migration out of Africa and around the globe, our transition from hunter-gatherers to more complex societies, and our development of language and complex behaviors. This hour we're going to be talking about how DNA is re-writing our history, how evolution is still happening today, about the future evolution of human species. Could our human population one day become distinct species.

A lot to talk about, if you'd like to join in. Our number is 1-800-989-8255. Nicholas Wade is the author of BEFORE THE DAWN: RECOVERING THE LOST HISTORY OF OUR ANCESTORS, out this month from Penguin Press. Science reporter from The New York Times, here in New York, been a science reporter for decades, as long as I've been doing this, if not longer. He joins me here in our NPR studios. Welcome back to the program, Nick.

Mr. NICHOLAS WADE (Author, "Before The Dawn"): Thanks Ira.

FLATOW: What made you want to write this book, BEFORE THE DAWN? That's a typical question you ask of an author, but I know you do specialize in this field.

Mr. WADE: Well I, I found I was writing many stories about genetics, growing a human genome that was sequenced just three years ago, 2003, and many of them looks into dark corners of the human past that we, had been inaccessible before then. And I conceived the idea of writing this book focused on the most recent 50,000 years of our history. There are many books about fossil skulls and stone tools, and those end about 100,000 years ago. But 50,000 years ago I think is where it really starts to get interesting. That's when the ancestral human population lived. And many of these new genetic findings help explain aspects of our past that we would never have known about, otherwise. So in the book I've tried to weave together all the traditional disagreements that bear on the human past, archeology, paleo-anthropology, historical linguistics, with the thread of genetics as the common theme.

FLATOW: Do we actually carry with us all that history, going back 50/100 thousand years?

Mr. WADE: Well, we do, it's all in our genealogy and it's very ancient. It's changing all the time, but it has an ancient pedigree.

FLATOW: Uh huh. And how does that show up. How is it carried? You talk very interestingly about the y chromosome and the mitochondrial DNA, and how that's passed down. I thought that was fascinating. Explain that to us.

Mr. WADE: Well, the Y chromosome is a wonderful way of tracking our migrations across the globe from our ancestral homeland somewhere in northeast Africa, probably around Ethiopia. And the reason that is, is two-fold. First is, very surprisingly, everyone, every man carries the same y chromosome inherited from some genetic Adam who lived in the ancestral human population. Of course there are about 2,000 men in that early population but only one Y chromosome survived. And it's weird because in each generation, some men will have either daughters or no children. So their Y chromosomes will get extinct.

And in the small population, one gene or chromosome, whatever, will substitute for the others.

But the second reason is that although it's the same chromosome that all us men carry, mutations have built up on it generation by generation. And you can use these mutations to sort of create a tree and assign each man to a branch. And these branches still bear the geographical pattern of how we spread across the globe.

FLATOW: And as far as the female side?

Mr. WADE: Right. I should have mentioned, the Y chromosome is not shuffled between generations like all the rest of the genes. So that makes it very easy to track.

And there's one other part of the genome that doesn't get shuffled and that is the mitochondrial DNA which comes just through the mother because the sperm's mitochondria are destroyed when it fertilizes the egg. So only the mothers prevail.

FLATOW: One of the surprising things about the history of this, the following the DNAs, how the DNA evidence fits with the timeline of human evolution. It comes from the fossil evidence. How good a fit is it? And how do we know it's such a good fit?

Mr. WADE: Well, I think, I mean, it's what I regard as a forced fit because the genetic dates are very interesting. And they got it in a relative sense. They tell you A comes before B. But you should distrust the numbers that the geneticist put out when they say, well, mitochondrial E lived 128,000 years ago.

Yes, but it's give or take 50,000 years either way. So for really good dates, you know, it needs to go to the archaeology. And the carbon 14 dates are solid. You can go to the bank with them.

So I think one takes the relative -- if you've got a genetic tree of whatever, the Y chromosome and going across the world, their are branch points on it, each of which can be taken in a relative sense. But for an absolute date, you just need to fix one branch with an archaeological date and that allows you to read off all the others in the relative terms.

FLATOW: Does the DNA fit more gaps than the fossil record does?

Mr. WADE: Well, it does in a sense in that the fossil record is inherently gappy but the genetic record is sort of complete and continuous. So you can get a fix on any gene you want simply by sampling enough genes in today's population and working backwards from those to whatever period you're interested in.

FLATOW: One of the biggest puzzles that we always talk about in evolution is at what joint, what point the ancestors of humans and chimps, where were they joint that they came from? Can DNA evidence provide any answers to that?

Mr. WADE: Well, it can because we have no fossils in that critical period when we and the chimps started to split apart…

FLATOW: Right.

Mr. WADE: …from our common ancestors. But you can draw up a genetic, a tree, if you look at the DNA of us and all the great apes. And that gives you a tree.

And the part of it you can date very well is when the orangutans branched off from the African apes. And with that date, which I think is like 12 million years ago, you can say, well, chimps and humans must have parted company about five million years ago.

FLATOW: Talking with Nicholas Wade, author of Before the Dawn: Recovering the Lost History of Our Ancestors, on TALK OF THE NATION: SCIENCE FRIDAY from NPR News. I'm Ira Flatow.

If we all have the, all we men, have the same Y chromosome from that one person 50,000 years ago, why do we all look so different and act so different, you know? What happened there?

Mr. WADE: Well, I think the answer there, you get into the previously murky subject of the genetic basis of race. So there's been what I would call a conspiracy of silence on this.

The geneticists have not really wanted to say much about it, for good reason. They really didn't know very much until recently. The social scientists have much preferred to say, well, race is a social construct. It's not biological. There's nothing genetic there. And we're all, all diversity is cultural.

So everyone's been sort of happy with that position. And there are good sort of historical reasons why we've taken that course.

But now that the geneticists are beginning to understand the genetic differentiation of the human population. And it's so simply that 50,000 years ago there was one tiny human family, a mere 5,000 people, about that. There was -- they all interbred with each other, all each other's cousins. We all looked exactly alike.

But as soon as we spread out from Africa and started to live on the far-flung continents around the world, there was no longer any intermixing. Now, the genome doesn't stand still. It's mutating all the time.

So this meant that on each continent, each population started to evolve independently to all the others. And to respond to the local environmental stresses, whatever those were. It's hardly surprising that we do differ from each other in certain ways. We differ in sort of skin and hair color and skeleton, the obvious ways. Maybe we differ in other ways, behavioral ways, but we've yet to identify.

It seems -- if you look at the genes that underly this, these are genes that have been selected for -- I should mention that there's kinds of change that go on in the genome. One is what geneticists call mutual evolution, the changes in the DNA that don't do any, don't make any difference, evolution doesn't care about them. And these are mutual genes.

Most change is mutual. Only a very few changes are selected. In other words, nature has made them more common because they do something. And it looks like from the Pritchard(ph) paper you were describing just now, there are just probably quite a limited number of genes, maybe still 200 in each of the main continental races, that have been under selective pressure.

And it's these genes that have probably driven the differentiation of the human species.

FLATOW: In such a short period of time, such a great change.

Mr. WADE: Yes. In a way it's not surprising because there was enormous change from 100,000 years ago, when we first took our present shape, to 50,000 years ago…

FLATOW: Right.

Mr. WADE: …so 50,000 year span, there was enormous change. We can tell from the archaeological record we were -- we probably didn't even speak 100,000 years ago. We were just simple foragers, much like chimpanzees, maybe like Neanderthals.

But 50,000 years ago, the archaeological record tells us, there's a whole suite of very sophisticated behaviors, probably prompted by the evolution of language.

So if that amount of change can take place in that 50,000 year interval, we shouldn't be surprised that changes has also continued in the latter 50,000 year interval.

FLATOW: All right. We're going to take a break, catch our breath, talk more with Nicholas Wade, author of Before the Dawn: Recovering the Lost History of Our Ancestors, go to the phones and take your calls, talking about evolution.

We will get into, is evolution still going on? What might happen to the human race? Lots of good interesting things to talk about. Stay with us. We'll be right back.

This is TALK OF THE NATION: SCIENCE FRIDAY from NPR News.

(Soundbite of news)

You're listening to TALK OF THE NATION: SCIENCE FRIDAY. I'm Ira Flatow talking with Nicholas Wade who's a science reporter of the New York Times, author of the book, Before the Dawn: Recovering the Lost History of our Ancestors.

The number, 1-800-989-8255. We were tracing the history of divergence occurred in human populations 50,000 years ago. You talked about them being, separating into different continents and sort of inbreeding. Would that be the right way of looking at it?

Mr. WADE: Yes. That's right.

FLATOW: Talking about isolated populations, you mentioned in your book that the Ashkenazi Jews are a good example of an isolated population that has undergone many genetic changes.

Mr. WADE: Right. This was a surprise. But it's turned out from looking at the Y chromosome that the Jewish men from many different Jewish communities around the world all have the same Y chromosome.

Now, it's not specific to Jews. It's a sort of generic Middle Eastern Y chromosome. And it also is -- it is proof not only that they all come from the same source from the Middle East but also that the community has interbred, at least obviously for religious reasons.

FLATOW: Right.

Mr. WADE: So - although I don't think this all could have been predicted, I mean, because people can convert to Judaism if they wish. Nonetheless, it has turned out that, at least until recent times, Jewish communities have been endogamous, or breeding within themselves.

FLATOW: And what results in that? What comes out of that? You know, we hear about Tay-Sachs disease, for example, is a European Jewish disease.

Mr. WADE: Well, lots of…

FLATOW: What other kinds of things come out of that habit?

Mr. WADE: Well, firstly because the Jewish genetic pool has been isolated for about 3,000 years, you can tell many fascinating things about Jewish history to do with Cohens(ph), for example, the priesthood descent from (unintelligible).

FLATOW: Right.

Mr. WADE: One of the most interesting things has to do with the genetic diseases that are common to many Jewish communities. And in particular, the Ashkenazi community has a set of Jewish diseases that shows very curious clustering.

Now, diseases come about through mutations which hit randomly in the genome. So when you get the same pathway being hit, it's the sign that although the mutation (unintelligible) is a disease, there must be some benefit that far outweighs the downside of the disease.

Now, we know with the case of malaria, which is a very recent disease, about 10,000 years ago, the evolution has to use whatever mutations it has at hand. And with malaria it's used, the sickle cell mutation and the Thalassemias in different populations, to make a quick fix to the threat of malaria.

So coming back to the Ashkenazis, people have long puzzled, well, what is the upside of these mutations? To what disease does it afford protection? And there isn't one. No one can find any disease that these mutations help you with.

But a very interesting theory has recently been advanced which is while during the Middle Ages, around 900 years, Ashkenazis lived in a different social niche from their host communities because of discrimination. They were forced to go into money lending, tax farming, professions which demanded a great deal of intellectual acumen.

If you try and work out - remember, in the Middle Ages we didn't have the concept of zero. If you try and work out 17 percent of 3,000 without using zero…

FLATOW: Right.

Mr. WADE: …it's not a straightforward computation. So for these reasons, it seems very possible that the mutations that were favored in the Ashkenazi communities were ones that promoted extra intelligence.

Now, this is a…

FLATOW: It must be a controversial theory.

Mr. WADE: …you know, when I wrote about it, no one wrote in to complain. But at the same time…

FLATOW: Certainly no one Jewish wrote in to complain. But what your grandmother's been telling me as a Jewish person all these years, you know, it's backed up now by this theory.

Mr. WADE: Well, the Jewish folk lore version, as I understand it, is that it was, of course, the Rabbis (unintelligible) the merchants and the Rabbis' sons married the merchant daughters. But this is -- there aren't enough Rabbis…

FLATOW: Right.

Mr. WADE: …to make a real difference in population terms according to Henry Harpenton(ph), whose theory I'm reporting. It must have been something that happened over many generations to the population as a whole.

FLATOW: Um hmm.

Mr. WADE: But definitely, I mean, the interesting part of the hypothesis is that Ashkenazis have indeed made an enormous intellectual contribution way out of proportion to their numbers, on the one hand. And on the other hand, it's a very curious path of (unintelligible) and diseases.

So the hypothesis links the two in a very plausible way with historical backing. And what remains is for it to be put to a test. I mean, it makes it, like a good scientific hypothesis, it makes a textbook prediction, which is that people who carry any of these mutations, and I think the figure is like 70 percent of Ashkanazis carry one or other of them. And they're usually not visible. They don't cause anything bad unless you carry two copies.

People who carry these mutations should do slightly better on IQ tests than the average. No one has yet tested that thesis.

FLATOW: 1-800-989-8255. Talking now with Nicholas Wade, author of, Before the Dawn: Recovering The Lost History of Our Ancestors, on TALK OF THE NATION SCIENCE FRIDAY.

Let's go to the phones. Is that Nick in, what is it, Charles City, Iowa?

NICK (Caller): Yes.

FLATOW: Hi. Welcome to SCIENCE FRIDAY.

NICK: Thank you. My comment kind of relates to what you had alluded to before the break, and that is, what do you see happening in the next few thousand years as far as physical changes, biological changes in the human body?

Mr. WADE: Well, you can't predict for sure, but I think one can say there will be changed. I mean, if the world goes back into a new Ice Age, which will certainly happen sooner or later, we'll go through those bodily adaptations that suit you for the cold. We'll become all sort of rotund-like…

FLATOW: Hairy? Are we going to get our hair back?

Mr. WADE: Maybe we'll get our hair back if we don't need to sweat. You sure can't predict for sure, but I just think there will be changes.

It's very unlikely that we'll stay exactly as we are.

FLATOW: What about our brain? We always see, when you see science fiction or read science fiction movies, always the brain is evolving to this bigger state. Is that inevitable? Or could that go the opposite direction?

Mr. WADE: Well, you know, I think this surely has been happening. In fact we've already found several brain genes that have been under evolution in the last 50,000 years. And this surely matches the growing complexity of our societies. I mean it's much more complex to operate in one of our societies, to perform the difficult jobs that we all do than to be a hunter and gatherer; and even though hunters and gatherers know an enormous amount about their environment and the plants and the animals, they're very skilled, resourceful people, but nonetheless, there are many concepts that they never had that you get with settling down. And there is surely greater need for intellectual capacity and our brains surely has been evolving fast over the last 15,000 years, certainly since settlement, and will continue to do so.

FLATOW: Would it be able to, is it possible for us to track the changes while they're happening? Or are we inside the box and you can't see unless you're outside the box what's going on?

Mr. WADE: We, at present, it's very hard to give a date more precise than a couple of thousand years, but that's partly for lack of data. So, when we are able to sequence someone's genome for a mere thousand dollars, which we're trying to do right now, and we have a mass of data, then I think we'll be able to see evolutionary changes as they happen.

FLATOW: What would you, what kind of research, and you've been covering this for years, would you like to see? What kind of questions need to be answered or you think should be answered? I'm going to give you the blank check question I give to scientists, and you're close enough to one. I know you are. If you had all the money in the world, I give you a blank check and you can do some research, you could answer a couple of questions, what are some of the key questions that you would like answered about?

Mr. WADE: In this subject here?

FLATOW: Yeah. Yeah. Well, you could give me anything at all if you want. Where do the socks go in the laundry? That would be a good one!

(Soundbite of laughter)

Mr. WADE: Well, I mean, the standard unanswered questions are how did life begin. That is a problem that looks harder and harder the more we know about it. And the other, and the current one of course is how our brain works. So, but I'm looking at it through what the genome is telling us.

You know, one of the most fascinating things about the Ashkanazi hypothesis that I described in such detail is that this pinpoints for us exactly which of the 20,000 or the 10,000 genes active in the brain are the ones you need to increase intelligence; if the hypothesis is correct. So it would be fascinating to, by the media of genetics, to understand how our brain is wired and how we can improve it in various ways.

FLATOW: Find the intelligence gene?

Mr. WADE: And there are bound to be a whole group of them. But we could find them, we could find the other genes that determine our human nature, that determines the aspects of it we less like. And we could think perhaps about trying to improve it.

FLATOW: Well, you're saying that basically culture is influencing evolution here. Right?

Mr. WADE: That, we know from the…

FLATOW: So we're sort of influencing our own evolution by the kind of culture we create?

Mr. WADE: Exactly. And I think that's why, I think that accounts for the progress that seems so obvious when you look at the human trajectory, from living, you know, the wildest hunters and gatherers to our civilized societies today.

Evolutionary biologists do not have the word progress in their vocabulary, so how is it we've, how can you explain this progress? So I think the answer must be what you just put your finger on. We know from that lactose tolerance gene where people who kept cattle developed the genetic ability to digest milk in adulthood. We know that culture feeds back on the human genome. So that is a way for human choice to feed back on the human genome.

So if you live in a society that favors trading conciliation over aggressiveness, and allows the trait as the conciliators to have more children than the warriors, then that would be a way for human nature to change in a way that supports more complex, more peaceful societies. And I believe that's exactly what has happened in history.

Our societies are far more peaceful, complex, and cooperative than any time in the past.

FLATOW: But you have to foster that then, for that to happen. If you want smarter people, you have to create a smarter culture. If you want peace, more peaceable people, a peaceful culture. Because then that will influence the evolutionary process. Is that what you're saying? Or am I putting words in your mouth?

Mr. WADE: That's right, except we don't have to do it. It's been done for us. Because war-like societies, of which there have been many in history, have not won out over more peaceful societies. The more peaceful societies have prevailed and with them the more peaceful genomes. And that's why the arrow of progress has pointed upward, though not always so. Mostly upward, it's gone.

FLATOW: But you have to be dominant then, whatever that culture is influencing?

Mr. WADE: Well, that's nature's way. We are fortunate if peaceful, if societies that are on the whole peaceful have prevailed over ones that have been more war-like.

FLATOW: Um hmm. We're talking about evolution and all kinds of stuff with culture this hour on TALK OF THE NATION SCIENCE FRIDAY from NPR News.

I'm Ira Flatow with Nicholas Wade, author of Before the Dawn: Recovering The Lost History of Our Ancestors.

Let's talk about, in the few minutes we have left, the subtitle of your book, recovering the lost history of our ancestors. That is by looking through the genome?

Mr. WADE: Right.

FLATOW: And why is it a lost history? Because the fossil record is incomplete? Or we just, the genome is a better place to look for it?

Mr. WADE: Well it, I think it's lost because there are so many, sort of blank pages in our history. You know, from about 50,000 years ago to 15,000, which is when you see the first settlements, there are almost no records left of what we did except for a few stone tools and the painted caves of Europe. It's all gone. So you might think it would be impossible ever to reconstruct what happened then, and yet the genome gives us a way of doing so. At least sketching out the broad outline of what was happening.

FLATOW: But it couldn't tell us, you know, so-and-so lived in a certain place? Is it that precise that it could do that?

Mr. WADE: You know it's going to be able to. There's going to be a grand synthesis which we can already see happening between genetics and archeology. Because the geneticists can say, well, the (unintelligible) nations, the people you archeologists call (unintelligible) nations from the stone tools you've found, we know these belong to lineage 453 of the genetic tree of the Y chromosome. So you can begin to link up genes with archeological sites and cultures.

And the third ingredient of that, of course, is language. If you can work back, the tree of languages from those we speak today to the original mother tongue of the ancestry of the human population, you should be able to make language the third part of this synthesis between genetics and archeology.

FLATOW: I remember asking Louie Leakey this question over 35 years ago when I first met him as a young scientist, as a young reporter, and I asked him what, you know, I was just sitting in this room in aw of Louie Leakey, I was in my 20s, and I had to come up with a question. And I asked him, what separates us from, you know, proto-humans and chimpanzees and whatever, and he's talking about the precision grip and tool-making abilities. That doesn't seem to be so true anymore, with the discovery of tool-making abilities of chimps and them teaching one another how to, you know, to make tools. Maybe not as precisely as making a watch.

Mr. WARD: I think that's right, because Leakey at that time must just have discovered homo habilus and the first toolmaker.

FLATOW: Yes. Right.

MR. WARD: But the more we know of chimps, the more we realize how many of their abilities parallel our own, and in particular tool-making, although the binobos(ph) don't have that.

FLATOW: Right. I always ask chimp people, you haven't studied binobo? We had a guest on and I asked, what's the difference between a binobo and a chimp? He said if I give an empty box to a chimp, two chimps with fight over it. If I give it to a binobo, they'll go inside and make love.

(Soundbite of laughter)

FLATOW: We're always confounded by the tiny bit of genetic difference between us and the chimps that account for so much.

Mr. WARD: Well, I think that's right. You now, it's clear there must, it seems to me there must be a sort of set of genes that influence our social behavior. A sort of social template. And we and the chimps and binobos must all have inherited it from our common ancestor.

But you just tweak it a little bit and you get societies as totally different as the chimp and the binobo. And you tweak it a bit more and you get our society, rather the variety of human societies.

FLATOW: It's almost like the chaos theory. You just need, you know, a tiny little tweak and some big cascade.

Mr. WARD: Except that it all makes sense because the tweaks are imposed by the environment. So if you live in an environment, say, in a settled society where you have resources that you, and surpluses that you've been able to store and hoard for the first time, then the people who sort of figure out how best to manage their surpluses will be the ones who have more children. And that way the society will sort of come to conform to that environment.

FLATOW: Well, we've run out of time. It goes by fast, doesn't it?

Mr. WADE: It sure does.

FLATOW: Nicholas Wade, thank you for joining us today. He's the author of Before the Dawn: Recovering The Lost History of Our Ancestors. He's one of the great science writers of our time and he always writes terrific stuff.

Thank you for taking time to be with us.

Mr. WARD: Thank you, Ira. Thank you very much.

FLATOW: You're welcome.

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