Download INTERVIEW WITH RICHARD LEWONTIN edited transcript Richard

INTERVIEW WITH RICHARD LEWONTIN
edited transcript
Richard Lewontin, Alexander Agassiz Professor Emeritus of Zoology at Harvard University,
is one of the world’s most eminent authorities on human diversity. He has written many
celebrated books on evolution and human variation books including Human Diversity, Not in
Our Genes and most recently, The Triple Helix.
Does racial difference exist on a genetic level?
Peoples who have occupied major geographical areas for much of the recent evolution of
humans look different from one another. Sub-Saharan Africans have dark skin and people
who live in East Asia tend to have a light tan skin and an eye color and eye shape and hair
that is different than Europeans. So there is this kind of genetic - it is genetic - differentiation of some features of the body between people who live in Central Asia, Africa, Europe,
North America, and South America.
And those features, which are geographically determined, were used to erect notions of
different races. There’s the African race, the Black race, the Yellow race, the Red race, the
Brown race, and the White race. And it’s mostly skin color plus hair shape and eye shape
and so on. That’s the everyday observation, that “they” all look alike - and we all look different.
The real question is not whether those differences in skin color and hair form are genetic,
because they are. We know that because the children of black slaves brought to North
America were the same color as their parents were. The question is what else does that tell
us about biological differences? How much difference in other genes beside the genes that
are relevant to skin color is there between these major geographical groups?
If we want to use the notion of race in a sensible, biological way, we could only do that if
there really were a lot of genetic difference between those groups aside from the superficial
differences that we can see. And that’s an important issue which we now understand. We
understand it because over the years a lot of data were gathered by anthropologists and
geneticists looking at blood group genes and protein genes and other kinds of genes from
all over the world. Anthropologists just went around taking blood out of everybody.
I must say, if I were a South American Indian, I wouldn’t have let them take my blood,
but they did. And one of the consequences of that is by the early 1970s, we had a huge
amount of information about the different genetic forms all over the world for a large number of genes that had no relevance to those outward manifestations like skin color, but had
to do with blood type and proteins.
And when you brought all that together, it became pretty clear that there really were minor
differences in the frequencies of the different gene forms between the major geographical
so-called races.
Since the 20th century, it’s been recognized that there’s what’s called polymorphism of
blood type. There are type As and type Bs and type Os and Rh-positive and Rh-negative
and so on in every group in the world. But the assumption was that people in Africa would
have a very different relative frequency of A and B and O than people would in North Amer-
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ica or in Europe and in Asia.
And what all these studies showed was that that wasn’t true. That you couldn’t really tell
the difference between an African population and a European population and an Asian
population by looking at the frequency, the relative proportions of the different blood types.
They were essentially the same in all these groups.
That isn’t true for every blood type. There are occasional types which are strongly differentiated between populations. There’s one blood type called the Duffy blood type and that’s
very different between Asians, Africans, and Europeans. But that’s an exception rather than
a rule.
For almost every gene we know, either everybody in the world has the same form of the
gene, in which case all human beings are the same, or if there’s variation, the frequencies
of the different variants are the same relatively speaking, close to the same, in Africans,
Asians, North Americans, Austro-Asians, and so on. And only about - well, I estimated 7%
of all of human genetic variation could be ascribed to differences between groups, between
major races. Anyway, about 75% of all the genes [come in only one form and] are identical
in everybody. So there’s very little differentiation.
How do you measure human genetic variation?
The way we measure human variation genetically is to look and find all the different forms
of a particular gene, the alternative forms of a gene, and then see what percentage of the
population has form one, form two, form three, form four, form five, and so on. Now if 99%
of the population has one form and only 1% has another then there isn’t much genetic variation in the population for that. And if different populations all have 99% of form one and
1% of form two, then there’s no differentiation between populations because they have all
the same percentages.
If on the other hand one population had 99% of form one and 1% of form two but some
other population had 99% of form two and only 1% of form one, then even though within
the population almost everybody is the same, between the populations there’d be a big difference.
So that’s the way you characterize it. You see the percentages of the different forms in different populations and you ask -- If I take a sample from one population, are proportions
of the different forms similar whether it’s an African population or an Asian population or a
European population? If so, there’s no difference BETWEEN populations, and all the difference is found WITHIN populations.
So what did you discover about population differences?
Well, the problem back then for evolutionists and population geneticists was always to try
to actually characterize how much genetic variation there was between individuals and
groups and so on. And nobody knew how to do that because you had to connect genes with
some outward manifestation that you could actually observe, and most genes don’t have an
outward manifestation in their variation.
So people didn’t really know whether individuals varied genetically a lot from one another
or only a little bit. They could see variation between individuals but they didn’t know how
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much of all the genes that variation represented. And for a very long time, nobody had the
faintest idea how genetically variable our species was from individual to individual.
And I spent a lot of time worrying about that like other people in my profession. And then
I met a guy who had an experimental gimmick and he didn’t know what to do with it, but I
knew what to do with it. So I was sort of a person with a problem without a method and he
was a guy with a method without a problem and we got together.
And that method was essentially to extract proteins from individuals and to run them in an
electric field and to see whether the proteins moved at different rates in an electric field.
If there were alternative forms of the genes that were for that protein, then the proteins
would move at a different rate in the electric field, and you could visually identify the proteins by staining them.
So what you did is you ground up a fruit fly, you stuck it in a slab of jello, you turned on the
current, all the proteins moved in the jello, and you turned off the current. You stained it,
and sure enough you would see that different individuals had the same protein moving different distances. And that would be because they had a different form of the same gene.
And that method, which is called gel electrophoresis, a very fancy name, we were able to
use it on any organism at all. If you could grind it up, you could do it, and that included
people. You didn’t have to grind up the whole person, but you could take a little bit of tissue or blood; you could do it on flies, on mice, on plants, on bacteria, anything. And the
result was for 20 years people interested in this question of genetic variation were grinding
up organisms and measuring the genetic variation.
And what they discovered was that organisms within a species were tremendously genetically different one from another. Many people had said, “No, they’re all the same because
any genetic differences are mutations and they will be selected out by natural selection.
And except for a few superficial differences, everybody in a species is the same.”
But that’s not true. It turns out that between 25-33% of genes within a species are of the
variable kind. They differ from one individual to another. And that’s what that method discovered, that something around a quarter or a third of all your genes -- not your genes, but
genes of any organism -- are variable between individuals of the species. So that gave us
a different view of the possibility of evolution. And I thought, “Well, this raises the possibility that we could ask how much genetic differentiation there is between humans in different
population groups.”
It had already been established by a guy named Harry Harris that there was a lot of this
genetic variation in humans, the kind that we have found in fruit flies, that people have
found in plants. He used the same technique and showed that humans are genetically variable. But what he didn’t know was how much difference there was between Africans and
Asians and Europeans and so on. But a certain amount of that data began to accumulate,
and by 1972 a lot of those data existed.
We could then tell from older data on human blood groups, which were known for a long
time, and from this more recent data on their proteins which we could visualize in these
gels, how much difference there was between any two individuals genetically and between
a collection of individuals from France and a collection of individuals from French Equatorial
Africa, and from Asia. And that collection of data is now huge, I mean, we know an im-
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mense amount about that kind of protein variation in humans. That was before people were
sequencing DNA. That’s when we were just looking at people’s proteins.
And so I thought, “Well, we’ve got enough of this data, let’s see what it tells us about the
differences between human groups.” And so I just looked into the literature, and that literature was in books and so on. And so one day I was going to give a lecture, I think it was in
Carbondale, Illinois, or somewhere south. I was working in Chicago at the time. So I took a
couple of these books with me and a pad of paper, and a table of logarithms which I needed for this purpose, and a little hand calculator, and I sat on this bus trip for three or four
hours looking at the books, picking out the data, looking it up in the table of logarithms,
doing a calculation, and writing it down in tables.
And when I got back after the round trip I had all the data I needed to write the paper
about how much human genetic variation there was, and so I did it. And that’s been repeated in recent years using DNA and so on. You always get the same result. Shows you
it’s worthwhile being afraid to fly, by the way, because you have lots of time on a bus to
work.
So how much difference is there between human groups?
And the numbers come out as follows:
Roughly speaking for human beings, for about three-quarters of all our genes, everybody
in the world, except a rare individual, has only one form of the gene. So all human beings
share that form. For the 25%-33% or so of those genes for which there is some variation
- 99 to one or 50/50 or 75/25 of different forms - for almost all of those genes, it doesn’t
matter from which population you take the sample; they have the same proportions. That
is to say, if it’s 75% of Form One and 25% of Form Two in Europeans, it’s 70% of Form One
and 30% of Form Two in Africans and 73% of Form One and 27% of Form Two in Asians,
and so on. Most genes are like that.
But there are a very few genes, like the Duffy blood group, in which in Asian populations
there is one very common form, in African populations there are two forms, but they’re not
the same as the common one in Asians, and in Europeans there’s another different ratio. So
for that gene, there’s a big difference in the frequencies, but that’s rare.
And if you put it all together - and we’ve now done that for proteins, for blood groups, and
now with DNA sequencing, we have it for DNA sequence differences - it always comes out
the same: 85% of all the variation among human beings is between any two individuals
WITHIN any local population, 85% of all the variation; please remember that 75% of all
genes are identical for everybody. But of the variation there is, 85% of that is between individuals within Sweden or within Denmark or within the Ewee or the Ki-kuyu or the Chinese
or something.
Of the remaining 15% of human variation, it’s roughly a 50/50 split of the variation between nationalities within what used to be called a major race, between Swedes, Italians,
French, and so on, or between Ewee and Ki-kuyu and Zulu or something. And the other
remaining 7% or so is between those major groups -- the blacks, browns, yellows, red, and
whites.
What does that tell us about race?
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Well, it might have turned out that there were big genetic differences between groups, and
that most genes were highly differentiated between the major races. Now, if that turned
out to be true, then at least it would be a possibility, although not demonstrated, that there
might be, as some like to dream, high differentiations between groups in their mental abilities or in their temperaments or anything like that. Although nobody knew about any genes
for those things, at least it was a living possibility.
But when we found that there were practically no genetic differences between groups except skin color and body form and a few things like that, it became a great deal less likely
and less interesting to talk about genetic differences between groups. And the consequence
is that from the biological standpoint those major so-called races - black, brown, yellow,
white, and red - were not biologically interesting.
And that in turn meant that the differences that people were constantly emphasizing for
social purposes were social constructs which almost certainly didn’t have any biological
basis. And therefore we should stop talking about major races because to talk about major
races gave the impression that there were big differences between these groups in things
that mattered - I mean, skin color, after all, doesn’t matter except in some vague aesthetic sense - but things that really mattered: people’s characters, their intelligence, their
behavior, whether they’re going to compete with other people or not and so on. The evidence then became that there weren’t any interesting differences in such things, and so we
should stop talking about race.
http://www.pbs.org/race/000_About/002_04-background-01-04.htm
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