by Lev ZHIVOTOVSKY, Dr. Sc. (Biol.), N. I. Vavilov Institute of General Genetics, Russian Academy of Sciences
In December 2003 a venerable medical journal, The Lancet of Great Britain, named the world's best publication in the field of medical and biological sciences. It was an article co-authored by an international team of scientists (comprising N. A. Rosenberg, J. K. Pritchard, J. L. Weber, H. M. Cann, K. K. Kidd, L. A. Zhivotovsky, and M. W. Feldman) and published in the US journal Science. This article dealt with the genetic structure of human populations.
One of the outcomes of this study boiled down to this: is it possible to identify an individual's ethnicity from DNA characters? We studied DNA variation among 1,056 individuals representing 52 ethnic groups throughout the world-in North, Equatorial and South Africa; in West, Central and East Asia; in Europe and Oceania; and in Central and South America. Russia was likewise represented-by the Russians, Yakuts and Adygei. In the study we used a total of 377 DNA characters (loci) not associated with adaptive properties or any visual traits. We just "marked" genomic loci in every test subject (and that is why the corresponding loci are often called "DNA-markers").
We assigned a definite number К (mainly from 2 to 5) and then subdivided the entire sample into particular "DNA-groups" in keeping with genetic relatedness; however, we did not use data on the ethnicity of this or that person. And then we analyzed
A sample of 1056 individuals from 52 populations subdivided into related groups according to 377 DNA characters. The number of different groups of individuals (K) is color-coded in each diagram. All 52 populations are separated from one another by a vertical strip. Each individual is represented by one or several hues depending on the proportion of DNA loci (characters) for a corresponding group. For instance, at K=5 both populations from Oceania (green), albeit quite distinct from other groups, include individuals with loci characteristic of the peoples of East Asia (pink) and Eurasia (blue), while one of the populations of sub-Saharan Africa (Pygmies of the Biaka tribe) has an individual (blue column) akin to the West Eurasia group. (by Rosenberg et al. 2002).
how many representatives of a particular ethnic group turned up in each group.
Our results proved stunning: nearly 100 percent of the DNA samples occurred to be race-related. Thus, at K=2, all the representatives of the Negroids (African, or Black) and Caucasoids (Eurasian, or White) races came to be in the same DNA-group; while landing in the other group were people of the Mongoloids (East Asia and American Indians) and Oceanic races. At K=3 the first group was subdivided into African and Eurasian races, while the other one remained unchanged. At K=4 the division into Negroids and Caucasoids kept up, but the American Indians separated from the Mongoloids. At K=5 no changes were registered in the Negroid and Caucasoid races, while the Oceanic race showed clear separation from the Mongoloids.
Thus, taken aside from external characters like color of the skin a total of 377 DNA-markers (in this sense, random characters) made it possible to determine the racial identity of each of more than a thousand individuals chosen arbitrarily. We should just as well note that some individuals revealed a significant percentage of interracial characters.
Well and good, but what about the situation within races? Can we identify smaller ethnic groups in there? Yes, by and large. For instance, the Eurasians clearly branch into the peoples of Europe, the Middle East, and Central/South Asia; however, should we take a particular region (Europe, as an example): here any ethnic group includes individuals who, by their DNA characters, could be assigned to a different group. Thus, living in Equatorial and South Africa are the oldest hunter-gatherers on earth: the Pygmies (Biaka and Mbuti) and the San tribe; these three groups exhibit certain distinctions. At the same time, three other, not so ancient peoples of Africa, appear akin enough to fall in one, common cluster. The American Indians clearly break into five tribes: the Pima and Maya of Central America, the Colombians of South America's north, the Surui and Karitiana from the Amazon river basin. Two populations from Oceania are dissimilar, too.
But do these distinctions mean that races are secluded groups which a zoologist could well assign to several species or subspecies according to a zoological taxonomy? No, they are not. To see that, one should quantify differences among individuals according to their DNA characters within races and compare these differences with those between peoples regardless of their ethnicity.
True, they can differ more or less according to 377 DNA markers. Say, two arbitrarily chosen individuals may differ in 10 characters but be identical in the other 367, while
Diagrams on pp. 34 - 36 are published with the permission of Science magasine (N. Rosenberg at al., SCIENCE, 298:2381 - 85, 2002).
A sample from Europe, Middle East, Central and South Asia subdivided into groups according to 377 DNA loci (characters), (by Rosenberg et al. 2002).
another pair may be different in 20 but identical in 357. We assumed the mean differences between individuals in the total sample to be 100 percent. But when we estimated genetic differences within each race, they proved to be above 90 percent, which means that purely interracial distinctions accounted for less than 10 percent of the entire genetic diversity. Thereby we can conclude that the races are just large human populations, and no taxonomic criterion could enable us to assign them even to subspecies. Such a small genetic differentiation is quite usual for populations of one species both in animals and plants.
So, racial differences revealed by DNA-markers not at all mean significant genetic differences-as a matter of fact, there are more points of similarity than differences. Naturally, this question arises: to what extent humans genetically differ from one another? And how much are individuals alike?
GENETICALLY WE ARE BOTH LIKE AND UNLIKE
According to scientific findings, genetic differences between humans cover only a thousandth part, or 0.1 percent, of the human genome. Now, is it large or small? Here are some thumbnail calculations. The human genome contains about 3 bin nucleotide pairs, which means that all the people of our planet differ in three million positions. Say, if one person has the nucleotide T at a certain position, others may have А, С or G at that position. Accordingly, the number of hypothetically possible types of DNA should be at least 23,000,000 , or a great deal more than the human population of the globe, ca. 233 .
Yes, we all are much unlike-genetically. But only with respect to a thousandth part of the genome; and we are much alike in 99.9 percent of the genome! Actually, the homology is even higher than that, for most of the distinctions occur in the "silent" parts of DNA and do not affect its functionally significant fragments. Let us stress this point: the basic, essential genes are identical in all people. For example, let us consider a hemoglobin molecule which plays the key role in the transfer of
A sample from Africa, East Asia, Oceania and America subdivided into groups according to 377 DNA loci, (by Rosenberg et al. 2002).
oxygen from the lungs to all cells of the body. Its composition is identical for all normal individuals. Substitution of just one amino acid for another alters the highly complex configuration of the hemoglobin molecule and reduces dramatically its oxygen transportation capacity, thus causing a disease. The same holds for many other functionally important genes as well.
Every individual inherits part of the biological, genetic relatedness back from the dim and distant past-over dozens and even hundreds of millions of years. Now let us compare man with a crocodile. Needless to say, both are far apart in the composition of DNA, and also sit far apart on different branches of the phylogenetic tree (the latter highlights the biological relatedness of organisms). But if we compare man with a dog, which is much closer to us evolutionarily, we turn out to be more related to this animal in DNA as well. And should we compare Homo sapiens with the apes (such as the chimpanzee), the level of DNA homology will be quite impressive: on the average we differ only in one or two nucleotides per hundred. This means that our genetic homology is as high as 98 - 99 percent! But a genetic difference of 1 to 2 percent is quite enough to make the level of relatedness very remote-unlike outwardly, we are incompatible in reproductive terms, too. And so, man and chimpanzee are two different zoological species separated by at least 5 mln years and having traveled a long pathway of evolutionary transformations.
Now how can we marry these two views: that all humans, though genetically akin to one another, are much different in the same breath? Let us compare what may seem two so different groups of people, the native Americans (Indians) and the Europeans. Yes, they look different in their appearance but only because, living in human society, we are apt to spot very slight distinctions. The ability to distinguish those is a matter of experience. Recall Mowgli who could readily differentiate among the wolves and other beasts of the jungle because he lived among them.
The high genetic relatedness amongst people is a sequel to a short evolutionary pathway which the human race has traversed for some hundreds of thousands of years. Say, the Neanderthal man seems to have little in common with our contemporaries. But if we "dress him up"-in a suit, hat and all-he will look a gentleman like you and me. The author of the present article was giving a lecture on the theory of evolution and showed this cartoon to the students. One, happy about his guess, exclaimed: "Oh, that's you!"
Human individuals may differ in hundreds of thousand and even millions of nucleotides and in some characters as well (like color of skin, facial features, head shape, etc.) to which we are prone to attach so much importance; but all these distinctions are negligible if compared with a nearly one-hundred percent (99.9 percent) genetic homology. Thus all inhabitants of our planet are genetically related, they are genetic cousins of sorts.
And now let's see whether the results of our DNA study concur with what anthropologists are saying about ethnic groups.
People, inhabiting different geographic regions and countries, come to form various ethnic groups differing in looks, life styles, languages, mores, customs and faiths. More often than not, the language, customs and religion are the same among people in a particular region. And yet they can undergo dramatic changes even within the life span of one generation. Migrating to other countries, adults have to learn a foreign language which becomes a native tongue for their children and grandchildren; certain individuals and even peoples can change their faith-just recall the baptism of pagan Rus in the year 988. The culture (language, faith, customs, social behavior, mode of existence) is a social milieu, and a baby born into it adopts the customs and traditions from its parents and other people.
People, however, are different not only in terms of culture, they are different genetically, too. Genetic characters are passed from parents to children regardless of what they have learned or seen. Unlike culture-conditioned characters, genetic traits change very slowly, in hundreds of generations. The natives of different continents are most unlike in their visible hereditary features like color of the skin, hair and eyes; they differ in the form of their body, skull or nose; and in whether their hair is lank, wavy, kinky or curly. And so forth. The geographically isolated "continental" groups are called races, and their distinct features-racial, respectively. Most of these features may vary, and their complete set proper to any particular race is but seldom present in a concrete individual. Besides, human races are not absolutely isolated from one another. Ever since the emergence of Homo sapiens different tribes have been intermixing all along. And each of the large races is not homogeneous but consists of smaller components with characteristics of their own. For instance, the American Indians assigned to Mongoloids have no epicanthus (a small fold of skin sometimes covering the inner corner of the eye), and their facial profile is quite European. The Oceanians, though dark-skinned, differ from the Black Africans in the length of their hair, and in the set of their teeth; and in their dermatoglyphics (skin patterns) they come closer to the Mongoloids. The Caucasoids, too, comprises several anthropological types. And there are so many ethnic minorities!
Thus, the division of humankind into large and small races suggested by anthropological characters (pigmentation of skin and hair, skull form, etc.) well agrees with the "sorting" by means of "neutral" DNA-markers (i.e. unrelated to morphological or physiological characteristics) into specific ethnic groups-something that we have described above.
HOW RACES CAME INTO BEING
Studying the diversity of DNA in contemporary peoples, one can estimate the size of an African ancestral population from which, if we are to believe the common hypothesis, we originated. Using the same DNA data we have shown that it wasn't large, just about two thousand. But this is not to mean that other human populations were not in existence then. And yet the genetic diversity of all the humans comes from that small tribe, for the others have left no genetic traces in the present-day peoples. Comparing the DNA-markers of sub-Saharan Africa's aborigines, we have found that about 70 - 150 thousand years ago that tribe experienced intensive demographic differentiation that resulted in the appearance of most diverged populations within the African continent. And it came to pass that 50 to 100 thousand years ago waves of migrants started spilling out of Africa. The processes of migration and adaptation to local conditions took dozens of thousands of years. Suppose that a group of people came, say, to Southeast Asia and settled there for many generations. Some moved further to give rise to a new local population (a future tribe, ethnic group, nation). This local population has common history and common ances-
tors with the parental group; consequently, these people have a higher DNA homology among themselves than with the inhabitants of other continents. As to the populations of large land areas (the large races of the future), their DNA in subsequent generations diverged due to mutations and geographic isolation due to huge geographic distances between them. All that was concomitant to ancestor/descendant divergences, and that's what the neutral DNA-markers tell us. As to adaptive differences, these must have been developing alongside the growing distinctions in DNA and evolving as a result of adaptation to climatic and geographic conditions, to the type of food and the landscape of a particular region. All that told on the development of culture and language independently from the inhabitants of other regions. Also, processes other than the divergence of populations impacted the formation of cultures and languages. New ethnic communities could appear through the intermixing of groups of different ethnicity. Mass migrations, interracial marriages and mongrelization are capable of decreasing the genetic distinctions evolved, and they can make it fast, within a few generations. That is, races and intraracial ethnic groups are not a standstill category dividing people in keeping with the essential, basic biological characteristics. Not at all. Race and ethnic community is a historical, evolutionary notion.
There are two points of view concerning interethnic differences. First: human individuals and peoples at large are genetically much unlike and, therefore, not equal. Second: the observable distinctions amongst people are conditioned not by the genetics, but are rather due to external factors, social factors, too.
Modern scientists turn down these two viewpoints as far gone. The interracial and interethnic differences are not as great to cause any biological inequality: conditioned evolutionally, these differences are capable of changing. On the scale of human history, all of us emerged from one and the same "nest", so to speak, relatively not so long ago.
More than that, living conditions can largely impact the growth of the organism, while different environmental conditions in which various ethnic groups live can cause considerable physical distinctions. For instance, the aborigines of hot deserts are tall and have thin calves of their legs. Their body build is adjusted to life on parched, arid ground. By contrast, the Pygmies of Africa are short. Under the canopy of the woods they live in, heat combines with high humidity, and the ratio of the body surface to its volume holds advantage in terms of convective heat exchange if a person is short and stubby.
Inherited diseases within ethnic groups are likewise related to evolutionary processes. Such diseases occur in the form of detrimental mutations that impair the functionally significant genes inherited by the progeny, should the parents reach the reproductive age. A definite mutation, if it persists, first spreads among the closely related populations and then affects more distantly related groups via migration. Further expansion of detrimental mutations can be caused by random processes and local selection to give rise to inherited pathologies in this or that region. These trends lead to changes in a spectrum of inherited diseases afflicting not only different races, but also populations within a race. Yet the propagation of this or that disease may be inhibited or stimulated depending on specific environmental factors.
There are of course definite genetic differences among ethnic groups; therefore, using DNA-markers for practical purposes, e.g. in searching for candidate genes for diseases, personal identification, etc., such differences should be considered as well. But when we come to the level of intelligence, we should not accentuate them overmuch. Such things as deviant behavior and crime can hardly be conditioned genetically. Let us take the well-known intelligence tests through IQ, the intelligence quotient.
Numerous studies claimed that the Africans had a lower IQ than the Caucasoids. And yet the Japanese performed better than the latter. As a matter of fact, this quotient as an indicator of one's intellectual level has proved to be not objective at all, for it was invented by technocrats who would measure another man's foot by their own last: they who grew up in a definite social environment applied their own yardstick to quite different societies. Now imagine an IQ test suggested by black hunter-gatherers: many whites would have appeared simpleminded!
And here we come to another important subject - the impact of a social environment, family and culture. A small child looks at its parents and imitates them. Should it be born into a musician's family, it will have the good ear for music from the tender nail. This child win not be bored by long music lessons. It is most unlikely for such diligence to be recorded in its genes. True, prodigies may have a unique set of genes, but such talents can be realized only in a definite milieu, while this very set of genes may "come apart" in the next generation.
It has become fashionable now to point at genetic fatality when dealing with behavioral aberrations. No direct evidence is available on that, barring cases of genetic defects responsible for mental disorders. But in this case medical and social treatment, as well as measures for crime prevention, necessitate. One cannot wait and see here. However, in the absence of pathologies, inherited or acquired, there are many facts to confirm the leading role of perception, imitation and motivations in fostering one's skills and talents. Genetics cannot justify criminal behavior, homosexual aggressiveness, sloth, aversion to work, and so on. Any sound individual is the master of his fate.
Permanent link to this publication:
LVietnam LWorld Y G