Contents | April 2001
In This Issue (Contributors)
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The Genetic Archaeology of Race - Page 3
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How Different Are We?
AFI's efforts to derail the Human Genome Diversity Project can be seen as a noble attempt to protect the powerless. They can also be seen as tragically misguided. If activists succeed in fomenting widespread distrust of genetics research, they could ruin an opportunity to discredit the essential notion underlying racism—that human groups have innate and fundamental biological differences.
This idea has deep roots. In 1758 the Swedish botanist Carolus Linnaeus gave the human species its formal name, Homo sapiens. He also divided the species into subcategories: red Americans, yellow Asians, black Africans, and white Europeans. He described Homo sapiens americanus as "ill-tempered, ... obstinate, contented, free." Homo sapiens asiaticus was "severe, haughty, desirous." Homo sapiens afer was "crafty, slow, foolish." And Homo sapiens europaeus was—of course—"active, very smart, inventive."
Similar prejudices characterized biological thinking well into the twentieth century. From 1910 to 1930 most of the leading human geneticists in the United States actively supported the campaigns of eugenicists to limit reproduction by those deemed biologically inferior, including Eastern Europeans, Jews, and people with mental disabilities. This line of thinking led directly to the gas chambers of Nazi Germany, which effectively ended the eugenics movement. Yet the basic tenet of eugenic thinking—that the mental attributes of human groups differ for genetic reasons—remains firmly embedded in the popular imagination.
Until very recently most geneticists professed agnosticism on this issue. They said that not enough was known to assess the contributions of genetics to behavioral differences among groups. The data collected by Cavalli-Sforza and other population geneticists have been making that position less and less tenable. People are too closely related—and have mixed too much throughout history—to differ in fundamental ways.
Interpretations of this research have been controversial in the past, but the genetic evidence is now overwhelming. It clearly indicates that sometime in the period 100,000 to 200,000 years ago our ancestors went through a severe genetic bottleneck. Perhaps an environmental change drove ancient people to the brink of extinction. A more likely scenario, however, is that a relatively small group, numbering fewer than 20,000 at times and probably living in eastern Africa, was isolated for many thousands of years from the many groups of archaic human beings scattered throughout Africa, Europe, and Asia. The people who emerged from this genetic bottleneck had traits never before seen in human beings. They had lighter builds, new ways of interacting among themselves, and perhaps a greater facility with language. Eventually the descendants of these people spread throughout Africa and beyond. They reached Australia at least 60,000 years ago, probably traveling from the Horn of Africa and then along the South Asia shoreline. They arrived in the Middle East a bit more than 40,000 years ago. By 35,000 years ago anatomically modern people had spread into Europe from the Middle East and into East Asia from Southeast Asia. Sometime more than 12,000 years ago they entered the Americas.
Elsewhere on the Web
Links to related material on other Web sites.
Evolution of Modern Humans: The Biological and Cultural Evolution of Archaic and Modern Homo sapiens
A site offering descriptions, charts, and timetables documenting the evolution of modern humans. Created by a professor at Palomar College, San Marcos, California.
Whenever modern human beings came in contact with their archaic counterparts, the latter eventually disappeared. Many questions surround this process. The genetic evidence indicates that modern people bred very little with the archaic people living throughout the Old World. According to Joanna Mountain, a Stanford anthropologist who has been studying the genetics of African groups since the 1980s, when the Peace Corps took her to Kenya, "If the ancestral modern human population fifty thousand years ago had been highly diverse genetically, as it would have been if there had been a lot of mating with archaic peoples, we would still see evidence of that diversity today, but we don't." One possibility is that modern and archaic human beings did mate, but were so different genetically that such matings were infertile. Or maybe some matings between archaic and modern human beings did produce offspring, but at such a low rate that the archaic genes have been diluted out of existence.
How modern human beings replaced their predecessors also remains a mystery. Archaeological evidence indicates that bands of modern and archaic people sometimes lived near each other for thousands of years. Yet no remnants of warfare have been found. The cave paintings of Europe, some of which date from the period when modern people were replacing Neanderthals, evince plenty of violence against animals but not against other people.
Fewer than 10,000 generations separate everyone alive today from the small group of Africans who are our common ancestors. That's much more than the twenty or so generations mentioned in Genesis, but it's the blink of an eye in evolutionary terms. Even over thousands of generations human groups have not differentiated in any substantial way. Rather, the genetic evidence indicates that modern human beings have expanded as a single, relatively well mixed population without subsequent genetic bottlenecks (bottlenecks tend to erase the evidence of previous bottlenecks, which is how geneticists know that the bottleneck in Africa was the most recent one). Our comparative youth as a species accounts for our extreme genetic homogeneity. The chimpanzees living on a single hillside in Africa have twice as much variety in their DNA as do the six billion people scattered across the globe.
There's another reason for our biological homogeneity. Modern human beings have never been able to resist for long what Noël Coward called "the urge to merge." A person traveling due east from Madrid to Beijing (both at about 40°N latitude) would pass Italians, Greeks, Turks, Armenians, Uzbeks, Tajiks, Kyrgyz, Uighurs, Mongolians, and Han Chinese, among others. All these groups resemble their immediate neighbors more than they do groups farther away because of the continual exchange of mates across group boundaries.
There's a simple way of describing our genetic relatedness. Not only do all people have the same set of genes, but all groups of people also share the major variants of those genes. Geneticists have never found a genetic marker that is of one type in all the members of one large group and of a different type in all the members of another large group. That's why ethnically targeted biological weapons would never work. Every group overlaps genetically with every other.
The extreme interpretation of this observation, now popular in academia, is that biological groups do not exist. That's obviously absurd. The ways in which typical Nigerians, Koreans, and Norwegians differ physically belie any claim that all human groups are somehow "socially constructed." But the development of morphological differences in a widely distributed species is a biological commonplace. Whenever the members of a group are more likely to mate inside the group than outside, the frequency of particular genetic markers within that group can become higher or lower. In most cases these changes are entirely random, as with the blood-type distributions that Cavalli-Sforza studied in Italian villages. But natural selection can also be a factor. To take the classic example, as modern human beings moved from equatorial regions into more-northern latitudes, dark skin was no longer needed to protect the body from the sun's ultraviolet rays, and light skin made it possible for the body to produce more vitamin D. The resultant lightening of skin color seems to have occurred at least three times during human history: when Africans moved north into the Middle East and then into Europe; when dark-skinned people living on the islands and mainland of Southeast Asia migrated into what is today China; and when people from southern India moved north into the Punjab (genetics research is demonstrating that migrations of European people into the Subcontinent have had much less biological significance than is commonly assumed).
"What we see is the surface of the body, but the surface of the body is determined by climate," Cavalli-Sforza says. "Adaptations to climate have to be superficial, because those are the parts of the body that are exposed to the outside world." New Guinea highlanders and sub-Saharan Africans are about as different from each other genetically as any human beings on earth. Yet they have physical similarities because of where they live, including dark skin to protect against the rays of the sun.
Biologists have several options in describing the variation they observe in people. They can label an individual purely in geographic terms, based, for instance, on the distance he or she lives from the Equator. Or they can sort people entirely in terms of the genetic differences they find. Instead they tend to use the labels generated by our highly fractious culture, even though many of these labels have little to do with the underlying genetics. In this way biologists endow those differences with much more weight than they deserve.
Copyright © 2001 by The Atlantic Monthly Group. All rights reserved.
The Atlantic Monthly; April 2001; The Genetic Archaeology of Race - 01.04; Volume 287, No. 4; page 69-80.