But evolution pays great heed to mutations that make a significant change to a gene and its protein. If the change is adverse, the mutations are ruthlessly eliminated because the affected individual either dies or fails to reproduce. If the change enhances the individual’s reproductive success, the mutation is selected for and becomes commoner in a population. These two kinds of selection, one negative and the other positive, are the two faces of natural selection. Biologists do not yet understand what genes need to be changed to make one species into two subspecies. However, it seems that the alleles involved in differentiating the human population are likely to be of the selected kind, not the neutral kind.
Versions of the two brain genes that evolved within the last 40,000 years show just this pattern. As mentioned in chapter 5, an allele of one, known as microcephalin, appeared some 37,000 years ago and is now widespread among Caucasians and East Asians but is much less common in sub-Saharan Africans. The FST for this allele between sub-Saharans and the others is 48% or 0.48, “which indicates strong differentiation and is significantly higher than the genome average of 0.12,” writes Bruce Lahn of the University of Chicago, who discovered the allele.241
A new version of another gene, ASPM, arose some 6,000 years ago in Caucasians, 44% of whom now carry this allele. The allele is less common among East Asians and rare to nonexistent in sub-Saharan Africans. The FST for the allele between Caucasians and everyone else is 0.29.242 There doubtless exist alleles of other brain-related genes, yet to be discovered, that are more common in East Asians or sub-Saharans and rare among Caucasians.
Most of the diversity in human skin color, for example, exists between populations, not within them. The FST for skin color is 88%, according to a study by John Relethford of the State University of New York at Oneonta.243 Skin color is heavily correlated with latitude as well as race, but clearly does not follow the pattern of the neutral genes. Henry Harpending and Alan Rogers suggest that “other visible traits that most humans notice are more like skin color than they are like neutral traits”—in other words that most of the physical characteristics on which people judge a person’s race are likely to be selected, just as would be expected if sexual selection has been the major force differentiating the human population.244
It is a few selected genes, not the many neutral ones, that may account for the differences between continental races. Substantial evidence for this idea has now emerged from a genomewide survey by Jonathan Pritchard of the University of Chicago. Devising a test to identify genes under recent selective pressure, he found roughly 200 such genes in Africans, in East Asians, and in Europeans. Each race’s set of selected genes overlapped very little with those of other races, just as would be expected if the populations on each continent had adapted independently to evolutionary pressures.363
Genotype and Phenotype among Races
Even if geneticists can see a difference between races at the level of DNA, what practical difference does that make at the level of the physical person? Biologists make a useful distinction between the genotype and phenotype of an organism. The genotype is simply the genome or hereditary information; phenotype is the physical creature that is generated from the genotype.
Because so much of the genome is nonworking DNA that does not code for genes, it is possible for genotype to vary without causing much change in phenotype. The Icelanders whose genotype can be matched to the island’s 11 regions probably don’t look any different from each other (although a survey is under way to see if they have a slightly different pattern of disease).
The work of Risch and Feldman showing that people can be genetically assigned to their continent of origin—that is, race—is based on genotype, and does not in itself indicate how much people of different racial genotypes might differ in phenotype. However, the sites on the genome that they examined move around during recombination (the shuffling of blocks of DNA that occurs between generations) in the same way that genes do. So some of these sites, especially those that lie close to genes, will be proxies for the genes themselves.
Thus the fact that people can be assigned to racial groups based on sampling just a few hundred sites in their genome suggests that quite a large number of genes may also vary between races and that so may the phenotype influenced by such genes. Races certainly vary in physical appearance. Nor are the differences just skin deep; there are also variations in susceptibility to disease and in the response to drugs.
The overarching similarity of all races is just what would be expected, given that the ancestral human population existed only 50,000 years ago, and given that human nature must to a great extent have been molded before the ancestral dispersal, since all its principal features are found universally. Proof of the continuing unity of the human family is that people of different races have no difficulty in interbreeding, and that the members of any one culture can, absent discrimination, function in any other.
But the existence of considerable variation between races should not be any surprise either, given that the human family has long been split into separate branches, each of which has evolved independently for up to 50,000 years or more, buffeted in different directions by the random forces of genetic drift and the selective pressures of different climates, diseases and societies.
Study of racial variation is not yet a scholarly pursuit, except in the area of medicine, and even there is not without controversy. Physicians who study racial disparities in medicine are well aware that many social attributes, such as poverty or lesser access to health care, track along with race. These factors, just as often as genetics, may be the explanation why African Americans, say, suffer a greater burden of certain diseases than white patients. But to ignore race altogether, as some argue should be done, would blind researchers to many findings of value, both social and genetic. A physician cannot tell if his black patients receive worse health care than whites unless he has first noted which race they belong to.
As for genetic contributions, BiDil would never have been discovered if Jay Cohn had not analyzed the response of African American patients to the drug. The discovery of an important drug for an underserved community might seem unalloyed good news. Nonetheless, some African Americans greeted BiDil with a distinct lack of enthusiasm because of a wider concern. These spokesmen fear that if African Americans are defined genetically, even for the benign purpose of medicine, the public may associate them with less reputable attributes, such as propensity to crime. “If you think in terms of taxonomies of race, you will make the dangerous conclusion that race will explain violence,” Troy Duster, a sociologist at New York University, said in objecting to race-based medicine.245
Understandably enough, any suggestion of a genetic basis for racial differences can engender strong passions. Disputes have long swirled around intelligence tests, which at present show differences between the various races of the United States. There is broad overlap between all populations but in terms of average score, Asian Americans come out somewhat higher than people of European ancestry, while African Americans score lower. While this fact is generally accepted, there is little agreement as to the reason. Some psychologists claim that IQ tests measure general intelligence, which they believe is in substantial degree inherited, and that the tests predict performance in later life. Others see the tests as evidence only of differences in education and other cultural advantages, and deny that any genetic explanation is applicable. This dispute, whose merits lie beyond the scope of this book, has long made the study of race controversial.
A less vexed instance of racial differences is provided by sports records. Some 95% of the top times in sprinting are held by West Africans, or African Americans who trace their ancestry to West Africa, according to Jon Entine. Entine, a filmmaker, made a documentary about black dominance of sport and then wrote a book, Taboo, so called because of the obloquy rained down on anyone who suggests a genetic basis for any aspect of race. West Africans’ dominance of sprinting is so complete that “all of the thirty-
two finalists in the last four Olympic men’s 100-meter races are of West African descent,” Entine writes.246
In middle distances, of 5,000 to 10,000 meters, it is not West Africans but men from Kenya in East Africa who dominate. Kenyans hold the top 60 world times in the 3,000-meter steeplechase and more than half the top times in the 5,000 and 10,000 meters. Within Kenya, most of these winning runners are Kalenjin speakers of the Great Rift Valley region, particularly a small population called the Nandi. The Nandi, who comprise less than 2% of Kenya’s population, have produced half of Kenya’s Kalenjin-speaking athletes and 20% of all the winners of major international distance running events.247
Interestingly, the Kenyans have tried to extend their domination of the middle distance to the sprint, but with serious lack of success: the best Kenyan time in the 100 meter sprint ranks about 5,000th on the all-time list.248 This suggests they possess some quality of specific relevance to middle-distance running.
Entine notes the many social factors that have helped determine dominance in sports, at least in the past. Basketball in the 1930s was dominated by Jewish players, and the sportswriters who speculated about some Jewish genetic suitability for the game were way off base. But many sports, particularly track events, are now much more open to all comers, regardless of race or social background. Despite the hard training and other factors that make a great athlete, there is likely to be some genetic component behind the spectacular dominance of West African athletes in sprinting and East Africans in middle distance events, in Entine’s view. John Manners, an author of books on Kenyan runners, also favors a genetic explanation for the prowess of the Kalenjin athletes whose record, he asserts, “marks the greatest geographical concentration of achievement in the annals of sport.”249 The Kalenjin, martial Nilotic pastoralists from Ethiopia, have lived for centuries at altitudes of 2,000 meters or more and marry mostly among themselves. They have a particular custom that could have acted as a genetic selection mechanism favoring strong runners, Manners writes. It has to do with cattle-raiding, of which the Kalenjin were for a long time the leading practitioners.
While some might call that theft, the Kalenjin regarded their actions as repossession of property that was theirs by divine right but had inadvertently fallen into others’ hands. The repossession procedure often required journeys of more than 100 miles so that the livestock could be far away before their ex-custodians realized their loss. “The better a young man was at raiding—in large part, a function of his speed and endurance—the more cattle he accumulated,” Manners writes. “And since cattle were what a prospective husband needed to pay for a bride, the more a young man had, the more wives he could buy, and the more children he was likely to father. It is not hard to imagine that such a reproductive advantage might cause a significant shift in a group’s genetic makeup over the course of a few centuries.”250 As Manners emphasizes, this is a speculation, not a proof, as to how the Kalenjin got to be so fleet of foot.
International sports events are an effective way of showing up even slight differences between races, and between ethnic groups within races, because of the way that physical characteristics tend to be distributed in a population. Most members of a population are of average height, very few are of dwarf or giant stature. If one population is very slightly taller than another, the difference might hardly be noticeable in comparing average members of each population. But if you hold a competition for the ten tallest people, all 10 may come from the slightly taller population since in this case it is the extreme, not the average, that is being compared.
The fact that different races or ethnic groups tend to excel at different sports—Africans at track, Chinese at ping pong, Europeans at weight-lifting—is not proof in itself of any genetic component but just a starting point that hints at possible genes to look for.
Genes versus Geography
Even though the individual members of every race may be much the same, human societies differ considerably in their levels of technology and organization. Some societies, like those of New Guinea, are just emerging from Stone Age cultures, while others, like those of Finland or Taiwan, are highly educated and lead in manufacturing sophisticated goods for the global economy. Is the difference solely because New Guineans were dealt a bad hand in terms of geography and resources, or could there be some genetic difference, maybe in the nature of sociality, that helped keep New Guineans and others in the Stone Age while propelling other peoples on a quite different trajectory?
Jared Diamond of the University of California, Los Angeles, has advocated a geographical answer to this question. In his book Guns, Germs, and Steel he argues that because more domesticatable species of plant and animal existed in Eurasia, agriculture got started there first, giving Europeans a head start in economic development. Accustomed to living in crowded environments, Europeans built up immunity to many diseases, including those contracted from their domestic animals, such as influenza, measles and smallpox, and these diseases were devastating to nonurban peoples on other continents.
In Diamond’s view, it was the economic head start and the germs, not any inherent difference in abilities, that enabled Europeans to conquer other peoples. “History,” he says, “followed different courses for different peoples because of differences among peoples’ environments, not because of biological differences among peoples themselves.”251
As Diamond explains, having spent many years studying the birds of New Guinea, he came to know the inhabitants well and was impressed with their evident intelligence. This led him to doubt the findings of the IQ testers in America, where “numerous white American psychologists have been trying for decades to demonstrate that black Americans of African origins are innately less intelligent than white Americans of European origins.”
In fact, New Guineans, in Diamond’s view, are probably more intelligent than Westerners, and the reason, he says, is genetic. The chief selective pressure on Westerners was the need to acquire resistance to the disease rampant in their crowded communities, whereas in New Guinea, where the chief cause of death is war, murder or starvation, one needed one’s wits to survive: “Natural selection promoting genes for intelligence has probably been far more ruthless in New Guinea than in more densely populated, politically complex societies, where natural selection for body chemistry [that is, immunity to disease] was instead more potent,” Diamond explains. And hence, “in mental ability New Guineans are probably genetically superior to Westerners.”
But if the New Guineans had the smarts, why was it the dumber, disease-ridden Westerners who figured out how to escape from the deadening cycle of Stone Age tribalism and perpetual warfare, a problem the New Guineans never cracked? Because Westerners lucked out in their geography, Diamond argues. Eurasia had a greater absolute number of plant and animal species and more of them proved suitable for domestication. Because species are adapted to climatic zones, domesticated crop plants and animals could be shared along lines of latitude, enabling Europeans to assemble packages of agricultural species and get a head start on the farming revolution. This advantage, slight enough 10,000 years ago, steadily accumulated to the point that by AD 1500 great civilizations had arisen in both halves of the Eurasian land mass, while much of the rest of the world had yet to clamber out of tribalism and illiteracy.
The Chinese then lost their technological edge, also for a geographical reason, in Diamond’s view: the connectedness of the Chinese mainland allowed one ruler to dominate and make irreversible errors, like destroying the Chinese fleet, whereas in Europe, with its balkanization and competing statelets, diversity thrived and the best idea had a better chance of winning out. By colonial times, this left Europeans as the winners, thanks to their superior geography.
Single cause explanations generally make historians roll their eyes but the boldness and ingenuity of Diamond’s thesis certainly puts geography more on the map than it was before. Yet does genetics have no role at all in shaping human history?
Many readers who like t
he political implications of Diamond’s thesis—that Western dominance is an accident of geography and therefore no race is better than any other—may skip over his premise of New Guinean genetic superiority. But if New Guineans adapted genetically by developing the intellectual skills to survive in their particular environment, as Diamond says is the case, why should not other populations have done exactly the same?
In attributing western advance solely to geography, while tacitly excluding the genetic explanation invoked for the New Guineans, Diamond focuses on the development of agriculture. But, as noted in chapter 7, archaeologists now believe that in the Near East sedentism came long before agriculture: first people settled down, abandoning the foraging way of life. Then they took to cultivating wild plants. Then, probably by accident, they developed domestic varieties of plant and animal species. The critical step was not domestication, but sedentism. This finding would seem to undercut an important part of Diamond’s case because, unlike the case with agriculture, it’s harder to see any geographical reason why sedentism should have risen in one society and not another. Given that the human form was undergoing another genetically driven change around this time, the gracilization of the skull and skeleton, a genetic explanation for sedentism would not be so implausible. People such as the Natufians perhaps responded to their environment with a different kind of sociality that enabled them to abandon the foraging way of life and settle down in fixed communities.
If sedentism was indeed prompted by an evolutionary change, it was one that may have occurred independently in different populations, as has happened with properties like pygmy stature, lactose tolerance and doubtless many others.
Such genetic adaptations, if they occurred, could not spread through the world’s population like wildfire, since it can take many generations for gene frequencies in a population to change. Instead, they would take place at different rates in different populations. This wide spread in start times for the forager-settler transition could help explain why human societies throughout the world have attained such different levels of development.
Before the Dawn: Recovering the Lost History of Our Ancestors Page 24