by Kenneth W. Krause.
Kenneth W. Krause is a contributing editor and “Science Watch” columnist for the Skeptical Inquirer. Formerly a contributing editor and books columnist for the Humanist, Kenneth contributes regularly to Skeptic as well. He may be contacted at firstname.lastname@example.org.
“People, including me, would rather believe that significant human biological evolution stopped between 50,000 and 100,000 years ago, before the races diverged, which would ensure that racial and ethnic groups are biologically equivalent.”—Steven Pinker.
Pinker might be right about what most people would prefer to believe. But equivalency, I would argue, is a concept better left to mathematicians—should they choose to keep using it. In any other, less antiseptic context, however, the notion is utterly bankrupt. That we have had to work so hard in recent centuries to construct and maintain political equality among individuals and classifications of individuals should tell us how persistent and pervasive inequality really is. We should never confuse the social construct with the scientific reality. Denial is the least mature and, certainly, the least progressive response to fear.
Like all other species, human beings continue to change. But until very recently, both the popular and scientific assumptions had been that, if humans were still evolving at all, it was through the very slow and completely random process of genetic drift. The alternatives, natural and sexual selection, of course, turn on differential reproductive success based on fitness, attractiveness, or both. So the prevailing argument has long been that, because we civilized humans have for the most part managed to insulate ourselves from the natural environment, to nurse our sick back to health, and to provide mates for nearly all persons among us, the march of Darwinian selection had finally reached an impasse. Similarly, many have claimed that, because selection had long ago relaxed its discriminating grip on the human genome, our collective abilities to think and to resist disease, for example, have steadily degenerated.
But there have been exceptions—like University of California at San Diego biologist Christopher Wills, who in his 1998 book, Children of Prometheus, defiantly pronounced that “[t]he powerful effects of our culture have, if anything, accelerated our biological evolution.” Wills’ powerful and prescient hypothesis was that genes and an increasingly rich—or at least complex—culture have combined to create a positive feedback loop in which human minds in particular benefit from frequent adaptive boosts. Sure enough, recent genome projects and surveys along with new and controversial genetic studies seem to bear Wills out.
In 2005, for example, University of Chicago geneticist Bruce Lahn published a pair of studies concluding that two genes thought to regulate brain growth have continued to evolve under selective pressures until very recently, if not to the present day (Science 309, 1717-1720 and Science 309, 1720-1722). An intellectual controversy erupted because Lahn, a Chinese-born lifetime member of the NAACP, also discovered that these mutated alleles were less common among sub-Saharan Africans than in other populations.
Different mutations of the Microcephalin and ASPM genes were known to cause primary microcephaly, a positively dreadful condition marked by severely reduced brain size (typically 400 cubic centimeters in affected adults compared to 1200 to 1600 cubic centimeters in normal adults). It was also commonly understood that phylogenic analyses of both genes had revealed strong positive selection in the primate lineage leading to Homo sapiens. The question for Lahn, then, was whether certain variants of Microcephalin and ASPM had continued to evolve by natural selection during the last 200,000 years, since humans became anatomically modern.
After sifting through a vast cache of DNA broadly representative of global diversity, Lahn’s team located an allele for each gene that occurred so frequently that it simply had to have been adaptive rather than merely the stray product of genetic drift or group migration. Then, using past mutation rates as a reliable molecular clock, they estimated the dates when these alleles originated. Lahn determined that the Microcephalin variant arose only about 37,000 years ago (with a 95 percent confidence interval of 14,000 to 60,000 years) and, much to everyone’s amazement, that the ASPM allele clocked in at about 5800 years ago (with a 95 percent confidence interval of 500 to 14,100 years). Many, including Lahn’s team, noted that these dates generally corresponded to the explosion of symbolically driven behavior in Europe (the “Upper Paleolithic revolution”), on the one hand, and the development of cities and written language on the other.
But these studies ignited a firestorm of debate over race and intelligence because they concluded as well that these apparently beneficial variants were common in Eurasia (75 percent of some populations), but quite rare in Africa (less than 10 percent among some groups). Several researchers formally challenged Lahn’s findings of selection generally or of selection for various brain-related abilities in particular (See, e.g., Currat, M., et. al., Science 313, 172a ; Timpson, N., et. al., Science 317, 1036a ; and Rushton, J.P., et. al., Biol. Lett. 3, 157-160 ). But Lahn defended his work and reemphasized that he had never claimed to have demonstrated a cognitive purpose for these alleles (Science 313, 172b  and Science 317, 1036b ). He even conceded the remote possibility that their roles might implicate functions completely unrelated to the brain.
In any case, the new genes’ youth and worldwide prevalence clearly evidenced a “selective sweep”—the rapid spread of an advantageous new allele—very much reminiscent of the genetic adaptations that had allowed European adults during the early Holocene to digest milk lactose. Although LCT, the lactase gene, arose around 8000 years ago, it has subsequently spread to more than 80 percent of Europeans, but less than 28 percent of Africans—the latter of which to a large degree have still not adopted agriculture as a way of life. But for any kind of selective sweep to occur, the advantage or selective force of the new allele must be dramatic. Could it be, as Wills suggested back in 1998, that our genes and cultural circumstances were and, in fact, are collaborating to accelerate human evolution?
University of Utah anthropologists Henry Harpending and Gregory Cochran certainly count themselves among the growing number of scientists who think so. Many will recall their famous—in some circles infamous—2006 study on the natural history of Ashkenazi intelligence (J. Biosoc. Sci. 38, 659-693). There, they and collaborator Jason Hardy determined that the unusually high IQ scores of European Jews resulted from their forced and intense occupation of a particular professional niche between the 9th and 17th centuries that strongly selected for economic acumen. Unfortunately for the Ashkenazim, heritable diseases like Tay-Sachs and Gaucher’s accompanied these mutations.
But, by the end of 2007, Cochran, Harpending, and University of Wisconsin at Madison biological anthropologist, John Hawks, had published their analysis of DNA in the International HapMap Project, a mammoth survey of genetic distinctions among populations around the globe. After scrutinizing 3.9 million single nucleotide polymorphisms (SNPs) from 270 persons, the team concluded that “[t]he rate of adaptive evolution in human populations has indeed accelerated” during recent millennia, especially since the Ice Age ending roughly 10,000 years ago (Proc. Natl. Acad. Sci., USA 104, 20753-20758). The agricultural revolution initiating the Holocene epoch allowed certain Eurasian populations to explode, says Hawks, and for increasingly complex human cultures to flourish
As population densities increase, he adds, so do the opportunities for genetic mutation—favorable or otherwise. Indeed, the team found that a minimum of seven percent of the human genome appears to be evolving right now at the highest rate in our species’ history. But how can we know that some of these changes were adaptive? Geneticists look to haplotypes—large blocks of linked DNA passed on from one generation to the next—for helpful clues. An allele resulting from an important adaptive trait will expand to great frequency in a population so rapidly that it will often drag an extended haplotype with it before recombination and mutation can break it down. In other words, to population geneticists like Hawks, rare SNPs flanked by long stretches of identical DNA in many individuals among a given population strongly suggests recent and robust selection for an especially advantageous trait.
And such were precisely the attributes that Hawks’ researchers discovered in about 1800 human genes. Although scientists don’t know the identity or function of most of these genes, many appear to be responses to recent changes in diet and to new waves of virulent diseases, including AIDS, malaria, and yellow fever. Again, the agricultural revolution was the likely catalyst and, again, some populations were more affected than others. As Hawks notes, “sub-Saharan Africa has no archeological evidence for agriculture before 4,000 years ago,” and “[a]s a consequence, some 2,500 years ago the population of sub-Saharan Africa was likely < 7 million people, compared to European, West Asian, East Asian, and South Asian populations approaching or in excess of 30 million each.” Contrary to popular belief, Hawks concludes, humans on different continents appear to be evolving away from each other and at quite an impressive clip.
Now, a group of French and Spanish geneticists, led by Lluis Quintana-Murci at the Pasteur Institute in Paris, France, has reinforced the Americans’ results by identifying 582 genes that have evolved differentially in various world populations during the past 60,000 years (Nature Genetics 40(3), 340-345 ). Attempting to isolate disease-causing variations, Quintana-Murci examined the DNA of 210 persons from Phase II of the HapMap database, including 2.8 million SNPs from Europeans, Asians, and Africans.
Like Hawks, he found compelling indicators of recent positive selection that varied strikingly between geographic populations. An ENPP1 mutation, for example, which is known to protect against obesity and type II diabetes, is present in about 90 percent of non-Africans but nearly absent in Africans. A CR1 gene, by contrast, which is known to thwart malarial attacks, is virtually absent in everyone except Africans, who carry it at a rate of about 85 percent. But Quintana-Murci isn’t interested in any potential political implications. Rather, he expects his results to “open multiple avenues of research” and to “facilitate genetic explorations of medical conditions by identifying strong candidate genes for diseases in which prevalence depends on ethnic background.”
Even so, many scientists are still concerned about what some non-scientists will do with this information—and understandably so, given our history. On November 7, 2008, Constance Holden reported a meeting of about 40 scientists and ethicists at the National Human Genome Research Institute in an article titled, “The Touchy Subject of ‘Race’” (Science 322, 839). Although much debate has already ensued over the medical use of racial distinctions in disease-related alleles, “it won’t be long,” Holden predicts, “before [scientists] have solid leads on much more controversial genes: genes that influence behavior—possibly including intelligence.”
University of Georgia at Athens professor of speech communication, Celeste Condit, apparently criticized Lahn’s work at the meeting, charging that his studies could be seen as embedding a political message. Lahn denied the accusation and, according to Holden, rejoined that scientists have become “‘almost like creationists in their unwillingness to acknowledge that the brain is not exempt from selection pressures.” One could argue, in fact, that because the brain is affected by so many genes, it is uniquely situated to sustain adaptation.
The panel wisely agreed that we need to police our language to some extent, by opting for terms like “geographic ancestry” in lieu of “race,” for example. But I would insist that precision alone should drive our vocabulary, not fear of historical baggage or the specters of inappropriate popular inferences and political agendas. Although we surely must remain vigilant on behalf of universal political equality, neither social conservatives nor liberals can afford to keep ignoring the differences between populations at the molecular level.
If indeed culture is accelerating human evolution by means of natural selection, perhaps technology and the economic forces of globalism will one day in the very distant future meld many populations into one. But, until then—for our own benefit—we should let the scientific chips fall where they may. In his timely and thoughtful new book, Strange Fruit: Why Both Sides Are Wrong in the Race Debate (Oneworld, 2008), British author Kenan Malik acknowledged that the very concept of “race” is both unscientific and irrational. But so is the current practice of antiracism, he adds, which, on the one hand, tends to impose otherwise alien cultures upon minority individuals and, on the other, seeks to deny them important biological facts that might one day benefit them and their descendants in very profound ways. “We need to challenge both [concepts],” Malik urges, “in the name of humanism and reason.”