What Does Human Evolution Explain?
Nicholas Wade’s book may be the most unassuming brick I’ve ever seen thrown through an intellectual window. It might as well have been wrapped in a Magritte-esque note reading: “This is not a brick.”
It aims to smash through the conviction that racial differences are only skin deep. Progressively more sophisticated decodings of the human genome over the past decade have advanced our knowledge of human evolution, and contrary to the scientific conventional wisdom of a generation ago, evolution did not stop around the time of the last ice age. It may even have accelerated since then and continues today. The evidence that, as Wade puts it, “human evolution has been recent, copious and regional” piles up steadily but has not been absorbed into the popular consciousness. Wade’s book intends to change that.
The question is: is Wade’s book hard and heavy enough to break through? And is smashing windows really the best way to advance the cause Wade proclaims as his own—the advance of science and of popular understanding of science?
Many of the examples Wade cites should be familiar to those even peripherally conversant with the subject. Tibetans have a genetic adaptation that enables them to thrive at higher altitudes than are safe for most other peoples. This adaptation only became common in the Tibetan population in the past 3,000 years. (Though, interestingly, reports since the publication of Wade’s book suggest that the genes responsible for the adaptation may be the result of mixing with the Denisovians, a hominid population that went extinct millennia before but with which homo sapiens appears to have interbred.) Lactose-tolerance is a somewhat older but far more influential mutation, one that developed independently, and differently, in northern Europe and in Africa and which may be credited for the rapid advance of the Indo-European and Bantu language families.
Given that scientists have observed micro-evolution of this sort in nonhuman species within the lifetimes of individual researchers, and given the ample evidence from animal husbandry that both physical and behavioral traits can be altered in relatively short spans of time, these human evolutionary discoveries should not be surprising. Rather, they should be received as exciting new knowledge about our history, collective and individual. And so they frequently are: the same people who hold to the conventional wisdom about human evolution may well be among the throngs eager to use the new genomic history to trace their own ancestry. But we as a society have been extremely resistant to the implications—to wit, that human populations likely differ from one another in deep and important ways.
That resistance, says Wade, is based in a fear of recapitulating the horrors of the 19th and 20th centuries—from Social Darwinist arguments against provisions for the welfare of the poor to the forced sterilization of those deemed mentally unfit to the epochal crime of the Holocaust—that had been rationalized as improvements to the human gene pool. Wade assures the reader not only that he is similarly appalled by that history but that, in his opinion, our fears are largely unfounded. Science, pursued with proper integrity, will never prove the overall superiority of any one group, and taboos against racism do not require the promulgation of bad science. We can, he assures us, pursue the truth about human evolution without fear; there are no ugly political implications to the science of human evolution because there are no ugly political implications to any scientific finding. Our moral and political beliefs should stand or fall independent of the state of scientific knowledge about our origins.
But is that true? And whether it is or it isn’t, does Wade believe it to be true?
Color this reader skeptical. After walking through the scientific consensus on the course of human evolution since the exit from Africa, Wade proceeds, in the latter half of the book, to grand speculation about the course of human history, speculation that unquestionably implicates the sorts of political and moral questions that Wade earlier claims are not implicated by the science of human differences.
To pick the most obvious and least convincing example, Wade asserts a genetic basis for the tribalism that has undermined nation-formation in much of Africa and the Middle East, and he argues from this assertion that the Iraq War was predictably an act of folly since a modern Western democratic system could not simply be transferred to the tribal world of Iraq. Quite clearly, Wade does think there are moral and political implications to this science.
Now, the Iraq War was predictably an act of folly, and a modern Western democratic system could not simply be transferred to Iraq. But the assertion of a genetic basis for tribalism is neither necessary nor sufficient to make that case. As Wade acknowledges, societies can adapt in dramatically different ways from the same genetic substrate. Japan went from isolationism to openness and Westernization to fanatical nationalist militarism to quietistic consumerism and democracy, all within a century, without ever ceasing to be highly conformist, shame-based, and ethnocentric. And most importantly, Wade has no evidence for his contention that tribalism is hard-coded into some populations’ genes but not into others. To demonstrate that genetic differences were the crucial factor in political developments would require a level of knowledge about the genetic basis of behavioral differences that Wade knows we do not have, as well as the kind of robust ability to control for other factors that we are unlikely ever to have.
There’s a similar problem with some of the other genetically-based historical theories that Wade cites with approval. For example, he admires Gregory Clark’s argument that the Industrial Revolution occurred in England because of a change in the behavioral characteristics of the population. Throughout the Middle Ages, wealthy Englishmen had more children on average than those who were poorer; as a consequence, over the centuries a greater and greater percentage of the English population could trace their descent to those individuals who were able to acquire and sustain wealth. But why would a similar dynamic not have obtained in China, or Egypt, or Persia, other societies that were civilized longer, and lived closer to the Malthusian edge for longer, than England? There may indeed be important genetic differences between pre-agricultural peoples and the populations of long-settled civilizations, which would undoubtedly be worth exploring, but a great deal more genome-level work needs to be done to substantiate these hypotheses before jumping to conclusions about the course of human history.
Wade also spends many pages arguing the value of dividing humanity into continent-scale racial groups. Yet he is unable to keep to his continental scheme: he waffles on whether Northeast and Southeast Asians belong together and whether the Middle East, North Africa, and South Asia deserve separate classification. More to the point, he has put the taxonomic cart before the analytic horse: given his interest in explaining behavioral differences, what Wade should be doing is identifying distinct behavioral groupings and then investigating whether any of them exhibit common ancestry or parallel evolution of different adaptations, as with Tibetan and Andean adaptations to high altitude. That would give him a functional taxonomy. Instead, Wade starts with a “common sense” grouping of peoples and then tries to line this pre-existing taxonomy up with possible explanations for behavioral differences, many of which are themselves not very well defined.
Interestingly, one of the narrower hypotheses Wade discusses—Gregory Cochran, Jason Hardy, and Henry Harpending’s explanation for high Ashkenazi Jewish IQ—meets with somewhat less favor than broader theories like Clark’s. Their hypothesis is a somewhat complicated one: that the combination of a small founding population at the end of the Dark Ages and a narrow concentration in the profession of moneylending created powerful selection pressures on Ashkenazi Jews for high intelligence, and more specifically the kind of intelligence needed for symbolic manipulation as opposed to spatial manipulation. Apart from the observed difference in IQ, these scholars point to a group of Mendelian genetic disorders involving nerve growth that disproportionately affect Ashkenazi Jews; their hypothesis is that these diseases are an unfortunate byproduct of the same pressure.
The hypothesis is highly speculative—as Steven Pinker pointed out in a review of the Cochran-Hardy-Harpending hypothesis in The New Republic, it depends on a whole series of as yet unproven historical and biological sub-hypotheses being true, and any theory with so many vulnerable links will be slow to be accepted. But what the hypothesis has going for it, that many of Wade’s preferred theories does not, is a falsifiable causative link—not merely a correlation—between genetic mutation, a biological change, and a behavioral consequence.
Wade, however, finds the Cochran-Hardy-Harpending hypothesis too limited in scope and moves on to speculate that the requirement for literacy in rabbinic Judaism might have resulted in selection for intelligence—which, if true, might have implications on the course of evolution of other populations.
It’s a general weakness of Wade’s book: he prefers broad, sweeping speculation about the course of history to the careful building of a case from blocks of evidence. In this way, A Troublesome Inheritance ironically resembles one of its intended targets, Jared Diamond’s Guns, Germs, and Steel, which similarly extended discrete insights deserving of further investigation—like the importance of domesticable animals to the development of civilization—far beyond what they could plausibly explain.
This is a problem not only for how convincing Wade’s historical speculations are but for the case he makes that there are no moral or political implications of the science he is popularizing. If, as Wade appears to believe, the West is distinctly more creative than other civilizations and has that character because of genetically-based behavioral differences, that surely has implications for the moral validity of race-based conceptions of nationality. If, as Wade appears to believe, that character is due to what amounts to Social Darwinist dynamics in the Middle Ages, that surely has implications for the legitimacy of eugenic arguments today. Our moral commitments are rarely if ever entirely divorced from their practical consequences.
If Wade is right that differences between human populations are practically significant, then maintaining our convictions against the kinds of racial theories that were highly popular in the 19th and early 20th centuries will require more than hand-waving about how no group is uniformly superior to any other or how is cannot imply ought. We will need recourse to Abraham Lincoln’s imaginative sympathy in recognizing that while we are all quick to identify others as inferior, deserving of enslavement, none of us would happily submit to enslavement ourselves, even to someone obviously more powerful or intelligent than ourselves, and therefore the most important equality is an equality of moral concern. A recognition of natural inequality could fuel greater social solidarity rather than racism: in particular, it might be the basis for a pushback against the meritocratic fallacy that our reciprocal obligations are limited to fair treatment and an equal opportunity to compete.
As for eugenics, it would be well if Wade made the point more forcefully that there is no such thing as all-encompassing fitness. Breeding to maximize one trait inevitably sacrifices others. A key practical argument for diversity is that we don’t know what traits we will need; a key practical argument against eugenics is that we don’t know what traits we will lose. Moreover, our “common sense” conception of fitness is inevitably a product of our own—possibly genetically conditioned—preferences. But what we like best or are most comfortable with may well not be adaptive in the unknowable future.
It’s a shame that Wade spent so much of his book on theories of history when there are so many other areas where the science he touts could be of practical benefit. Medicine will be improved if we study the differential progress of disease and the effects of therapies on different populations. Psychology will be improved if we don’t assume that everyone on earth cognitively resembles American college students. Education will be improved if we study the distribution of learning styles in different populations and develop practical pedagogical adaptations.
This moment in the human sciences is exciting not because it promises yet another theory of everything to explain the world as it is but because of the myriad small advances in understanding that will help us individually adapt to our environment, and adapt our environment to us, to further human flourishing.
The assumption that all groups within the extended human family are essentially identical across all cognitive and behavioral categories is not a window to be smashed. It’s a wall in the path of progress. And bit by bit, as science reveals specific facts about how human populations vary from one another, that wall gets undermined, and a new one gets built, brick by brick. Meanwhile, we shouldn’t assume that the new edifice science builds will conform to what either our ideological predispositions or our common sense tells us must be so. We should prepare to be surprised. And keep a genuinely open mind.
Senior editor Noah Millman blogs at TheAmericanConservative.com/Millman.