Stretch Genes

1.

Science and science journalism are different things. Though each is valuable, they require at least partly different skills. Science demands unrelenting skepticism about purported facts and theories, and science journalism demands an ability to make the complex clear. Despite my admiration for his work as a journalist, I’m afraid that Nicholas Wade’s latest book reminds us of the risks inherent in blurring the distinction between these endeavors. A Troublesome Inheritance goes beyond reporting scientific facts or accepted theories and finds Wade championing bold ideas that fall outside any scientific consensus.

Wade, now a freelance writer and reporter, is best known for his work as a journalist at The New York Times. He has also written several popular books on biology. The most recent–Before the Dawn (2006) and The Faith Instinct (2009)–focused on evolution in human beings, including the evolution of religion. In A Troublesome Inheritance, Wade maintains this focus on human evolution, though he turns to a far more controversial topic, human races. His goal, he says, is “to demystify the genetic basis of race and to ask what recent human evolution reveals about history and the nature of human societies.” He concludes not only that human races are real but that they probably differ genetically in surprising ways.

Wade’s main claim is that human races likely differ in social behavior for genetic reasons as a result of recent evolution. These slight differences in behavior may, in turn, explain why different sorts of social institutions appear among different peoples:

Institutions are not just sets of arbitrary rules. Rather, they grow out of instinctual social behaviors, such as the propensity to trust others, to follow rules and punish those who don’t, to engage in reciprocity and trade, or to take up arms against neighboring groups. Because these behaviors vary slightly from one society to the next as the result of evolutionary pressures, so too may the institutions that depend on them.

Evolutionary biology might therefore have something to say about why some peoples live in modern states and others in tribal societies, and why some nations are wealthy while others remain mired in poverty.

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A Troublesome Inheritance cleaves neatly into two parts. The first is a review of what recent studies of the genome reveal about our evolution, including the emergence of racial differences. The second part considers the part that genetic differences among races may play in behavior and in the social institutions embraced by various races. These two parts fare very differently.

2.

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As people dispersed about the planet, they ultimately settled into the five great “continental races”: Africans (sub-Sahara), East Asians, Caucasians (Europe, the Indian subcontinent, and the Middle East), Australians, and Native Americans. Some of these groups are younger than others (America was peopled only in the last 15,000 years), but this division provides, Wade says, a reasonably realistic portrait of how human genetic diversity is partitioned geographically. Because of their geographic isolation from one another, these groups of human beings necessarily evolved mostly independently over the last tens of thousands of years. During this period of independent evolution, much of what we think of as characteristically human arose, including agriculture and settlement in permanent villages.

So what has study of the human genome over the last decade revealed? Wade’s chief conclusion here is that human evolution has been “recent, copious and regional.” The facts are fairly straightforward. The continental races of human beings differ somewhat from one other at the level of DNA sequence. As Wade emphasizes, these differences are “slight and subtle” but they can nonetheless be detected by geneticists who now have access to many genome sequences from around the planet.

The central fact is that genetic differences among human beings who derive from different continents are statistical. Geneticists might find that a variant of a given gene is found in 79 percent of Europeans but in only, say, 58 percent of East Asians. Only rarely do all Europeans carry a genetic variant that does not appear in all East Asians. But across our vast genomes, these statistical differences add up, and geneticists have little difficulty concluding that one person’s genome looks European and another person’s looks East Asian. To put the conclusion more technically, the genomes of various human beings fall into several reasonably well-defined clusters when analyzed statistically, and these clusters generally correspond to continent of origin. In this statistical sense, races are real.

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Wade’s survey of human population genomics is lively and generally serviceable. It is not, however, without error. He exaggerates, for example, the percentage of the human genome that shows evidence of recent natural selection. The correct figure from the study he cites is 8 percent, not 14, and even this lower figure is soft and open to some alternative explanation. And Wade generally assumes that evidence of selection reflects adaptation to the ecological environment, whereas some events might reflect the action of other evolutionary forces like sexual selection, in which individuals compete for mates, not for survival.

Worse, Wade says that biologists realized only in the last few years that natural selection might change a trait by causing slight changes in the frequencies of variants at many genes instead of a large change in frequency at one gene. In fact, the former hypothesis is the traditional view of evolutionary change and is nearly a century old. It would be unfair to suggest that these sorts of mistakes undermine Wade’s main claims in the first part of A Troublesome Inheritance. But they do suggest that he is not the surest guide to a technical literature.

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3.

In the latter half of A Troublesome Inheritance, Wade ventures into far more controversial territory. His claims are, in outline, simple enough.

As human beings evolved over the last tens of thousands of years, the genetic basis of people’s behavior may have changed, just as the basis of their skin color did. Some of these changes may have resulted from Darwinian adaptation to new forms of social life. For example, the “Great Transition” from nomadic life to permanent settlement that began some 15,000 years ago likely produced a profoundly altered social environment: populations grew larger, people interacted with more non-kin, and society became more hierarchical.

In response to this new environment, social behaviors may have changed by natural selection. In some societies, people who were less aggressive or more trusting, for instance, might have prospered under these conditions. {snip}

Crucially, Wade says that “evolution in social behavior has necessarily proceeded independently in the five major races,” reflecting their geographic and thus genetic isolation. The net result of all of this, during settlement as well as other events in recent evolutionary history, is that the continental races might well come to differ genetically in social behavior.

To Wade, the implications are big. While behavioral differences among races would surely be subtle, they can, he insists, become amplified at the level of entire societies. Slight differences in behavioral predisposition–to cooperation, aggression, trust, propensity to follow rules, and so on–probably pushed different races in directions that led to different social institutions. Indeed the “seeds of difference between the world’s great civilizations were perhaps present from the first settlements.”

Wade devotes much of his book to showing how this evolutionary thesis can help explain all manner of differences among peoples. These include why some peoples are tribal and others modern (modern life requires, among other things, extending trust to non-kin), why some are violent and others less so, why some are poor and others rich, why some are innovative and others conformist, and so on.

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Wade also thinks that “evolutionary differences between societies on the various continents may underlie major and otherwise imperfectly explained turning points in history such as the rise of the West and the decline of the Islamic world and China.” Here, and especially in his treatment of why the industrial revolution flourished in England, his book leans heavily on Gregory Clark’s A Farewell to Alms (2007). Across these historical turning points, the details differ but the story remains the same: certain peoples were predisposed genetically to behaviors and thus institutions that paved the way for their success, whether, say, economic (the West) or intellectual (the Jews). Other peoples, alas, had other genes.

These are big claims and you’d surely expect Wade to provide some pretty impressive, if recondite, evidence for them from the new science of genomics. And here’s where things get odd. Hard evidence for Wade’s thesis is nearly nonexistent. Odder still, Wade concedes as much at the start of A Troublesome Inheritance:

Readers should be fully aware that in chapters 6 through 10 they are leaving the world of hard science and entering into a much more speculative arena at the interface of history, economics and human evolution.

It perhaps would have been best if this sentence had been reprinted at the top of each page in chapters 6 through 10.

One of the most frustrating features of A Troublesome Inheritance is that Wade wants to have it both ways. At one moment, he will concede that he writes in a “speculative arena” and, at the next, he will issue pseudofactual pronouncements (“social behavior, of Chinese and others, is genetically shaped”). This strategy lets Wade move in a kind of intellectual no-man’s-land where he gets to look like he’s doing science (so many facts about genomes!) while covering himself with caveats that, well, it’s all speculative.

Which might lead you to wonder: If Wade has little or no hard evidence for his evolutionary thesis, how does he hope to convince his readers to take it seriously? Part of the answer is by offering captivating narratives about how recent human evolution could have played out, as we saw earlier with the transition to permanent settlement. Wade also makes several arguments based on plausibility for the role of genes in behavioral differences among the races and, to a lesser extent, attacks those who have doubted such a role.

One of Wade’s main plausibility arguments involves the difficulty of transferring social institutions from one group of people to another. As he puts it, “one indication of such a genetic effect is that, if institutions were purely cultural, it should be easy to transfer an institution from one society to another.” As we’ve learned, this isn’t always true. For example, “American institutions do not transplant so easily to tribal societies like Iraq or Afghanistan.” And that, it seems, is that. We are to conclude that the differences are probably partly genetic.

This argument is remarkably feeble. Suffice it to say that when we attempt to transfer an institution, say free elections, into another culture, we do not replace one entire culture with another. Instead, we transfer a piece of a culture into an existing one. Is anyone really surprised that this process causes friction? And is it really most plausible to conclude that the source of this friction is differences in genes? What about all those other differences–in history, language, distribution of wealth, religion, educational attainment, ravages of war, arable land, resentment toward perceived invaders, and so on? Among these factors, I suspect that genes are perhaps the one most similar between American and Afghan societies. This isn’t to say that Wade’s argument is necessarily wrong but it is to say that an important feature of a plausibility argument is plausibility.

Another of Wade’s plausibility arguments focuses on stability: “When a civilization produces a distinctive set of institutions that endures for many generations, that is the sign of a supporting suite of variations in the genes that influence human social behavior.” Really? Shouldn’t Wade say that stability “might” be a sign of genes? It’s true that some behaviors or institutions may persist for partly genetic reasons. (Milk-drinking by adults requires lactose persistence, a genetic trait that is more common among cultures that engaged in dairy farming historically.) But it’s also true that some behaviors or institutions persist for purely cultural reasons. The English have used a currency called the “pound” since Anglo-Saxon times. And Western music has been built on a diatonic scale since the Renaissance and probably much earlier. So why doesn’t Wade conclude that differences in currency and musical scale reflect differences in genes?

Conversely, it’s hard to see why profound instability in social institutions doesn’t trouble Wade more. He’s much taken, for instance, with the difference between tribal and modern societies, but one of the most tribal peoples on the planet, the Scots with their clans, are now identified with some of the most modern of ideas and attitudes. Were David Hume and Adam Smith precocious carriers of a mutation that swept Edinburgh?

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Wade obviously appreciates the distinction between behavior that “could be” genetic and “is” genetic. The problem is that he doesn’t seem particularly interested in hard evidence or even in the prospects that relevant hard evidence could ever be obtained.

There is, however, another distinction that Wade doesn’t seem to appreciate at all. He’s right that political sensitivities shouldn’t distort scientific truth: the facts are the facts. But as Pinker notes, this doesn’t mean that we shouldn’t be particularly careful when discussing race. History has shown that this is an especially dangerous subject, one that has resulted in enormous abuses. There is nothing unscientific about recognizing this and treading carefully.

At times, Wade’s approach seems almost the opposite. Though he issues the requisite disclaimers about the dignity and moral equality of all peoples, he’s clearly tempted, under the cover of politics-shouldn’t-distort-science, to provoke. Indeed there is a species of bravado here, as though demonstrating that he, unlike others, is tough-minded enough to face unpleasant facts. But surely there is a difference between facing facts that are unpleasant and spinning tales that are improbable.