Allen Orr, my first Ph.D. student, has developed a thriving career as a popular book reviewer, and in this week’s New York Review of Books, he critique’s Nicholas Wade’s new book, A Troublesome Inheritance: Genes, Race, and Human History.
I made a few comments on this book a few days ago, saying that it was in the main pretty bad, though one part, the presentation of the case for genetic differentiation of human populations, was not too bad. But Wade’s main thesis was that differences between human societies, as well as rapid changes within human societies, was due to evolutionary change mediated by natural selection. That latter contention, I claimed, had no evidence behind it, though Wade argued otherwise. I did not, and do not, recommend that you read the book.
I’m pleased to see that in Orr’s review, “Stretch genes,” he says pretty much exactly what I thought, though much more incisively. Here are some quotes from his piece:
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.
…..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.
This is what I also claimed, and of course got slammed by the race-denialists who are motivated largely by politics. To a biologist, races are simply genetically differentiated populations, and human populations are genetically differentiated. Although it’s a subjective exercise to say how many races there are, human genetic differentiation seems to cluster largely by continent, as you’d expect if that differentiation evolved in allopatry (geographic isolation). As Orr notes:
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.
Finally, Orr takes the book to task for its big claims about the genetic underpinnings of human social differences, which are unsubstantiated:
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.
This is the problem with Wade’s book: it presents a sweeping hypothesis about the selective basis of human social differences ( a touchy subject), but gives virtually no evidence to support it. If you like stories, it’s fine; if you like science, it’s not so fine. Wade sometimes offers disclaimers, but the reader’s impression will be that he really is presenting scientific findings. It’s an bad piece of scientific journalism, and the next-to-last paragraph above sums up the problem neatly.
By all means read Orr’s review at the link above (it’s free), but I can’t say I’d urge readers to buy the book. It might read okay to those who don’t know a lot about evolution, but to an evolutionary biologist, or a sociologist who knows about genetics as well as the cultural malleability of societies, it is a frustrating and ultimately irresponsible book.