Nicholas Wade followup, deeper dive edition

I’m very happy with the editing and fact-checking they did at Boston Review for my review of Nicholas Wade’s book, A Troublesome Inheritance: Genes, Race and Human History, and I don’t want to undermine their work (thanks to managing editor Simon Waxman and associate web editor Nausicaa Renner). If you only have time to read 4,000 words on it, their version is what you should read. It’s up here for free.

But in the thousands of words that ended up on the cutting room floor, there were a few ideas I’d like to post here, for the very interested reader.

Photo from Flickr Creative Commons by epSos.de

Human bones

A number of critics have said that Wade’s early chapters are good, and the book only gets crazy-racist in the second half when he starts attributing social behavior to races and tracing global economic disparities to evolution by natural selection. But I did want to stress that he’s got plenty wrong in the early part of the book as well. In particular, I highlighted the question, why did human bones get thinner in the millennia before they settled down? This isn’t something we worry over much, but I think it’s an important clue to his biases and assumptions. From the published review:

To establish that genes determine social behavior, Wade looks to ancient history, when humans first settled in agricultural communities. “Most likely a shift in social behavior was required,” he writes, “a genetic change that reduced the level of aggressivity common in hunter-gatherer groups.” Of course, many elements were involved—climate change and geography, population pressure, the presence of various plants and animals, advances in tools and weapons, and human biological evolution—but there is no evidence that a behavioral genetic change was required.

I actually spent a fascinating few hours reading the scientific literature on evolution and bone structure, and saw no mention of the reduction in human aggressive behavior as a cause of human bones becoming weaker. To elaborate, Wade thinks natural selection gave people genes for thinner bones because strong bones became less necessary for survival as people fought each other less. He thinks genetic change in behavior led to genetic change in bones. Please correct me if I’m wrong, but I don’t see any literature at all to back this up (Wade doesn’t cite any).

In fact, if I read it right, we might have thinner bones today than people did 50,000 years ago even though our bone genetics haven’t changed much, as a result of diet and lifestyle changes alone. How is that possible? When the bones of young people bear less weight they don’t grow as thick when they’re adults. This is the issue of tool use and the declining “habitual loads” on human limbs. It might also extend to our skulls because we’re not grinding pre-agricultural superfoods with our teeth all day long. Biological anthropologist Christopher Ruff writes: “In a few years, the strength of a person’s bone structure can change as much as the total average change over the past 2 million years of human evolution.” He cites classic research showing the bones of tennis players’ arms are thicker on the side they hold the racket. There is an alternative view that genetic adaptation did drive changes in bone size, having to do with climate change (here is some of that debate). But nothing about aggression I could find.

This point about the bones not-so-subtly underlies his later argument about Africa’s poverty, which he attributes in part to the genetic propensity toward violence among its people. Rather than aggression being an asset as society evolved, Wade speculates that, in the centuries leading up to the first settlements, “the most bellicose members of the society were perhaps killed or ostracized” (again, no evidence). Cue footage of UN peacekeepers landing in Africa.

Anyway, it’s potentially an important lesson in the malleability of human bodies through life experience rather than (only) through genetic change. The implication is that each generation may still be genetically ready to have thick bones again, but we just keep lucking out and being born into societies with tools and soft foods, so we don’t need to grow them. I find that amazing. I don’t want to push it too far, but I imagine that a lot of behavioral things are like that, too. Evolution has brought us to the point where we have vast potential to grow in different ways, and huge differences between people can emerge as a result our life experiences.

More on the “warrior gene”

In the review I included some discussion of the MAO-A studies:

Wade devotes considerable attention to MAO-A, the gene that encodes the enzyme monoamine oxidase A, which is related to aggression. He singles out studies showing that a rare version of the gene is associated with violence in U.S. male adolescents. Out of 1,200 young men surveyed in the National Longitudinal Study of Adolescent Health, eleven particularly violent young men carried the 2R version of MAO-A, subsequently known as the “warrior gene.” Nine of those eleven were African American, comprising 5 percent of the black male adolescents in the study.

Sometimes in genetics there is some gene or coding that produces some measureable effect, and that’s how most people seem to think about genetics most of the time – there is “a gene for” something. In the days before today’s genome-wide association (GWA) studies, before scientists had the means to investigate hundreds of thousands of genetic markers at a time, they often looked for effects of such “candidate” genes. This approach was valuable, especially when the role of specific genes was known (as in the case of the BRCA1 gene, associated with higher risk of breast cancer). However, with most diseases, and even more so with behavior, which is presumed to be more complicated than single-gene mechanisms, candidate gene studies were (are) often fishing expeditions, with a high risk of false-positive results, amplified by selective publication of positive findings. It is quite possible that’s at least part of what happened with MAO-A and aggression.

Most studies about MAOA have been gene-environment interaction studies, where some version of MAOA has a statistical association with a behavior only in the presence of a particular social factor, such as a history of child abuse (e.g., this one). This kind of study is tricky and offers a lot of opportunity to fish around for significant effects (which I’m specifically not accusing any particular person of doing). The MAO-A 2R studies he cites weren’t interaction studies. But a couple of cautions are important. First, that 2R version of MAO-A is very rare, and the two studies Wade cites about it (here and here) both used the same sample from Add Health – 11 boys with the variant. Two studies doesn’t mean two independent results. You could never get a drug approved based on that (I hope). Second, as far as I can tell there was no strong reason a priori to suspect that this 2R variant would be especially associated with violence. So that’s a caution. I have to say, as I did in the review, that it may be correct. But the evidence is not there (and you shouldn’t say “not there yet,” either). Those two studies are the entire evidentiary basis for Wade saying that genes that shape social behavior vary by race (“one behavioral gene … known to vary between races”.) I didn’t find any other studies that show MAO-A 2R varies by race (though maybe there are some).

 

Yao Ming and Ye Li

Modern evolution

Does natural selection still apply to humans? Of course. But I can’t see how it works very efficiently in modern societies, because our demography seems like a poor launching pad for genetic revolutions. Most threats to our survival now occur after we’ve had the opportunity to have children. And it’s getting worse (which means better). The decline in child mortality and the extension of life expectancy beyond the childbearing years means that relatively few people are left of out of the breeding community. That’s how I was raised to understand natural selection: individuals with stronger, better traits breed more than those with weaker, worse traits. In the U.S. today, 97.8% of females born live to age 40, and 85% of those have a birth, so 83% of females born become biological mothers. And a good part of modern childlessness is voluntary, rather than the consequence of a genetic weakness. Even as recently as 1900, in contrast, Census data and mortality statistics show that only 53% of females born lived to be age 40 and had a surviving child. So I don’t know how evolution is working today, but except for really bad health conditions I’m skeptical.

Of course, we have selective breeding producing subpopulations that have concentrations of genetic traits. Yao Ming’s parents were both basketball players, and his wife is 6′ 3″. So they’re on their way to producing a subpopulation of really tall Chinese people. But most social divides we have are not like that — they aren’t based on genetic traits. So I don’t see that being very effective either. To take Wade’s example of Jews and math ability (a chapter I didn’t write about because I was already 3,000 words long), you would need to have Jews not only have good math genes, and only reproduce with each other, but they’d also have to cast out those kids who were relatively bad and math and put the boys and girls who were relatively good at math together. That could happen, but it would be inefficient and very slow, and next thing you know some historical event or trend would come along and mess it all up.

Even the much-discussed increasing tendency of college graduates to marry each other — which gives us about three-quarters of couples today being on the same side of the college/non-college divide — is just sloppy and slow by selective-breeding standards. Maybe it could produce a race of people who like baby joggers and The Economist, but given the low levels of isolation between groups and the length of human generations I just think any progress in that direction would be so slow as to be swamped by other processes pushing in all different directions.

Australia

Wade used Australia to argue against Jared Diamond, whose account of world history, Guns, Germs and Steel, dismisses genetic evolution as an explanation, making him the villain in Wade’s story. How is it, Wade wonders, that Paleolithic Age native Australians were unable to build a modern economy, but Europeans could waltz onto the continent and be successful so easily? He writes:

If in the same environment … one population can operate a highly productive economy and another cannot, surely it cannot be the environment that is decisive … but rather some critical difference in the nature of the two people and their societies.

That’s one of the worst head-scratchers in the book. Does Wade really think that Europeans just dropped in to Australia on an equal footing with the local population, and had to figure out how to thrive there on their raw genetic merits, proving their superiority by their relative success? It can’t be that “the nature of the two people and their societies” means the boats, weapons, technology and modern state social organization the Europeans possessed, because then he has made Diamond’s point. So the “nature” he’s referring to must be genetics. To the reader who has a passing familiarity with modern social science, this is just jarring.

Does cancer genetics help?

To help show the dead-end of Wade’s very mechanical view of genetic influence, I drew out an example from cancer genetics (with a little help from my brother-in-law, Peter Kraft, who is not responsible for this interpretation).

What if we found that genetic factors contributed to social behavior in any of the ways Wade imagines? Speculative as that is at present, it is of course a possibility. Most people are concerned about the implications for genocide and eugenics, for good reason. But even if our scientific motives were pure, the functional utility of such information would be questionable.

Consider a comparison to the much better understood genetics of disease. Take prostate cancer, which is known to have a family history component. Genome wide association studies have identified some genetic markers that are significantly associated with the risk of developing prostate cancer, such that a genetic test can identify which men are at highest risk. However, a review of the statistical evidence in the journal Nature Reviews Genetics pointed out that, even among the high-risk group only about 1.1% of men would come down with prostate cancer in a five-year period. That’s much higher than the 0.7% expected in the general population, but what do you do with that information? Invasive procedures, medications, or preventative surgery on millions of men would not be worth it in order to prevent a small number of cases of prostate cancer – the side effects alone would swamp the benefits. On the other hand, we don’t need any genetic tests to tell smokers to quit, or urge people to eat better and exercise.

This is just one example. Risk factors for this and other diseases are the subject of intense research, and there are actionable results out there, too. But I suspect that genetic influences on social behavior, if discovered, would present an extreme version of this problem: slight genetic tendencies implying tiny increases in absolute risks – and interventions with huge costs and side effects – all while more effective solutions stare us in the collective face.

To complete the analogy: In other words, if – big if – we could identify them, should we incarcerate, surveil, or segregate a subpopulation with a small increased odds of committing crime – thereby preventing a tiny number of crimes while harming a large group of innocent people? And should we isolate and elevate the children of some other subpopulation because of their slightly higher odds of success in some endeavor? Or should we instead devote our resources to improving education, nutrition, employment and health care for the much larger population, based on the well-established benefits of those interventions? We know lots of effective ways to affect social behavior, including against “natural” inclinations.

I’m really not against scientific exploration of behavioral genetics. But the risk of exaggerated results and inflated importance seems so high that I doubt the research will be useful any time soon.