I got a lot of feedback from Race, Genetics and Taboo. Mostly positive, believe it or not. One particularly engaging e-mail conversation was with Jonathan Tweet, author of the fantastic evolutionary children’s book Grandmother Fish. A lot came out of these dialogues worth sharing with the world. In any case, it’s my responsibility as a geneticist. Just as educators need to speak openly about safe sex despite it being an uncomfortable topic, so it is with race. Thus, even though I maintain that other species are more interesting, here I am writing again about (human) race and genetics.

It has often been noted that black people perform worse than white people, on average, on various standardized tests. Naturally, racists love to jump on this statistic as evidence for genetic interracial racial differences in cognitive ability. And of course, their logic is faulty. The scientific method says that you can’t infer a genetic effect between two groups when you haven’t controlled for environmental factors. I’m not even going to get into whole question of what IQ is, or whether IQ tests actually measure important neurological characteristics accurately.

It should be a no-brainer that blacks and whites experience the world differently on a day-to-day basis thanks to, well, racism. But does that explain the tests? After all, we still see an effect after controlling for things like income and geography. In fact, we see an effect called regression to the mean. Basically, children of parents with unusually low IQ tend not to have such extreme IQ, but are closer to the mean value for their race. The same goes for children of atypically smart parents. Is this as evidence that IQ differences between races are due to genetics? Nope. Here’s why.

Part of the problem is the oversimplicity of the phrase “nature vs. nurture.” The word “nurture” implies parental care. It leads us to think that the non-genetic effects are mostly attributed to “how you are raised.” But this isn’t the case. A good discussion of the topic can be found in Stephen Pinker’s The Blank Slate. Pinker points out that variation in parenting has little effect on variation in the behaviors and abilities of our offspring. Instead, most non-genetic effects are due to the greater environment: our peers, the media, cultural whisperings, and seemingly trivial chance experiences.

This article, for example, makes the bizarre claim that regression only matches a genetic model. But regression to the mean is a basic statistical property of nearly all types of data. It is certainly not unique to genetics. The article implies that children of high IQ parents should have both good “nature” (genes) and good “nurture” (parenting), so they should match their parents’ IQs. But that makes no sense. Even smart, well-off parents can’t shield a kid from racism. Children are still going to learn behavioral expectations from their classmates, stories, and random strangers, and those will impact their performance. So cultural factors can also explain regression to the mean. In any case, there are genetic factors that explain differences in IQ among people. These just don’t measurably differ among races. But they still will contribute to a regression to the mean phenomenon: a randomly selected person will have an IQ that is similar to the IQ of his or her close relatives, but closer to the mean.

If someone tried to pass off this kind of inference on any other species, their colleagues would roll their eyes. Imagine that there are feral dogs and pet dogs in my town, and they form distinct genetic populations because Lady-and-the-Tramp-type romantic scenarios are rare. Say I discover that feral dogs take longer to learn a task. I could not publish a paper claiming a genetic basis for this learning difference. More likely, something about the experience of being a feral dog affects the ability to be trained. But there would be variation in both groups, and some feral dogs would be quick learners. Suppose I found that feral puppies from fast-learning feral dogs regressed back down toward the feral dog mean. That would be perfectly compatible with the feral-pet difference being cultural, not genetic. If I really wanted to test it, I’d need to raise dogs side by side in a common garden experiment. Otherwise, concluding that it’s genetic would be a great way to get my paper rejected from any reasonable journal.

So the human data are compatible with either genetic or cultural effects. Still, you may ask, isn’t it plausible that the genetic explanation is correct, even if we can’t prove it? Sure, it’s possible, but it’s not very likely. From first principles, any geneticist should be skeptical of a genetic basis for racial IQ differences, because the trend is opposite from what you should expect. Quantitative geneticists are very familiar with heterosis, or hybrid vigor: genetically diverse organisms usually show greater health, growth, and fitness. This phenomenon is seen in numerous animals and plants. Most species, including humans, have two copies of their genome, one from each parent. If the two copies of a gene are different from each other, that can have two beneficial consequences. First, it’s less likely that both will be broken in the same way and produce to some harmful effect. And second, it’s more likely that the two different copies will act synergistically and provide higher fitness than either one would alone. African Americans have higher genetic diversity than European Americans for two reasons. One, the ancestors of Europeans underwent a genetic bottleneck when a relatively small number of them left Africa. And two, most African Americans have both European and African ancestry, so they possess variants from both continents at many regions of their genomes. So if heterosis played a meaningful role in human intelligence, it would not favor whites. If anything, one would expect black Americans to have higher IQs than white Americans. The fact that the observed pattern is in the other direction suggests that it has nothing to do with genetics.

Still, couldn’t there be some slight genetic difference? Maybe. But not like you think. Even if some measurable genetic difference were found, it would not be an explanation for anything important to society. It would not be the cause of differences in crime rates or educational achievement among races. It would not be the reason that Europe is more developed than Africa. It would not explain the dearth of melanin in the average Nobel Prize winner. Humans behavior is too complex, too plastic, too responsive to culture. The cognitive and psychological difference between a modern human and their own direct ancestor a thousand years ago is vastly greater than between that person and their neighbor of a different race. This comic is about sex differences, but a similar point could be made about race.

Remember, “scientific” racism is a pseudoscience. Like astrology. Astrologists claim that your birth month determines all sorts of essential personality characteristics. They have no evidence for this. A very careful analysis could theoretically reveal such an effect, perhaps due to your relative age compared to most of your classmates. But so what? I can confidently say that any such effect is much smaller than what a typical astrology buff believes. It’s certainly not an overarching driver of who you are. And there is no reason to assume that any such differences would line up with astrological predictions. So it is with race. Racist claims are similarly nonsense, not science. Give them the no more credence than the assertion that aliens built the pyramids. But don’t ignore them. Address them. Unchecked, they are dangerous.