Modern humans, particularly of the historic Western Civilization variety, are typically a non-confrontational, go-along-to-get-along bunch. There’s a limit, sure, but by and large we tend to avoid difficult truths in large part because we don’t want to hurt feelings. And if we have any reason whatsoever to believe a comfortable lie rather than a difficult truth, we’ll choose the lie almost every time.

One influential view, often described as a “blank slate” conception of human nature, holds that differences between people are overwhelmingly shaped by environment rather than biology. There is an understandable appeal to that idea: If disparities are primarily the product of upbringing, institutions, or culture, then changing those conditions could change the outcomes. Biology is less accommodating.

Some traits are influenced by genetics, and genetic influences cannot simply be legislated away. To make broad assumptions based on immutable characteristics has become one of the greatest “sins” of the current cultural order. In terms of polite discussion, allowances can be made for race-specific genetic diseases or obvious biological differences between populations and sexes, probably because the lie would be too absurd to be believable. However, discussions about group differences in intelligence, especially what might cause them, have long been among the most taboo of all taboos.

The mentality is understandable. Nobody wants to think their limitations, or the limitations experienced by their group more broadly, may be the result of something they have zero control over. If external factors are holding us back, they can be identified, opposed, and even legislated against. If our own behavior or culture is holding us back, we could conceivably change those things and reach a better place. If it’s our own genetics, though, there’s not much to be done except work with what we have.

Political arguments about disparities tend to emphasize different explanations. Progressives often place greater weight on historical discrimination, institutional barriers, and continuing socioeconomic inequalities. Conservatives, by contrast, are more likely to emphasize family structure, individual behavior, culture, and other factors operating within communities. Both sets of explanations can matter.

What receives considerably less attention is the possibility that biological differences could also contribute to some observed differences between populations. That possibility does not make biology the only explanation, nor does it establish that any particular disparity is genetic. It simply raises a question that should be examined rather than declared off-limits.

Both external and internal factors can certainly contribute to disparities, and addressing them may narrow the gap somewhat. Measured IQ scores also differ substantially across countries and environments, underscoring just how important nutrition, education, health, and culture can be.

So, in a way, they are all correct to some degree, but not exclusively. Whether racial IQ gaps in the United States will ever close completely is impossible to know. The scientifically serious question is what proportion, if any, of observed group differences can be attributed to genetic rather than environmental causes.

It’s obviously a touchy subject all around, so it’s important to provide as much evidence and precision as possible before examining the social consequences of making any explanation effectively unspeakable.

First, average differences in measured IQ between racial groups in the United States have repeatedly been observed. The more contentious question is why those differences exist. An American Psychological Association task force report published in 1996 reported a black-white difference of roughly one standard deviation at the time and concluded that the gap could not simply be dismissed as an artifact of biased test construction or socioeconomic status. Crucially, however, the task force also said the available evidence did not establish a genetic explanation.

The first question, therefore, is relatively straightforward: Do average........

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