In 2015, Morning Consult did a survey on attitudes toward nuclear power, and according to reporter Davis Burroughs, nuclear reactors "face pronounced unpopularity among an unexpected bloc: women."

This is not unexpected at all: polls and surveys have consistently found a wide gender gap on nuclear power, going all the way back to the 1970s. Though overall public support for nuclear waxes and wanes, the gender gap stays steady. Said Gallup in 2012:

Men and women have sharply different attitudes about nuclear power, differences that are larger than those found between partisan, ideological, age, and educational segments of the population. Men favor nuclear power as a source of electricity by a 72% to 27% margin. But 51% of women oppose it, with 42% in favor. The same large gender gap exists in terms of views of the safety of nuclear power plants.

Other surveys have found slightly different numbers, but almost always a spread in the 20- to 40-point range.

This question has been of intermittent interest to researchers for decades, but only recently have they begun honing in on a plausible answer.

The tl;dr version of the research: several hypotheses have some backing in the literature; out of the common explanations, one has been all but disproved and one has been repeatedly confirmed, though it's more complicated than it appears at first blush.

Is it because women know less about nuclear?

Many nuclear advocates, confronted by the gender gap, posit a simple explanation: women know less about nuclear power. After all, the science and engineering fields generally, and the nuclear industry specifically, are dominated by men. Women are socialized at an early age to avoid those fields (though that may be changing). Consequently, this hypothesis goes, they don't know as much, and what they don't know, they fear.

This would be convenient explanation for nuclear advocates, but it turns out not to be true. Study after study has examined the "knowledge gap" hypothesis and found that it doesn't hold up. A comprehensive review of the literature from 1996 put it bluntly: "One hypothesis, the expectation that increased knowledge will lead to decreased concern, has received so little support, despite repeated examination, that it can be discarded."

Is it because women are more liberal or environmentally conscious?

Another hypothesis points to the roles women are socialized to play — homemaker, protector of family and children — as the source of their concern about nuclear power. A related hypothesis points to the values, like nurturing and the importance of community, that women are socialized to prioritize. These more theoretical explanations, which arise from gender studies, are difficult to measure, but each has found some support.

Or maybe it's because women are more liberal? After all, there's been a gender gap in partisanship for decades, as well, with women more likely to support activist government and assistance for children and the elderly. But that doesn't explain why the gender gap disappears on more general energy questions, or questions about renewable energy.

Maybe women care more about the environment? The data here is mixed. Some surveys have found this to be true; others have found no (or very small) gender difference. Almost all surveys find that levels of environmental activism are actually lower among women, though that may reflect social and economic constraints more than levels of concern. What seems to be the case is that on general, abstract environmental questions, the gender gap declines or disappears, while on questions of specific environmental risks it increases.

Is it because women assess risk differently?

That last bit hints at the hypothesis that has proven most robust: that men and women assess risk differently. Women appear more sensitive to specific, local risks across the board. In that literature review I mentioned earlier, researchers say:

We were able to locate 17 studies providing relatively direct test of [the risk-sensitivity hypothesis]; not a single study contradicted it, and none of the 17 so much as failed to find a significant effect in the expected direction.

You see the same phenomenon crop up in surveys on other issues. For instance, out of this survey of attitudes on land use, the New York Times put together this graphic:

As you can see, the gender gap is particularly large on nuclear plants, but it replicates itself in every case where the development might pose some threat to the local community. (Note how the gap all but disappears on wind energy.)

Is it because white men assess risk differently?

But wait! It's more complicated than that. This famous 1994 survey found that the gender gap around environmental risks is only true among white people; it disappears among nonwhites. "Most striking," write the researchers in that study, "was the finding that white males tended to differ from everyone else in their attitudes and perceptions — on average, they perceived risks as much smaller and much more acceptable than did other people." This survey was the source of the "white male effect," much studied in the social sciences ever since. (This 2000 survey found something similar.)

If it is white males at issue, then the cause is probably not any inherent or biological difference between men and women. In fact, a recent literature review (and re-analysis) by Julie Nelson has dented if not destroyed the notion that there are deep, generic differences between the genders on risk perception. In fact, these effects vary widely based on circumstance and experimental design. The "risk-averse female" archetype now so common in economics probably reflects deep-seated social and gender assumptions more than research.

In short, the real gap on nuclear power is not between men and women, but between white men and everyone else. And this has far more to do with socialization than with any inherent or biological differences.

Is it because conservative white men assess risk differently?

A 1994 study called "Gender, Race, and Perception of Environmental Health Risks" concludes with some speculation:

Perhaps white males see less risk in the world because they create, manage, control, and benefit from so much of it. Perhaps women and nonwhite men see the world as more dangerous because in many ways they are more vulnerable, because they benefit less from many of its technologies and institutions, and because they have less power and control.

That sounds about right. In fact, Yale's Dan Kahan (familiar to Vox.com readers) led a study showing that the differences in risk perception were almost entirely a function of what he calls "identity-protective cognition" among a very particular set of white males. It's not so much a "white male effect," he says, as "a 'white hierarchical and individualistic male effect' reflecting the extreme risk skepticism of men with those worldviews."

White hierarchical individualistic males were motivated to resist claims of environmental and certain other risks, we conjectured, because the wide-spread acceptance of those claims would justify restrictions on markets, commerce, and industry—activities important (emotionally and psychically, as well as materially) to the status of white men with those outlooks.

The conjecture, he says, has held up in the face of subsequent evidence.

So we've narrowed in here. What looked like a gender divide on nuclear power is in fact mostly a function of the "extreme risk skepticism" of "white hierarchical and individualistic" males. (In the US, "white hierarchical and individualistic" males generally go by the more economical "conservatives.")

What other risks do conservative white men assess differently?

As it happens, there's another risk downplayed by conservative white males in service of identity-protective cognition: climate change. A 2011 study found that "conservative white males are more likely than other Americans to report climate change denial" and speculated that "the heightened system-justification tendencies of political conservatives" was responsible for the "high level of climate change denial in the United States."

So what are you saying?

In the name of heading off at least a few of the outraged emails I'm sure to receive about this, let me head off a few misunderstandings.