When my colleague Corinne Purtill bought her doll-loving daughter an engineering kit, she had to laugh when the then-three-year-old used the present as a hairbrush. For all Corinne’s efforts at gender-neutral parenting, her daughter clearly enjoyed some traditionally feminine toys.

A study published (paywall) in November 2017 suggests that these sorts of girly toy preferences aren’t simply a reflection of gendered social pressures. A meta-analysis of research, reviewing 16 studies on the subject that collectively included some 1,600 children, found that both biology and society affect boys’ and girls’ toy choices. The researchers found a huge effect size (1.03 for boys playing with boys’ toys more than girls, and 0.9 for girls playing with girls toys more than boys; anything above 0.8 is considered “large”) across geographical regions.

“The size of sex differences in children’s preferences for male-typed and female-typed toys did not appear to be smaller in studies conducted in more egalitarian countries,” says Brenda Todd, a study co-author and senior lecturer in psychology at City University London. Countries rating extremely low on the Gender Inequality Index, such as Sweden, showed similar differences in toy preferences to countries with far greater gender inequality, such as Hungary and the United States.

This runs counter to the popular narrative that gender differences expressed in childhood play are determined entirely by social expectations. Social factors certainly do have influence, and the paper found evidence of this: For example, as boys got older they were increasingly likely to play with conventionally male toys, reflecting the impact of environmental rather than biological causes. But overall, the data reflect broader findings in psychology, which show that biology and society interact to cause gendered behavior. In other words, contrary to the popular progressive belief, gender is partly socially constructed—but it’s not just a social construct.

“The ‘nature versus nurture’ idea is a false dichotomy”

“The ‘nature versus nurture’ idea is a false dichotomy,” says Sean Stevens, social psychologist and research director at Heterodox Academy, an organization of professors focused on promoting political diversity in academia. “I don’t know any real researcher of human behavior who would say it’s all nature or all nurture,” he adds.

Despite this empirical truth, researchers who study the biological basis of gender often face political pushback. “Many people are uncomfortable with the idea that gender is not purely a social construct,” says Todd, who notes that her work has faced “very critical attention.” There’s a political preference—especially on the left—Todd believes, for gender to be only a reflection of social factors and so entirely malleable.

Evidence that gender has some basis in biology, though, in no way implies a strict gender binary, nor negates the existence of transgender and non-binary identities. Many biology-based gender differences originate from the hormonal environment within the womb, which is very different on average for boys compared to girls. But there’s a huge variation in these environments, says Alice Eagly, psychology professor at Northwestern University. “Within boys there will be a range and within girls there will be a range. To say it’s biological doesn’t mean it’s perfectly binary,” she says.

The findings of this and other studies suggest biology influences gendered behavior. It remains unclear how large these differences are—regardless of whether they’re caused by social or biological factors. Janet Hyde, a psychology and women’s studies professor at the University of Wisconsin-Madison, has conducted several meta-analyses on the subject, and found relatively small behavioral, intelligence, and personality differences between genders. (The biggest difference she found was in incidence of masturbation.) Certainly the differences are not as stark as those reinforced by gendered cultural norms, and do not reinforce old-fashioned stereotypes about men being inherently better at math and more angry or arrogant than women. Differences that do exist, though, whether caused by social or biological factors, deserved to be studied from a scientific perspective rather than ignored for the sake of a political narrative.

Broadly speaking, there’s far too little specific evidence on what gender differences are influenced by biology to extrapolate into justified policy for any company or industry. And, the evidence for a biological basis for gender certainly doesn’t mean we should be complacent in the face of sexism; society and culture, too have a massive effect on gender. Neurogeneticist Kevin Mitchell neatly sums up this argument in a tweet:

Eagly argues that policy should not influence science. “Science strives for valid findings, the truth of the findings, regardless of whether you like them or I like them. We strive to find out how the biology of people works. Would we close our minds as scientists because it might be politically incorrect?,” she says. How the evidence could influence policy is not up to her, she adds. “I’m not a social policy expert,” says Eagly.

“Science strives for valid findings, the truth of the findings, regardless of whether you like them or I like them.”

That said, these scientific findings can certainly be used to positive effect. “If we have a better understanding of how biology impacts the developing brain, we might be better able to tailor educational practices to specific students,” says Stevens. In other words, nurture can be manipulated so that it more effectively interacts with nature to develop particular skills. If we ignore biology, says Stevens, “we’re not acknowledging that there might be another factor impacting things and then we wonder why things aren’t as effective.”

So what does the biology of gender mean for parents deciding whether or not to encourage their kids to play with less gender-conforming toys? Corinne’s daughter is now seven and loves Lego, science, space, fashion, art, makeup, and singing. Regardless of which of those preferences are influenced by biology and which by social factors, she’s clearly an individual rather than a reflection of a tired gender stereotype. Corinne says she’s noticed her 18-month-old son loves wrestling and climbing more than his sister did. But these differences do not affect equality in her household.

“The toys, clothes, colors, and games my kids like are their business,” she says. “What I will insist is that everyone in the house does chores equally. Everyone in the house will be raised with respect for other people and their boundaries. Both kids will be raised to be self-sufficient adults who can advocate for themselves.”

Gender may not be an entirely social construct. But the effects of biology do not confine us to traditional gender norms. And there’s no science that counters the value of gender equality.