And though cognitive development is obviously a big deal, there’s plenty of social conditioning, here: Go into any toy store—the girls’ side is lousy with pink brooms and kitchen accoutrements, dolls and other products of domesticity. The boys’ side, in contrast, is blue and red, action-oriented, building materials and science projects. (Never mind that the number of hours women work outside the home has almost tripled since 1965, while the amount of hours men spend on housework and childcare hasn’t increased at remotely similar rate. Probably a coincidence.)

Let Toys Be Toys, a U.K. campaign for gender-neutral toys, has had some success in pushing retailers to drop gender-based toy marketing, but their wins are far from comprehensive—and frankly, we’re nowhere near the tipping point at which criticism for gender-based toy marketing will prove compelling to most major American retailers.

Here’s what’s particularly confounding: These hard-and-fast gender rules for toys is a relatively new phenomenon. Or, rather, it’s a return the bad old days. For decades, toy production and marketing was increasingly gender neutral. Then, at some point over the last few years, things changed.