IMAGINE walking into the toy department and noticing several distinct aisles. In one, you find toys packaged in dark brown and black, which include the “Inner-City Street Corner” building set and a “Little Rapper” dress-up kit. In the next aisle, the toys are all in shades of brown and include farm-worker-themed play sets and a “Hotel Housekeeper” dress.

If toys were marketed solely according to racial and ethnic stereotypes, customers would be outraged, and rightfully so. Yet every day, people encounter toy departments that are rigidly segregated — not by race, but by gender. There are pink aisles, where toys revolve around beauty and domesticity, and blue aisles filled with toys related to building, action and aggression.

Gender has always played a role in the world of toys. What’s surprising is that over the last generation, the gender segregation and stereotyping of toys have grown to unprecedented levels. We’ve made great strides toward gender equity over the past 50 years, but the world of toys looks a lot more like 1952 than 2012.

Gender was remarkably absent from the toy ads at the turn of the 20th century but played a much more prominent role in toy marketing during the pre- and post-World War II years. However, by the early 1970s, the split between “boys’ toys” and “girls’ toys” seemed to be eroding.

During my research into the role of gender in Sears catalog toy advertisements over the 20th century, I found that in 1975, very few toys were explicitly marketed according to gender, and nearly 70 percent showed no markings of gender whatsoever. In the 1970s, toy ads often defied gender stereotypes by showing girls building and playing airplane captain, and boys cooking in the kitchen.

But by 1995, the gendered advertising of toys had crept back to midcentury levels, and it’s even more extreme today. In fact, finding a toy that is not marketed either explicitly or subtly (through use of color, for example) by gender has become incredibly difficult.

There are several reasons gender-based marketing has become so prevalent. On a practical level, toy makers know that by segmenting the market into narrow demographic groups, they can sell more versions of the same toy. And nostalgia often drives parents and grandparents to give toys they remember from their own childhood.

Such marketing taps into the deeply held beliefs about gender that still operate in our culture; many parents argue that their daughters and sons like different things. This is particularly true for boys: parents tend to stick with gender-typed toys for boys, either because they understand that the social costs for boys who transgress into the “pink” zone are especially high in a homophobic culture or because of their own desire for gender conformity.

This becomes a self-reinforcing cycle: as toys have become more and more gender segregated, the social costs of boundary crossing and the peer pressure to stay within the lines are huge, for kids and parents alike.

But if parents are susceptible to the marketers’ message, their children are even more so. In a study on parental toy purchases led by the psychologist Donna Fisher-Thompson, researchers who interviewed parents leaving a toy store found that many bought gender-typed toys because their kids had asked for them, and parents were a bit less likely to choose gendered toys — at least for girls — on their own.

Moreover, expert opinion — including research by developmental and evolutionary psychologists — has fueled the development and marketing of gender-based toys. Over the past 20 years, there has been a growth of “brain science” research, which uses neuroimaging technology to try to explain how biological sex differences cause social phenomena like gendered toy preference.

That’s ridiculous, of course: it’s impossible to neatly disentangle the biological from the social, given that children are born into a culture laden with gender messages. But that hasn’t deterred marketers from embracing such research and even mimicking it with their own well-funded studies.

For example, last year the Lego Group, after two decades of marketing almost exclusively to boys, introduced the new “Friends” line for girls after extensive market research convinced the company that boys and girls have distinctive, sex-differentiated play needs.

Critics pointed out that the girls’ sets are more about beauty, domesticity and nurturing than building — undermining the creative, constructive value that parents and children alike place in the toys. Nevertheless, Lego has claimed victory, stating that the line has been twice as successful as the company anticipated.

The ideas about gender roles embedded in toys and marketing reflect how little our beliefs have changed over time, even though they contradict modern reality: over 70 percent of mothers are in the labor force, and in most families domestic responsibilities are shared more equitably than ever before. In an era of increasingly diverse family structures, these ideas push us back toward a more unequal past.

This article was reposted from NYTimes.