When I was a kid, I was obsessed with the He-Man and the Masters of the Universe cartoon. I had nearly all of the action figures, as well as a plastic Castle Grayskull. My best friend Phillip, conversely, had Skeletor's Lair, and our parents would often kindly help us drag those back and forth whenever we went to each other's houses to play.

At that point in the early 1980's, He-Man figures were about as stereotypically 'boy' as toys got – enough so that He-Man creator Filmation subsequently spun out the parallel She-Ra: Princess of Power to drive similar sales of toys to little girls.

Some of my other toy choices – from GI Joes to Tonka trucks and Matchbox cars – were similarly gendered. Yet I also often carried them around the house in my mother's old patent-leather purse, perhaps a bit less of a gender-normative choice. As my parents were good Baby Boomer Bay Area liberals, they did everything they could to avoid reinforcing sexist or gendered ideas about toys, or careers, or anything else.

Thirty-some years later, it seems that concern has spread well beyond the Palo Alto "quiche & Volvo" set. I see most of my parent friends around the country – and, indeed, even my own brother a few blocks away from me with his 18-month-old son Dylan – similarly trying to be thoughtful about the potentially sexist messages they send to their children. (You can spot a similar national-level concern in the plot of the last half-dozen Disney films: “the princess doesn't need to wait for a prince to rescue her; she can rescue herself!”) Yet, unavoidably, nearly all of those kids seem to eventually begin to steer themselves towards certain stereotypical toy-sets nonetheless.

Obviously, there's a large role for culture here – and even for the messages parents unconsciously send to their children. But there is, at the same time, a reasonable 'nature plus nurture' question: are there ways in which some aspects of things like gendered toy-choice might be more deeply biologically engrained?

I was thinking about that recently, in the holiday toy-buying run-up, and was therefore glad to discover two great studies in the world of our close primate relatives.

First, in 2009, a research team led by Janice Hassett of the Yerkes National Primate Center at Emory reported on experiments in which they followed toy preferences in a group of 34 juvenile rhesus monkeys. One by one, they let the monkeys go into an outdoor play area that had both a “masculine” toy (eg., a truck, a car, a construction vehicle) and a “feminine” toy (eg., a Raggedy-Ann doll, a koala bear hand puppet, a teddy bear), and camera-tracked the behaviors exhibited.

Long story short, the monkeys closely paralleled human children, with male rhesus monkeys clearly preferring wheeled toys over plush toys (using them more frequently, and for longer duration), and with female rhesus monkeys spending more time with the plush toys (though also, like human girls, spending substantial time with the wheeled ones; research has long shown girls are more open to ‘cross-gender’ toys than boys are).

Hassett’s team concludes there appear to be “hormonally organized preferences for specific activities that shape preference for toys.”

That lines up well with a parallel paper from Sonya Kahlenberg of Bates and Richard Wrangham of Harvard, which followed the Kanyawara chimpanzee community in Uganda for 14 years, cataloguing how they interacted with play objects. They observed that juvenile female chimps would carry around small sticks for hours at a time while they engaged in other daily activities (like eating, sleeping, and walking) in a manager suggestive of rudimentary doll play. While the same chimps used sticks as tools for specific purposes, the researchers were unable to discern any practical reason for the doll-stick carrying.

Ultimately, and after observing a bunch of related behavioral changes (i.e., females stopped stick-carrying when they had real babies), they concluded that “sex differences in stick-carrying are related to a greater female interest in infant care, with stick-carrying being a form of play-mothering (i.e. carrying sticks like mother chimpanzees carrying infants).”

So, there you go. As with any other topic involving gender, genetic disposition, etc., this one’s fraught with caveats, dangers in over-generalization, etc.

But, if nothing else, I do feel a little less guilty about buying Dylan an awesome Chanukah-gift truck set.

(Though, if they can find it somewhere in a box in their garage, I’d also suggest my parents dig out that old purse. It would be totally perfect for carrying around those trucks.)