Monkeys Playing With Boys and Girls Toys: One for the Annals of Really Bad Research

I've been known to be critical, perhaps overly so, of the media's bad science reporting, because it's, well, bad. But what is the media to do when the science itself is really bad? Since my advice to the media (which no one in the media has actually read, of course) is usually to listen to scientists, I don't really have an answer to that question, because when there's bad science, there's a scientist doing it. If the media listens to that scientist (and it's his or her work, so why wouldn't they?), they're probably not going to know it's bad science, even when it's really bad, as in the case of the study I'm about to describe (really, really, really bad). I suppose they could contact other scientists who are not involved with the research, and ask them about it, but that means finding a person who's not only read the study, but also works in an area close enough to that of the study to actually be able to evaluate it. And that's just too much work when you have deadlines.

Inevitably, then, we'll get bad science reporting that's not actually the fault of reporters. Like this (via Omni Brain), which can also be found here (via Ozarque). The article reports on this study by Gerianne Alexander and Melissa Hines. First, what does the press article say? Things like this:

Just like human boys and girls, male monkeys like to play with toy cars while female monkeys prefer dolls, a research project has shown.

This intriguing discovery is one of many signs of deep-rooted behavioral differences between the sexes that scientists are exploring with the latest tools of genetics and neuroscience.

Where did the reporter get this idea? From Alexander, who is quoted in the article as saying things like:

The differences apparently date far back in evolutionary history to the time before humans and monkeys separated from their common ancestor about 25 million years ago, said Gerianne Alexander, a psychologist at Texas A&M University in College Station, who led the experiment published in the journal Evolution and Human Behavior.

and

"Vervet monkeys, like human beings, show sex differences in toy preferences," Alexander wrote in the report. "Sex-related object preference appeared early in human evolution."

Alexander speculated that females of both species prefer dolls because evolution programmed them to care for infants. Males may have evolved toy preferences that involve throwing and moving, skills useful for hunting and for finding a mate.

Now that's some pretty provocative stuff! Though the paper was published in 2002, the press articles are pretty timely, coming soon after Larry Summers' remarks about his daughters' behavior upon being given toy trucks to play with. The findings would seem to confirm Summers' generalization from his own experience. When a scientists says something that bold, based on findings he or she has published, I feel duty-bound to go check out the paper itself. So I did. And in it the claims are no less provocative. Take this, from the abstract:

The results suggest that sexually differentiated object preferences arose early in human evolution, prior to the emergence of a distinct hominid lineage. This implies that sexually dimorphic preferences for features (e.g., color, shape, movement) may have evolved from differential selection pressures based on the different behavioral roles of males and females, and that evolved object feature preferences may contribute to present day sexually dimorphic toy preferences in children.

Wow! I don't know about you, but I can't wait to read more. But before I get to the experiments themselves, consider the motivation. The problem the paper is attempting to address is this: why do human boys and girls tend to prefer different toys, as several previous studies have shown? There are two general classes of answers: the essentialist position, which says that gender is largely biological, or based on genetic differences interacting with the environment (including culture); or the constructionist position, which says that gender is largely cultural, or a product of socialization. Based on the quotes above, Alexander and Hines obviously lean towards the essentialist position. And I have to applaud them for their choice of approach. If they were Evolutionary Psychologists, they'd have done a survey, but as actual scientists, they adopted a comparative approach. The idea behind the study, then, is that if gender differences in preferences are due largely to evolved differences in gender roles, then we might find similar preferences in other primate species, because they exhibit similar differences in gender roles. So they look at another primate species.

Here's what they did. They picked six different toys based on previous research on male and female preferences in human children. Two of the toys are "masculine" toys (an orange ball and a toy police car), two are "feminine" (a human baby doll and a red cooking pot) and two are gender neutral (a stuffed toy dog and a picture book). Fourty-four male and 44 female vervet monkeys were then individually presented with each toy in two or three sessions (the first being used to familiarize the monkeys with the toys). Each item was presented by itself, for five minutes, to each monkey in each trial. The experimenters recorded the number of times each individual approached the toys, and the number of times they came into contact with them (which counts as playing with the toys).

Consistent with the prediction of their essentialist hypothesis, the male vervets played with the ball and the car more than the female vervets, and the females played with the doll and pot more than the males. Furthermore, dominant males played with the "masculine" toys more frequently than less dominant males, and less dominant males played with the "feminine" toys more frequently than the more dominant males. Here are the graphs from the paper (from Figure 1, p. 471):


So it's pretty straightforward, right? Boy monkeys like boy toys, and girl monkeys like girl toys. The findings lead Alexander and Hines to conclude:

Our data suggest that this interest varies with the sex of the animal and across sex-typed toy categories derived from empirical studies (Berenbaum & Hines, 1992; Connor & Serbin, 1977; Maccoby & Jacklin, 1974) of sex differences in children's object play. Children's toys, therefore, appear to have differential value for males and females of at least two primate species, vervets and humans. (p. 473-474)

and thus:

In view of this evidence, our findings suggest that object features or functions associated with human sex-typed toy categories may have adaptive significance for males and females. In addition, evolved, specialized recognition systems for these object characteristics may direct object preferences in some primate species. (p. 474)

But before we get all excited, let's take a step back. First, we need to take a closer look at the data. Notice that it's in percent of total contacts. This is because male vervets had many more "contacts" than females. We don't get the absolute data, though, so we can't tell whether males actually played with the female toys less often, or just at a lower frequency relative to their overall amount of playing. Furthermore, males appear to have played with the two "masculine" toys and the cooking pot, a "feminine" toy, with about the same frequency, and with the furry dog only slightly more than these three. They played with the baby doll less than the two "masculine" and other "feminine" toys, but about as frequently as they played with the picture book. So it appears that, with the possible exception of the doll, the males didn't really care whether the toys were "masculine," "feminine," or "neutral." Do only female vervets have specific sexual preferences for toys (objects)? That's not what the authors concluded, but it would be hard to say otherwise based on their data, wouldn't it?

And then what about the toys themselves? The "feminine" toys include a baby doll and a red cooking pot, and the "masculine" toys an orange ball and a police car. Wait a minute, a cooking pot and a police car? What the hell do these have to do with evolved gender roles in vervet monkeys (putting aside, for a moment, the same questions about a human baby doll and a ball)? I suppose one could argue that cars have been designed to appeal to men, and thus have masculine forms (though I recall reading several years ago that the engineers at Jaguar based their body designs on the female body), but a cooking pot? It's shape is a product of cultural evolution, designed to afford holding the to-be-cooked substance, and handling without coming into contact with the part directly exposed to the heat. But vervets don't cook! So what is it about the pot that could possibly be consistent with vervet gender roles? Vervets don't drive, either, so the same question could be asked about the police car. And as Katherine noted in the comments at Omni Brain, there were two types of dolls, a dog and a human baby, neither of which are of the same species as the vervets, so why would they prefer one over the other (do they perceive the human doll as more like vervets than the dog doll? that's an empirical question that their data does not address)? The male vervets appear to have preferred the dog, while the female vervets played with both dolls about equally. What does that mean? I don't know, but I do now that it's more than a bit of a stretch to say that it means "that object features or functions associated with human sex-typed toy categories may have adaptive significance for [male] and [female]" vervets.

Given these problems, what do the authors have to say about the specific object preferences? For the female preferences, they write:

Female rhesus monkeys have been found to show a preference for the characteristic "reddish-pink"’ facial coloration of infant vervets compared to yellow or green. Consistent with this female color preference, girls are also more likely than boys to prefer warmer colors (i.e., pink and red) to cooler colors (i.e., blue and green) (Minamoto, 1985 cited in Iijima, Arisaka, Minamoto, & Arai, 2001). A preference for red or reddish pink has been proposed to elicit female behaviors to infants that enhance infant survival, such as contact (Higley, Hopkins, Hirsch, Marra, & Suomi, 1987). The hypothesis that reddish pink or red may be a cue signaling opportunities for nurturance and thus eliciting female responsiveness could explain our finding of greater female contact with both the doll (with a pink face) and the pot (colored red). (p. 475)

And for males:

Toys preferred by boys, such as the ball and police car used in this research, have been characterized as objects with an ability to be used actively (O'Brien & Huston, 1985) or objects that can be propelled in space (Benenson, Liroff, Pascal, & Cioppa, 1997). Preferences for such objects may exist because they afford greater opportunities for engaging in rough or active play In humans, these characteristics have in turn been suggested to relate to targeting or navigating abilities (for discussion, see Alexander, in press) that might be particularly useful for males for purposes of hunting or locating food or mates (Eals & Silverman, 1994; McBurney, Gaulin, Devineni, & Adams, 1997; Silverman & Eals, 1992). As suggested for females in regard to object that signal nurturance, males may therefore have evolved preferences for objects that invite movement.

Call me crazy, but it looks like their own explanations for their data actually undermine the conclusions they derived from it. According to them, the females weren't playing with the cooking pot and baby for any reason associated with the objects' human "femininity," but for reasons associated with species-specific gender roles (nurturing infant vervets with reddish faces). Furethermore, their explanations don't actually explain anything. They argue that males may enjoy moving things like cars and balls. But wait, the males also liked the pot and the stuffed dog. Is it easier to move stuffed dogs than baby dolls? I don't think so. And the females played with the brown dog as often as they played with the pink-faced baby doll. Why is that?

By the time I reached the end of the paper, I was forced to conclude that the authors' conclusions had absolutely nothing to do with their data whatsoever. While the female preference for "feminine" toys is obvious, the males don't seem to have a gender-preference at all. Furthermore, the female preference can't be explained by reference to any features of the objects themselves, and even if it could, it would be a result of feature preferences that are species-specific (e.g., the pink face of the baby and the red color of the pot), and thus wouldn't tell us anything about the origins of human gender-specific preferences. In short, the data tells us zilch, zero, nada, nothing. It's a terrible experiment, but in the hands of the press, with some overly-eager scientists who ran a silly experiment and then came to conclusions that had nothing to do with it giving the press quotes, this research becomes a profound revelation into the origins of human gender. Ugh.