Toy story: Why do monkey and human males prefer trucks?: Comment on “Sex differences in rhesus monkey toy preferences parallel those of children” by Hassett, Siebert and Wallen

Abstract

Parents of young children will tell you that boys like different toys than girls; they are intrigued by Bob the Builder, Transformers of all kinds, trucks, police cars, front loaders, bikes, skate boards, and wagons. Girls too like bikes, cars and Legos, but also play with stuffed animals and dolls, toys that boys find less appealing for active play. Is this difference in toy preference due exclusively to socialization by parents, other children, and the media, or are there basic perception/action differences between males and females that make some toys a better “fit” for or more attractive to one sex than another? In this issue, Hassett et al. (2008) provide evidence that male and female rhesus monkeys (Macaca mulatta) of all ages and ranks show preferences for wheeled and plush toys that resemble the preferences shown by human children in many studies of toy choice. This cross-species demonstration of male–female differences in toy choice strongly supports and extends prior work with humans (e.g., Berenbaum and Hines, 1992; Campbell et al., 2000; Pasterski et al., 2005; Serbin et al., 2001) and vervet monkeys (Alexander and Hines, 2002) showing that sexually dimorphic toy preferences reflect basic neurobiological differences between males and females and are not caused solely by socialization, as has been suggested by cognitive-social theories of gender role behavior (Caldera et al., 1989; Carter and Levy, 1988; Pomerleau et al., 1990; Roopnarine, 1986). Despite repeated demonstrations of sex differences in toy choice that are difficult to explain by socialization alone (e.g. Alexander, 2003; Nordenstrom et al., 2002; Meyer-Balhberg et al., 2004; Pasterski et al., 2005; Serbin et al., 2001), there has been considerable resistance to the idea that toy choice/preference is influenced by genetics and hormones, in part, because the wheeled and mechanical toys that males prefer are not part of our evolutionary history. How could male brains evolve to prefer objects that did not even exist when our modern Homo sapiens brain was shaped by adaptive forces? What is it about toys that make them “male” or “female”? Toy preference is a complex cognitive process determined by sensory, perceptual and motor processes; what sexually dimorphic neural mechanisms control these differences? The findings of Hassett and colleagues have important implications for all of these issues.