Hassett et al. (2008)

• Sex differences in rhesus monkey toy preferences

  Parallels those of children
• Socialization processes, parents, or peers encouraging play with gender specific toys are thought to be the primary force shaping sex differences in toy preference
• A contrast in view is that toy preferences reflect biologically determined preferences for specific activities facilitated by specific toys
• Sex differences in juvenile activities, such as rough and tumble play, peer preferences, and infant interest, share similarities in humans and monkeys
• We compared the interactions of 34 rhesus monkeys, living within a 135 monkey troop, with human wheeled toys and plush toys
• Male monkeys, like boys


  • Showed consistent and strong preferences for wheeled toys
• Female monkeys, like girls


  • Showed greater variability in preferences
• The magnitude of preference for wheeled over plush toys


  Differed significantly between males and females
• The similarities to human findings demonstrate that such preferences can develop without explicit gendered socialization
• Rational


  (in classical economic theory) economic agents are able to consider the outcome of their choices and recognise the net benefits of each one
• Consumers act rationally by


  Maximising their utility
• Producers act rationally by


  Selling goods/services in a way that maximises their profits
• Workers act rationally by


  Balancing welfare at work with consideration of both pay and benefits
• Governments act rationally by


  Placing the interests of the people they serve first in order to maximise their welfare
• Rationality in classical economic theory is a flawed assumption as people usually don't act rationally
• Marginal utility


  The additional utility (satisfaction) gained from the consumption of an additional product
• If you add up marginal utility for each unit you get total utility
• at the lack of a male vervet preference for masculine toys implied that boys' strong preferences for masculine toys reflected stronger gendered socialization of boys' toy preference relative to girls' toy preference (Alexander and Hines, 2002)
• This explanation seems unlikely as it would imply that their finding of greater female vervet preference for feminine toys means that vervet monkey females are strongly socialized to prefer female toys, whereas girls' toy preferences are not socialized
• A more parsimonious explanation is that since the vervets were never presented with actual toy choices the results do not accurately reflect preferences, but show substantial cross sex willingness to play with any toy
• Thus although there are substantial concordances between human and nonhuman primate gendered social behavior, nonhuman primate data leave unresolved the relative concordance between human and nonhuman primate gendered toy preferences
• We investigated toy preferences in rhesus monkeys living in a 135 member long-term stable outdoor group by presenting the group with multiple trials of simultaneous access to different two toy combinations of multiple toys: one putatively masculine and one putatively feminine
• We present here striking evidence of a sex difference in rhesus monkey preference for human gender-stereotyped toys paralleling that reported in humans, suggesting that gender differences in toy choice may reflect evolved sex differences in activity preferences not primarily resulting from socialization processes
• Subjects were rhesus monkey (Macaca mulatta) members of a multi-male, multi-female social group of 135 animals that had lived together for more than 25 years at the Yerkes National Primate Research Center Field Station
• This social group had a species-typical multiple matriline social structure with a full age-range of group members from infants to adults
• Fourteen animals were not included in analyses because they had been exposed to varying hormonal treatments prenatally, but there were not enough subjects in any one treatment group to systematically analyze preferences
• Additionally, the interactions of 39 newborn (0–3 months) infants, while minimal, were not coded due to difficulty in consistent individual identification
• This left 61 females and 21 males as potential subjects
• Subjects were housed with their natal group in 25m × 25m outdoor compounds with attached temperature-controlled indoor quarters
• Water was continuously available, and the animals were fed monkey chow twice daily, supplemented once per day with fruits and vegetables
• Because we hypothesized that some aspects of sexually differentiated toy preferences reflect activity preferences, we categorized our toys not by traditional gender assignment, but by specific object properties that made our categories comparable, though not exact matches, to stereotypical gender assignments
• Plush toys


  • Winnie-the-Pooh™
  • Raggedy-Ann™
  • a koala bear hand puppet
  • an armadillo
  • a teddy bear
  • Scooby-Doo™
  • a turtle
• Wheeled toys


  • a wagon
  • a truck
  • a car
  • a construction vehicle
  • a shopping cart
  • a dump truck
• Seven 25min trials were conducted within the large indoor/outdoor enclosure that housed the social group
• Prior to each trial, subjects and other social group members were sequestered indoors while one wheeled and one plush toy separated by 10m were placed in the outdoor living area, with left or right placement location counterbalanced across trials
• Monkeys were then released into the outdoor area and each toy and any animal interacting with it was videotaped using separate cameras for each toy
• In one case, a plush toy was torn into multiple pieces, ending the trial 7min early
• After each trial, toys were removed from the outdoor area
• The identity of every animal interacting with the toys and specific behaviors (Table 2) directed towards the toys were coded from the videotapes by two observers working together to achieve consensus on both identity and behaviors
• Rank had been assessed for all individuals in the group through extensive behavioral observations documenting the directionality of grooming, dominance, and submission behavior