hassett (monke)

Authors: Janice M. Hassett, Erin R. Siebert, Kim Wallen
Affiliations:
- Emory University Department of Psychology and Yerkes National Primate Research Center, Atlanta, GA 30322
- Summer Undergraduate Research Experience Program, Emory University
Key Focus: Investigation of sex differences in toy preferences between rhesus monkeys and children.
Main Hypothesis: Toy preferences reflect biologically determined activity preferences, rather than solely socialization.
Keywords: sex differences, toy preference, gender, hormones, rhesus monkey, children, socialization

Toy play is a robust behavioral sex difference with moderate to very large effect sizes (Cohen-Bendahan et al., 2005; Collaer and Hines, 1995).
Boys show stronger preferences for masculine-type toys compared to girls who do not show a statistically significant preference for one type over another (Berenbaum and Hines, 1992).
Gender socialization theory: Societal endorsement drives conformity to expected gender roles (Martin and Little, 1990).
Girls may have flexibility in gender-typed behavior, contrasted with boys who exhibit stronger preferences for gender-specific activities (Bussey and Perry, 1982).

Parallels to Activities: Differences in toy preferences may stem from inherent preferences for specific activities (Miller, 1987).
Prenatal Hormonal Influence: Differences within biological sex preferences arise from exposure to hormones influencing behavior, as evidenced in girls with congenital adrenal hyperplasia (CAH), who show increased boy-typical toy preference (Berenbaum and Hines, 1992; Meyer-Bahlburg et al., 2004).

Sample Size: 34 rhesus monkeys from a 135-member troop living at the Yerkes National Primate Research Center Field Station.
Demographics: 21 males, 61 females (aged from infants to adults). Excluded individuals due to hormonal treatment or inability to code interactions.
Monkeys housed in species-specific outdoor enclosures, with continual access to water.

Toy Categories: Toys categorized based on object properties, not traditional gender assignments:
- Wheeled Toys: Comparable to masculine vehicle toys (e.g., truck, car, wagon).
- Plush Toys: Comparable to feminine dolls (e.g., teddy bear, Scooby-Doo™).
Toys designed to reflect features facilitating specific activities.

Experimental Design: Conducted seven 25-minute trials where one wheeled and one plush toy were presented simultaneously to monkeys.
Behaviors coded from videotapes focusing on interactions with each toy, involving extensive observational protocols to ensure accuracy.

Frequency of Interactions:
- Male monkeys showed a significant preference for wheeled over plush toys.
- Total Frequencies: Males: 9.77, Females: 6.96.
- Significant difference: Z = -2.09, p = .04.
- Female monkeys did not show reliable preference, engaging comparably with both toy types.

Total Duration showed similar patterns for preferences with males interacting longer with wheeled toys compared to plush toys.
Females showed no significant duration preference either toy type.

Cohen’s d: Used to measure effect size, suggesting a moderate to strong difference between males and females in toy preference behaviors.
Nonparametric tests used to analyze duration due to non-normal distribution.

Male rhesus monkeys mirrored the strong gender-specific toy preference exhibited in human boys, preferring wheeled toys.
Female rhesus monkeys exhibited a more flexible interaction pattern, akin to human girls, with no significant preference.
Suggestion that sex differences in toy preferences are not purely influenced by socialization but are also biologically driven by hormonal influences on behavior.

Toy preferences reflect deeper activity preferences influenced by hormonal backgrounds rather than solely socialized norms.
Complexity of social structure among rhesus monkeys indicates that adult socialization is not the primary factor determining sex differences in toy interaction behavior.

Contributions from Jessica Raper and Anne Graff in data collection and development.
Funding support from Howard Hughes Medical Institute and various NIH grants.

A comprehensive list of studies and findings relevant to sex differences in play behavior in children and nonhuman primates, providing foundational support to the hypotheses discussed.

Figure 1: Illustrations demonstrating sex differences in play with stereotypically masculine and feminine toys.
Table 1: Overview of monkey demographics sorted by sex and rank.
Table 2: Descriptions of coded behaviors for interactions with toys.
Table 3: Summary of mean frequencies and durations of interactions with plush and wheeled toys by sex.