Brief articleMale more than female infants imitate propulsive motion
Highlights
► Male more than female infants imitate propulsive motion. ► Males preferentially imitate a male over a female model. ► No initial sex differences in propulsive motions occur in infancy.
Introduction
How humans develop sex-typed activity preferences and interests generates much controversy. Cross-culturally, sex differences in activities and interests emerge around 18 months (Gosso et al., 2005, Huston, 1986, Ruble et al., 2006) and continue throughout life (Wood & Eagly, 2002). Beginning in the second year, boys exhibit greater interest than girls in transportation vehicles, weapons, tools, and rough-and-tumble play, whereas girls prefer dolls and objects associated with domestic activities (Huston, 1986, Ruble et al., 2006).
Two predominant socialization explanations exist for early sex-typed activity preferences. According to the first, children learn to categorize themselves as male or female, then preferentially imitate same-sex adult and peer models. Between 17 and 21 months, when gender self-labeling begins to emerge, use of gender labels is associated for boys with play with a truck over a doll and for girls with the reverse (Zosuls et al., 2009). Even before boys could label themselves by gender however, they preferred trucks more than girls did (Zosuls et al., 2009). This suggests that another earlier mechanism likely exists.
A second socialization explanation rests on reinforcement. In a meta-analysis of sex-typed parental treatment of children, parents encouraged sex-typed activities and household chores (Lytton & Romney, 1991). Thus, parents may reward boys more than girls for playing with trucks. Reinforcement however may build upon innate predispositions (Scarr and McCartney, 1983, Öhman and Mineka, 2003).
Two sources support the role of innate predispositions. First, beginning in early childhood, prenatally androgenized girls with congenital adrenal hyperplasia (CAH) more than controls play with vehicles, weapons, and tools (Berenbaum and Hines, 1992, Berenbaum and Snyder, 1995, Pasterski et al., 2005).
Second, non-human primates exhibit sex differences in toy preferences that resemble those of humans. Free-roaming male more than female chimpanzees, Pan troglodytes, use sticks for hitting, whereas females as juveniles are more likely to carry sticks as if they were babies (Kahlenberg & Wrangham, 2010). Further, male vervet monkeys, Cercopithecus aethiops sabaeus, play longer than females with a toy car and ball, whereas females play longer with a doll and pot (Alexander & Hines, 2002). Likewise, male more than female rhesus monkeys, Macaca mulatta, play longer with wheeled vehicles (Hassett, Siebert, & Wallen, 2008).
Innate predispositions for perceptual attributes or motor affordances of objects therefore likely provide a foundation for sex-typed activity preferences. Investigating perceptual attributes, researchers presented neonates with a live adult female face and a mobile, one at a time for 70 s. Female neonates looked more at the face than the mobile, whereas male infants exhibited the reverse pattern (Connellan, Baron-Cohen, Wheelwright, Batki, & Ahluwalia, 2000). Likewise, infants 5 months of age viewed a toy truck and a doll side-by-side in two 10-s blocks. No sex difference in looking time emerged, but girls fixated more times on the doll than the truck, while boys did not discriminate (Alexander, Wilcox, & Woods, 2009). Other studies however find early sex-differentiated perceptual preferences only for boys at 9 months (Campbell, Shirley, Heywood, & Crook, 2000) or not at all (e.g., Serbin, Poulin-Dubois, Colburne, Sen, & Eichstedt, 2001).
Motor affordances provide a theoretically appealing foundation for sex-typed activity preferences. Males throw more forcefully than females beginning early in childhood (Thomas & French, 1985). Further, most mammalian male (but not female) sexual and aggressive behaviors require executing a forward thrusting motion. Similarly, young boys’ sex-typed activities involving weapons, vehicles, and tools often require a propulsive motion. In support of the hypothesis that propulsion underlies male sex-typed preferences, 3–4-year-old boys who punched a puppet more forcefully were rated by teachers as engaging in more male sex-typed activities and chose more toys that required propulsive movement (Benenson, Liroff, Pascal, & Della Cioppa, 1997).
Further, Bandura’s experiments on imitation suggest that children are primed to learn some movements more rapidly than others, and that one component of physical aggression, propulsive movements, may appeal more to males. Specifically, 90% of 4–5-year-old children imitated knocking down a doll, but only 45% imitated marching across a room (Bandura & Huston, 1961). Moreover, when 3–5-year-old children viewed a male and female model physically and verbally aggressing against a punching bag doll, boys imitated the physically aggressive movements more than girls, particularly of the male model (Bandura, Ross, & Ross, 1961). Further, even without a model, boys exhibited more propulsive movements than girls, such as hitting, punching, and gun play. The predominant interpretation has been that boys imitated the male model’s aggression because they understood conceptually that they are male and males behave aggressively (Bandura and Bussey, 1999, Kohlberg, 1966, Martin et al., 2002, Zosuls et al., 2009). An alternative, but not mutually exclusive interpretation however, is that boys find males’ propulsive movements more appealing than females’ movements.
Here we test whether boys more than girls will imitate a simple non-aggressive propulsive movement of a male model, before gender self-labeling and understanding of maleness and aggression occur. Consequently, we chose 6–9-month-old infants as participants. To control for perceptual preferences, only one object, a balloon, was employed.
Section snippets
Procedure
Twenty-five male (M = 6.80 months, SD = 1.22) and 20 female (M = 7.21 months, SD = 1.36) infants participated while waiting for their well-baby visits at a health clinic. One-third of the 45 infants were Caucasian, 1/3 Hispanic, and the remainder came from Black, Asian, and mixed-race backgrounds with similar distributions within sex.
Participating infants were brought to a conference room which contained a large, opaque tent containing the experimental apparatus (see Fig. 1). The parent sat on a chair
Results
A preliminary repeated measures analysis of variance (ANOVA) on infants’ absolute looking times to the female versus male models with infants’ sex as the independent variable showed no sex differences occurred in looking time, F(1, 43) = 0.89, n.s. Consistent with a prior finding that 3- to 4-month old infants look more at female adults (Quinn, Yahr, Kuhn, Slater, & Pascalis, 2002), infants of both sexes looked slightly more at the female model (males: M = 77.20s, SD = 2.80; females: M = 80.92s, SE =
Discussion
Male infants imitated propulsive motion more than female infants did. The extent of this effect correlated positively with the proportion of time spent viewing the male model hitting a balloon. Three interpretations arise.
First, male infants may consciously label themselves and the adults by gender then selectively imitate the motions of the male adult that are associated with male behavior (Zosuls et al., 2009). Although infants do learn implicitly to categorize adults by gender as early as 3
Conclusions
The current research demonstrates that male more than female infants imitate propulsive movements of a male adult model. Further research must examine sex-differentiated preferences early in infancy and the extent to which they guide future sex-typed activities and interests.
Acknowledgements
We thank David Osler and the staff of the Cambridge Health Alliance for their invaluable assistance, as well as the Goelet Fund, the Mary Gordon Roberts Fellowship, Harvard College Research Program, and Dean’s Summer Research Award for support. We also thank Anastasyia Yakhkind for help with data collection; Matthew Garcia, Ashley Jovanovski, Timothy Kim, Jennifer McKee, Amy Tao, and Beau Tremitiere, for assistance with coding; and Henry Markovits for technical assistance.
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