Studies regarding childhood play behaviour with respect to toy choices, the sex of preferred play partners, and social play have shown that behavioural sex differences appear early in life (Hines, 2004, p. 17). By the first year, children prefer different toys, and these sex differences persist through childhood (Hines, 2004, p. 109). In general, boys tend to choose toys like cars, trucks, and guns, whereas girls prefer toys like dolls and tea sets (Berenbaum and Hines, 1992). For both boys and girls, about 80-90% of playmates are children of their own sex (Maccoby, 1988). Boys also spend more time than girls do in rough-and-tumble play, including play fighting and wrestling (Maccoby, 1988). However, the extent to which the behavioural sex differences differs among children, and we shall now examine the factors that account for such variations.
Scientists studying the processes that determine masculine and feminine development in various species have concluded that biological factors, particularly the gonadal hormones androgen and oestrogen, have powerful influences on the development of brain regions that show sex differences, and sex-typical behaviour (Hines, 2004, p. 2-3). A major consequence of being genetically male (XY sex chromosomes) or female (XX sex chromosomes) is differentiation of the gonads as testes versus ovaries. Differentiation of the gonads into testes versus ovaries results in markedly different hormone environments during development, and these differences direct most subsequent events in sexual differentiation, both permanently (organisational influences) and temporarily (activational influences) (Hines, 2004, p. 23-45).
For instance, congenital adrenal hyperplasia (CAH), a genetic disorder that results in the production of high androgen levels by the adrenal gland prenatally, is shown to affect sex-typical behaviour (Eagly et al., 2005, p. 13). Girls with CAH have partially masculinised genitalia and need to be treated with postnatal normalising hormones and surgery. They displayed more male-typical toy choices, and although they received more positive feedback for play with girls' toys than did unaffected girls, the encouragement appeared to be insufficient to override their interest in cross-sexed toys (Pasterski et al., 2005, p. 264). Similarly, high levels of testosterone during pregnancy related linearly to more masculine sex-type behaviour in preschool girls (Hines et al., 2002, p. 1678). These results suggest that prenatal biological factors, such as androgen and testosterone exposure, are powerful enough to limit postnatal social factors, such as the ability of parental responses to influence some aspects of sex-typed behaviour.
Despite the fact that biological factors can override social factors in...