The prenatal hormones affect the sexually dimorphic pathways in the brain during the early months of fetal development, altering the threshold for behavior traits defined as boyish or girlish. The prenatal program does not preordain psychosexual differentiation as masculine or feminine but instead establishes a predisposition for behavior traits that are gender-shared but threshold-dimorphic.
The readiness with which some behavior traits are evoked in males is associated with boyishness and built into a masculine gender-identity; the same principle applies to girlishness and a feminine gender-identity.
Sex of assignment and sex of rearing exert their respective influences upon an organism which already contains behavioral predispositions deriving from the prenatal program. Presumably, gender-dimorphic behavior traits affect the responses of parents and other caretakers, confirming sex of assignment and the program of upbringing. Similarly, sex of assignment is likely to evoke differential parenting responses which exert a feedback effect on the infant. For example, mothers are reported to vocalize to and smile more frequently at female infants and to employ nonverbal arousal stimuli more frequently with boys. Boys also are fed more often, held upright more frequently and discouraged from touching. The interaction of differential parental expectations and of the daily practices of rearing in relation to psychosexual differentiation and infant behavior is only beginning to be investigated and the findings to date are tentative.
In the first weeks and months of life, when infant behavior is characteristically variable, efforts to discover gender differences are extraordinarily difficult. Moreover, differences attributed to gender may stem from social and cultural practices which are overlooked unless cross-cultural comparisons are made. One recent investigation showed that the early gender differences reported in American studies were not replicated in European studies, possibly because of variations in circumcision practice on the two continents. An intrusive physical procedure, circumcision, affected the male infant’s behavior by increasing irritability which, in turn, affected parenting practices. In the neonate and infant, variations in state of arousal, in temperament, and in sensorimotor capacities may have a more pervasive effect on socioemotional behavior than gender status or parenting practices do. The possibility is not surprising since interaction with the behavior environment appears to be essential to the differentiation of gender-dimorphic behavior. The effect of learning, from stimulus and response, from reward and punishment or neglect, and from observation and copying, is a cumulative phenomenon, visible only after the passage of time.
In the first two years of life sexuality is expressed mainly in the sensuous attachment of the child to the parents and is common to both boys and girls. Sociosexual differentiation as male or female is initiated in the discovery and exploration of one’s own body and in the gender-dimorphic patterns of rearing. These events are precursors of the sexually erotic partnerships which will emerge in adolescence and adulthood.
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