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[Show abstract][Hide abstract] ABSTRACT: The theoretical debate over the relative contributions of nature and nurture to the sexual differentiation of behaviour has increasingly moved towards an interactionist explanation that requires both influences. In practice, however, nature and nurture have often been seen as separable, influencing human clinical sex assignment decisions, sometimes with disastrous consequences. Decisions about the sex assignment of children born with intersex conditions have been based almost exclusively on the appearance of the genitals and how other's reactions to the gender role of the assigned sex affect individual gender socialisation. Effects of the social environment and gender expectations in human cultures are ubiquitous, overshadowing the potential underlying biological contributions in favour of the more observable social influences. Recent work in nonhuman primates showing behavioural sex differences paralleling human sex differences, including toy preferences, suggests that less easily observed biological factors also influence behavioural sexual differentiation in both monkeys and humans. We review research, including Robert W. Goy's pioneering work with rhesus monkeys, which manipulated prenatal hormones at different gestation times and demonstrated that genital anatomy and specific behaviours are independently sexually differentiated. Such studies demonstrate that, for a variety of behaviours, including juvenile mounting and rough play, individuals can have the genitals of one sex but show the behaviour more typical of the other sex. We describe another case, infant distress vocalisations, where maternal responsiveness is best accounted for by the mother's response to the genital appearance of her offspring. Taken together, these studies demonstrate that sexual differentiation arises from complex interactions where anatomical and behavioural biases, produced by hormonal and other biological processes, are shaped by social experience into the behavioural sex differences that distinguish males and females.
Journal of Neuroendocrinology 02/2009; 21(4):421-6. DOI:10.1111/j.1365-2826.2009.01832.x · 3.14 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Girls and boys differ in their preferences for toys such as dolls and trucks. These sex differences are present in infants, are seen in non-human primates, and relate, in part, to prenatal androgen exposure. This evidence of inborn influences on sex-typed toy preferences has led to suggestions that object features, such as the color or the shape of toys, may be of intrinsically different interest to males and females. We used a preferential looking task to examine preferences for different toys, colors, and shapes in 120 infants, ages 12, 18, or 24 months. Girls looked at dolls significantly more than boys did and boys looked at cars significantly more than girls did, irrespective of color, particularly when brightness was controlled. These outcomes did not vary with age. There were no significant sex differences in infants' preferences for different colors or shapes. Instead, both girls and boys preferred reddish colors over blue and rounded over angular shapes. These findings augment prior evidence of sex-typed toy preferences in infants, but suggest that color and shape do not determine these sex differences. In fact, the direction of influence could be the opposite. Girls may learn to prefer pink, for instance, because the toys that they enjoy playing with are often colored pink. Regarding within sex differences, as opposed to differences between boys and girls, both boys and girls preferred dolls to cars at age 12-months. The preference of young boys for dolls over cars suggests that older boys' avoidance of dolls may be acquired. Similarly, the sex similarities in infants' preferences for colors and shapes suggest that any subsequent sex differences in these preferences may arise from socialization or cognitive gender development rather than inborn factors.
Archives of Sexual Behavior 03/2010; 39(6):1261-73. DOI:10.1007/s10508-010-9618-z · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: During the intrauterine period a testosterone surge masculinizes the fetal brain, whereas the absence of such a surge results in a feminine brain. As sexual differentiation of the brain takes place at a much later stage in development than sexual differentiation of the genitals, these two processes can be influenced independently of each other. Sex differences in cognition, gender identity (an individual's perception of their own sexual identity), sexual orientation (heterosexuality, homosexuality or bisexuality), and the risks of developing neuropsychiatric disorders are programmed into our brain during early development. There is no evidence that one's postnatal social environment plays a crucial role in gender identity or sexual orientation. We discuss the relationships between structural and functional sex differences of various brain areas and the way they change along with any changes in the supply of sex hormones on the one hand and sex differences in behavior in health and disease on the other.
Frontiers in Neuroendocrinology 02/2011; 32(2):214-26. DOI:10.1016/j.yfrne.2011.02.007 · 7.04 Impact Factor