Letter to the Editor

Monkeys, girls, boys and toys: A confirmation: Letter regarding “Sex differences in toy preferences: Striking parallels between monkeys and humans”

This review will focus on some of the literature that pertains to the psychological effects of sex differentiation. The topics covered will include, toy play preferences, cognitive differences and the effects of sex differentiation on measures of sexual orientation. The majority of the key findings will come from studies that have focused on individuals with the disorder of sex development (DSD), congenital adrenal hyperplasia (CAH).

The chapter reviews the growth and development of the marmoset, rhesus macaque, and cynomolgus monkey with an emphasis on hormonal regulation of the female reproductive cycle and growth of the conceptus through sexual maturity. Comparative aspects of genetics and cardiovascular, respiratory, and renal physiology, with a brief discussion on development of the brain and the comparative aspects of the visual system, are included. Tables describe comparative genome statistics and chromosomal homology, developmental milestones, vertebral and dental anatomy, common cardiovascular, renal, and respiratory physiological parameters, and electrocardiographic parameters. Discussion is limited to these three nonhuman primate species of greatest toxicological interest.

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.

Despite claims in the popular press, experiments investigating whether female are more efficient than male observers at processing expression of emotions produced inconsistent findings. In the present study, participants were asked to categorize fear and disgust expressions displayed auditorily, visually, or audio-visually. Results revealed an advantage of women in all the conditions of stimulus presentation. We also observed more nonlinear probabilistic summation in the bimodal conditions in female than male observers, indicating greater neural integration of different sensory-emotional informations. These findings indicate robust differences between genders in the multisensory perception of emotion expression.