Results

Childrens' toy selections (wheeled toys vs. plush toys) reflect hormonally influenced behavioral and cognitive biases without explicit gendered socialization

Children explain personal toy preferences in terms of what can be done with it (55%) rather than gender-appropriateness of the toy (<1%)

Juvenile male rhesus monkeys engage in more rough-and-tumble play, juvenile female monkeys show a greater interest in young infants

Male vervet monkeys play longer with "male" toys (car and ball) than "female" toys (doll and pot); vice versa with female monkeys; no gender differences in preference for "neutral" toys (picture book and stuffed dog)

Infant boys show a looking preference for mechanical motion over biological motion, while infant girls show the opposite pattern

Girls with CAH (a prenatal hormonal anomaly) strongly prefer male-typical toy play despite parental encouragement of female-typical toy play (i.e. - nature > nurture)

Gender norms and identites are not purely social constructs

Men and women only have 10-24% overlap of personality characteristics

Women have more empathy and higher altruistic values; men have more altruistic love (i.e. - sacrifice/selflessness)

Male baby chimpanzees have significantly more adult male social partners than baby female chimpanzees; there is no difference between the genders in adult female social partners

Young female chimpanzees use sticks to facilitate play-mothering, which lasts until motherhood; young male chimpanzees do not exhibit such behavior

Women cry 2-10 times more frequently than men (2.5-5.0 times/month vs. 0.5-1.5 times/month)

Gender differences in crying proneness are larger in wealthier, more democratic, and feminine countries (i.e. - freer & less "patriarchal" countries)

Testosterone injections in various species of animal lowers incidence of crying

There is a large effect size (d=0.93) on the Things-People dimension, with men prefering to work with things and women prefering to work with people

Sex differences in most psychological (and in many physical) traits are larger in cultures with more egalitarian sex role socialization and greater sociopolitical gender equity

Men and women deal with stress differently ("fight or flight" vs. "tend and befriend")

Among FtM transsexuals on hormone therapy, grey matter associated with language centers markedly decreased (while white matter connecting the areas increased to compensate)

Structural connectomes of transsexuals change in opposite paths following hormone therapy

Significant sex differences in toy preferences are found in infants and toddlers (ages 9 months to 32 months), without parents being present in the room for gendered reinforcement.