In this post I’ll excerpt the portions of Lise Eliot’s Sci Am Mind article having to do with physical activity levels and aggression in boys and girls.
Boys are more physically active than girls, in infancy and throughout childhood. They kick, swing their arms and race around the house noticeably more than girls do, as many exhausted parents can testify. The difference may emerge before birth, although not every ultrasound study finds a sex difference in fetal movement. Nevertheless, the disparity is clear during the first year and expands through childhood, according to a 1986 analysis [possibly this?] of more than 100 studies by psychologist Warren Eaton and his colleagues at the University of Manitoba in Canada, which reveals that the average boy is more active than about 69 percent of girls.
That gap is statistically moderate, larger than differences in verbal and math skills but small enough to permit many exceptions to the rule, notably the 31 percent of girls who are more active than the average boy. Sex hormones — in particular, a relative abundance of testosterone in the womb — appear to trigger boys’ fidgetiness. And yet the sex difference in physical activity continues to widen during childhood, despite the fact that sex hormone levels do not differ between boys and girls from six months of age to puberty. Parenting is likely one factor amplifying the disparity. Mothers discourage physical risk taking more in daughters than in sons, suggest studies in the laboratory and on playgrounds. […] Peers also push conformity: in their preferred all-boy groups, energetic boys feed off one another, whereas energetic girls tend to settle down in clusters of more docile friends. In organized sports, girls start playing at a later age, quit earlier and join fewer teams overall than boys — differences that are influenced by parents and peers.
Here’s a Warren Eaton paper arguing that some but not all of the sex difference in motor activity results from girls maturing faster than boys.
Boys are more physically aggressive than girls, according to many studies, including a 2004 analysis [pdf] by psychologist John Archer of the University of Central Lancashire in England. That difference is linked to prenatal testosterone but not, surprisingly, to the resurgence in boys’ testosterone level in adolescence, because boys do not suddenly become more aggressive when they go through puberty, as Archer’s work also indicates. Nor is this sex difference absolute. Two- and three-year-old girls, for instance, frequently kick, bite and hit other people — not quite as much as toddler boys but about three times more than either sex does later in childhood. In addition, girls fight with indirect, or relational, aggression. Through gossip, ostracism, whispers and, most recently, harassing text messages, girls leave more scars on competitors’ psyches than on their bodies. […]
Thus, both sexes compete and both sexes fight; what differs is the degree to which such behavior is overt or hidden. Because physical aggression is a much greater taboo for girls than boys, they learn, even early in elementary school, to keep it below the surface, in the eye rolling and best-friend wars that teachers rarely notice and are harder to police.
Here’s a 1994 paper arguing it’s nonsensical to claim that males are more aggressive than females. Aggression is strategic. “Since females are physically weaker than males, they may early in life learn to avoid physical aggression, and instead develop other means [i.e., verbal]. Choice of aggressive strategy may become partly habitual, and also reinforced by social norms in the society in question.”
Next time: where do toy preferences come from?