Why sex differences in throwing cannot be explained by socialization alone

Sex differences in overhand throwing cannot be explained by socialization alone, according to a commentary published in Evolutionary Psychological Science that argues biological predispositions and experience work together across development.

Scientists generally reject a simple choice between nature and nurture. Research in evolutionary biology, behavioral genetics, and psychology instead treats behavior as the product of ongoing interactions among genes, hormones, development, learning, and the social environment. Nevertheless, explanations attributing differences between women and men entirely to socialization remain influential in some areas of sex and gender research.

Robert O. Deaner and Michael P. Lombardo examine this tension through a debate about the pronounced sex difference in overhand throwing. This difference is exceptionally large—reaching roughly two standard deviations or more by adulthood, a gap comparable in magnitude to the adult sex difference in height. Their commentary responds to developmental biologist Anne Fausto-Sterling’s critique of their earlier proposal that throwing ability partly reflects adaptations shaped by stronger ancestral selection on males.

Fausto-Sterling argues that differences in children’s early social experiences and opportunities for ball play can account for the development of the throwing gap. Deaner and Lombardo contend that this explanation overlooks relevant evolutionary, anatomical, hormonal, cross-cultural, and performance evidence.

The authors adopt an interactionist framework in which evolved predispositions and environmental influences are complementary rather than competing explanations. Their central hypothesis is that ancestral males experienced stronger selection for forceful and accurate overhand throwing, particularly because males were more frequently involved in violent conflict and warfare.

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Hunting and confrontational scavenging (stealing kills from other predators) may have provided additional selection pressures. Over many generations, these recurring demands could have favored anatomical, physiological, and behavioral traits that support throwing performance.

These evolved differences would not need to be fully formed at birth. Like walking or language, throwing develops through the interaction of biological capacities with experience, practice, and social input. Children may receive different levels of encouragement to play with balls, while preexisting differences in interests or physical capacities may also influence the activities they seek out and the responses they receive from caregivers. Socialization can therefore cultivate or amplify an evolved predisposition without having created it entirely.

The authors first dispute the claim that their evolutionary account depends principally on the traditional image of “Man the Hunter.” They say their primary proposed selection pressure is conflict between ancestral groups, especially warfare, with hunting serving as a complementary influence. They also argue that the anthropological evidence continues to show a substantial sexual division of hunting labor. Although women hunt in some societies, quantitative data indicate that men generally hunt more often, pursue larger animals, and obtain considerably more meat. In the authors’ view, such patterns make it plausible that males faced stronger selection for throwing-related abilities.

The authors next argue that the evidence extends well beyond childhood throwing studies. They point to an unusually large performance difference between male and female javelin throwers; differences in throwing accuracy and targeting; research connecting prenatal androgen exposure (levels of male sex hormones experienced in the womb) with male-typical propulsive behavior; and anatomical differences in the shoulder and arm that generally favor male throwing performance.

Large differences have also been observed among children in societies where both sexes receive substantial throwing opportunities or where neither receives much practice, while training improves girls’ performance without consistently eliminating the gap.

Finally, Deaner and Lombardo maintain that Fausto-Sterling’s observations of ten infants (five boys and five girls) cannot establish that maternal interaction caused the children’s differing engagement with balls, particularly because the study did not examine the mature, forceful overhand throw addressed by their hypothesis. More broadly, they argue that presenting developmental experience as an alternative to evolution misunderstand evolutionary theory: adaptations must emerge through developmental processes, and evidence that social experience contributes to a trait does not demonstrate that experience fully accounts for it.

The authors acknowledge that some lines of evidence supporting their account, including evidence concerning targeting, come from only one or a few studies. They also note that available quantitative hunting data may not represent all foraging societies.

By applying an interactionist framework to overhand throwing, the commentary argues that a complete explanation of behavioral sex differences must examine how biological predispositions and social experience jointly shape development.

The paper, “Sex Differences in Overhand Throwing are Completely Due to Socialization: A Blank Slate ‘Hypothesis’ Unconstrained by Evidence,” was authored by Robert O. Deaner and Michael P. Lombardo.