A new commentary published in Evolutionary Psychological Science argues that sex differences in overhand throwing cannot be explained by socialisation alone, insisting that biological predispositions and experience work together across development. The authors, Robert O. Deaner and Michael P. Lombardo, frame their argument as an interactionist account rather than a simple nature-versus-nurture debate.
Researchers generally reject a binary choice between nature and nurture. Across disciplines including evolutionary biology, behavioural genetics and psychology, behaviour is treated as the product of ongoing interactions among genes, hormones, development, learning and the social environment. Yet explanations that attribute differences between women and men entirely to socialisation remain influential in some strands of gender research.
Deaner and Lombardo address this tension through the debate about the pronounced sex difference in overhand throwing. The gap is exceptionally large—roughly two standard deviations or more by adulthood—comparable in scale to the adult difference in height.
They respond to developmental biologist Anne Fausto-Sterling’s critique of their earlier suggestion that throwing ability partly reflects adaptations shaped by stronger ancestral selection on males.
Their central claim is that Fausto-Sterling’s account, which emphasises early social experience and ball-play opportunities, overlooks important evolutionary, anatomical, hormonal, cross-cultural and performance evidence. The authors argue that these factors work in concert rather than in competition.
An interactionist framework underpins their analysis: evolved predispositions and environmental influences are complementary in shaping throwing ability. They posit that ancestral males faced stronger selection for forceful and accurate overhand throwing, largely because they were more frequently involved in violent conflict and warfare.
Additional selection pressures are proposed, including hunting and confrontational scavenging, which may have reinforced throwing-related traits over many generations. The result, they suggest, could be anatomical, physiological and behavioural adaptations that support throwing performance.
Importantly, the authors emphasise that such 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. Differences in encouragement to play with balls and preexisting interests or capacities may influence activities children pursue and the responses they receive from caregivers, enabling socialisation to cultivate or amplify an evolved predisposition rather than create it from scratch.
The authors also challenge the claim that their evolutionary account rests on an outdated “Man the Hunter” narrative. They argue that their primary selection pressure lies in conflict between ancestral groups, notably warfare, with hunting serving a supplementary role. Anthropological data are cited as showing a substantial sexual division of hunting labour, with men generally hunting more often, pursuing larger animals and obtaining more meat—a pattern they say makes stronger selection for throwing among males plausible.
The evidence, they contend, extends beyond childhood throwing studies. They point to unusually large performance differences among adult throwers, differences in throwing accuracy and targeting, research linking prenatal androgen exposure with male-typical propulsive behaviour, and anatomical differences in the shoulder and arm that favour male throwing performance.
Across cultures, large differences persist even when both sexes face substantial throwing opportunities or when neither receives much practice; however, training can improve girls’ performance without consistently eliminating the gap, according to the authors.
They also argue that Fausto-Sterling’s observation of ten infants (five boys and five girls) cannot establish that maternal interaction caused differing engagement with balls, particularly because the study did not examine the mature, forceful overhand throw central to their hypothesis. More broadly, they contend that presenting developmental experience as an alternative to evolution misunderstands evolutionary theory: adaptations must emerge through developmental processes, and evidence that social experience contributes to a trait does not demonstrate that it fully accounts for it.
While acknowledging that some lines of evidence support their account—including targeting-related data—may derive from only one or a few studies, they concede that available quantitative hunting data may not represent all foraging societies.
In applying an interactionist framework to overhand throwing, the authors conclude that a complete explanation of behavioural sex differences must consider how biological predispositions and social experience jointly shape development. The paper is titled Sex Differences in Overhand Throwing are Completely Due to Socialization: A Blank Slate ‘Hypothesis’ Unconstrained by Evidence, and is authored by Robert O. Deaner and Michael P. Lombardo.
