Supplementary material from "Young Children Exhibit Sex-Biased Strategies to Obtain Resources "

Mammalian males’ strategies for obtaining resources have been well-established and typically depend on direct contests that produce hierarchies. Although less well-documented, current evidence suggests that in female philopatric communities, females engage in contests often with coalition partners who are typically female kin. When kin are not present however, females of similar age appear more egalitarian and tend to avoid contests. To examine whether phylogenetically similar sex-biased strategies to obtain valuable resources occur in humans, we held a contest for 50 pairs of unrelated, familiar 3-7-year-old children from diverse backgrounds. We show that the majority of female pairs spontaneously approached the resources side-by-side then briefly competed to obtain the resources. In marked contrast, in over half of the male pairs one male deferred to his partner who then gained unimpeded access to the most valuable resource. Sex-differentiated strategies however appeared only with same-sex peers. Results show that already by early childhood, humans exhibit sex-biased strategies to regulate competition between same-sex peers. Sex-segregated peer groups however mean that by adulthood, each sex has practiced strikingly different strategies for obtaining resources from same-sex peers.