Young children's friendship expectations align with evolutionary frameworks

Across the lifespan, friends are critical social partners. Prominent evolutionary theories—such as the Banker's Paradox (Tooby & Cosmides, 1996)—propose that friendships are based not on people's traits and dispositions, but rather on selective provisioning of support and partiality. Broadly, people expect friends to provide help in times of need, and expect support to be directed most towards one's closest affiliates (see also the Alliance Hypothesis, DeScioli & Kurzban, 2009). The present article integrates research from developmental psychology and cognitive science to point to converging expectations in early childhood: By 5 to 6 years of age, children expect friendship to be a ranking-based relationship wherein friends are socially obligated towards each other. We cover research demonstrating children's understanding of friendship, including which behaviors they see as diagnostic of friendship, how they weigh different cues of (potential) friendship, which social obligations they expect friends to adhere to, and how these expectations influence their navigation of the social world. We end by discussing future avenues of research, including specification of rankings, friendship jealousy, forgiveness, and origins of friendship cognition in infancy.