Infants use physical size, but not prior possession, to predict conflict outcomes, and do not prefer prior possessors over contenders

Abstract

Ownership is a pervasive feature of human social life, yet its developmental origins remain unknown. One influential proposal is that human ownership psychology is built on an early-developing and evolutionary ancient sensitivity to first possession: Across species, conflicts over resources are often settled in favor of whoever held a resource first. Among humans, individuals who take what others already possess are often devalued as cooperative partners. Here, we focused on the inferences and preferences infants and toddlers form based on first possession. Across six laboratory experiments ( N = 227), we found positive Bayesian evidence that 10–18-month-old infants and young toddlers do not expect intruders will defer to first possessors in territorial conflict, and that 10–13-month-old infants do not prefer prior possessors over those who take (or attempt to take) possessions from others by force. In contrast, we found that infants do expect that larger, more physically formidable agents will prevail in territorial conflict, using identical methods. Hence, prior possession alone is not sufficient for shaping infants' expectations and evaluations in dyadic conflict, though physical formidability is.