Chimpanzees and other great apes seem to be much less cooperative than humans overall, yet they nevertheless reliably help others in many instrumental circumstances. Although in many contexts the helping behavior of chimpanzees is quite similar to that of human children, recent studies using both behavioral and psychophysiological paradigms have revealed important differences, specifically, in the underlying motivations for prosocial behavior. Here, we provide both a synthesis of recent empirical work and an evolutionary hypothesis that can account for the differences in chimpanzee and human helping motivations.