Human beings have remarkable skills of self-control, but the evolutionary origins of these skills are unknown. This study investigates the evolutionary bases, as well as the developmental changes, of humans?reactivity and self-regulatory skills. Human children at 3 and 6 years of age were systematically compared with one of humans' two nearest relatives, chimpanzees, on a battery of six tasks. Three-year-old children and chimpanzees were very similar in their abilities to resist an impulse for immediate gratification (when that led to greater rewards later), repeat a previously successful action (when the situation had changed), attend to a distracting noise (when concentrating on a problem), and quit in the face of repeated failure. Six-year-old children were more skillful than either three-year-olds or chimpanzees at controlling their impulses. These results suggest that humans' most fundamental skills of self-control - as part of the overall decision-making process - are a part of their general great ape heritage, and that their species-unique skills of self-control begin at around the age at which many children begin formal schooling.