By 9 weeks of age, dogs performed above chance expectation on a variety of tasks involving short-term memory, use of human social cues, and perceptual discriminations. Across development, individual difference in traits including spontaneous interest in humans, inhibitory control, and use of human communicative signals exhibited rank-order stability, suggesting consistent individual differences across time. Heritability analyses revealed that a substantial proportion of phenotypic variance was attributable to genetic factors, both in early ontogeny and young adulthood.