This report presents data on 9-month-old twin pairs (n[MZ]=172; n[DZ]=333) from the Early Childhood Longitudinal Study, demonstrating that the role of genetic variation among infants is trivial and the shared and nonshared environment is substantial in accounting for the observed quality of infant-caregiver relationships. In contrast, maternal…

Measures of general cognitive ability in one- and two-year-old adopted and nonadopted infants and their parents were subjected to path analysis to estimate the contribution of genetic and environmental factors to short-term stability of mental ability. (Author/RH)

Examined infant verbal and nonverbal cognitive development for 1,937 pairs of same-sex 2-year-old twins. Found that verbal and nonverbal development correlated .42. Genetic factors were responsible for less than half of this phenotypic correlation. The genetic correlation between verbal and nonverbal abilities was only .30, suggesting that genetic…

Argues that an evolutionary account provides insight into developmental function and individual differences. Outlines some assumptions of evolutionary psychology related to development. Introduces the developmental systems approach, differential influence of natural selection at different points in ontogeny, and development of evolved…

Presents longitudinal data regarding detrimental effects through 36 months of age on intellectual, behavioral, and social-interactional development in a nonsupportive caregiving environment, and the continuing amelioration of those effects in a supportive caregiving environment. Suggests that mothers of fetally malnourished infants may have had…