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Analyses using data from adoption and twin longitudinal studies tell an interesting story of the diversity of processes controlling the development of general cognitive ability from infancy through middle childhood. The nonshared environment, uniquely experienced by individuals, clearly does not drive the developmental process. Its influences are transitory and occasion-specific. The environmental influences shared by siblings and twins were found to be of a global nature which could be the result of such monolithic factors as socioeconomic status and other relatively constant influences on the family. These influences appear not to drive the developmental process. It appears that genes are driving the developmental process. New genetic variation appears at each age, and that variation persists onto later ages. This is characteristic of a truly developmental process. The amount of variation appears to be decreasing through age 4, but rises substantially at age 7, after the child has completed the first year of schooling.