A classification of natal influences is proposed with a model of their operation. Natal influences affect maternal capacity, maternal load, and maternal efficiency. Since maternal load is increased in twin pregnancy, results of twin studies must be generalized with caution. The method of co-twin control is exemplified by examination of a small…

This paper repudiates Jensen's hypothesis that differences in IQ scores and scholastic achievement in Negro and white children are genetically based. Specifically, Jensen's identification of IQ scores as a measure of abstract reasoning and problem solving and of levels of ability, and his evaluation of the magnitude of the genetic component in IQ…

Much of our thinking about contemporary social problems reflects tacit presuppositions regarding the operation of heredity and environment in human behavior. These beliefs have important implications for practical decisions. Advances in genetics, psychology, anthropology, and other disciplines have contributed much to a clarification of the…