Genetic research on general cognitive ability as a model for mild mental retardation

Surprisingly little is known about the generics of mild mental retardation, whereas much is known about the generics of general cognitive ability To the extent that mild mental retardation represents the low end of the distribution of the same genetic and environmental factors that affect variation in general cognitive ability throughout the distribution, genetic research on general cognitive ability can serve as a model to generate hypotheses to be tested in future genetic studies or? mild mental retardation. Five general findings from genetic research on general cognitive ability are discussed: (I) genetic influence increases during development; (2) genetic effects are broad (molar) rather than modular; (3) specific genes are beginning to be identified; (4) environment influences shared by family-members decline to negligible influence by adolescence; (5) associated measures of family environment are influenced by genetic factors.