Twin Studies

As the most widely used research design for exploring genetic and environmental influences [Page 2273]on traits or behaviors, twin studies help us understand the factors that contribute to individual differences within a population. Although one’s genotype is established at fertilization, questions about the relative importance of genes and environments on behavior are relevant throughout the life span because both genes and environments are dynamic in nature and their influences on traits or behaviors may change across age. Moreover, the fact that a trait is heritable does not mean that the same genetic influences operate at each age. That is, the genes that influence a trait in infancy may differ from those that influence the trait in later developmental periods. This is also true of environments. ...