Behavioral genetics is a field of research that investigates the relative effects of heredity and environment on behavior and ability (Plomin, 1997). Two of the primary methods used by behavioral geneticists are the twin study method, first used by Galton (1975) in his studies of heredity, and the adoption method. In the twin study method, researchers studies identical twins (monozygotic twins) and fraternal twins (dizygotic twins) to determine how much they resemble each other on a variety of characteristics. Identical twins have exactly the same genes because a single sperm cell of the father fertilizers a single egg of the mother, forming a cell that then splits and forms two human beings-“carbon copies.” But fraternal twins are no more alike genetically than any two siblings born in the same parents. In the case of fraternal twins, two separate sperm cells fertilize two separate eggs that happen to be released at the same time during ovulation. Twins, who are raised together, whether identical or fraternal, have similar environments. If identical twins raised together are found to be more alike than fraternal twins on a certain trait, then that trait is assumed to be more influenced by heredity. But if identical twins and fraternal twins from similar environments do not differ on a trait, then that trait is assumed to be influenced more by environment.In the adopting method, behavioral geneticists study children adopted shortly after birth. By comparing their abilities and personality traits to those o their adoptive family members with whom they live and those of their biological parents whom they may have met, researchers can disentangle the effect of heredity and environment (Plomin et al., 1988).Adoptive research has assembled the Minnesota Twin Registry, which in 1998 included over 20,000 twin pairs (Bouchard, 1998). Probably the best way to assess the relative contributions of heredity and environment is to study...
