Lecture 5.doc

• Intelligence • Intelligence = general cognitive ability; Spearman’s g, the substantial covariation among diverse measures of cognitive ability; the general factor that typically accounts for about 40% of the total variance of diverse cognitive tests • More is now known about the genetics of individual differences in intelligence than about any other trait, behavioral or biological • Heritability • Heritability = the proportion of observed trait variance in a group of individuals that can be accounted for by genetic variance • At the level of the individual there is no nature-nurture debate; only at the population level can we disentangle genetic and environmental effects • Indexed by heritability quotient range from 0 to 1. 1 means trait is influenced solely by inheritance and 0 means trait is not influenced by inheritance. • Twin Studies • Out of 83 births, approx. 1 pair of twins are born. • Are identical (MZ) twins more similar to each other than fraternal (DZ) twins? • If twins are no more similar than fraternal twins, then genetics does not play a significant role in heritability and so on. • Heritability = 2(r mz– rdz • One limitation of twin studies is their assumption of equal environments • Adoption Studies • To whom are adopted children more similar — their biological or adoptive parents? • If a child resembles adoptive parent more than biological parent than there is an environmental role in the determination of an individuals character. • Adoption studies circumvent the assumption of equal environments • One limitation of adoption studies is their assumption of unequal environments • Genetics • In studies of more than 10,000 twin pairs: • MZ twin r = .86 • DZ twin r = .60 • MZ twins remain alike whether they are raised together or rai