Nature vs Nurture in IQ z Are differences

Nature vs. Nurture in IQ z Are differences between people due to environmental or genetic differences? z Misunderstanding the question y“Is a person’s intelligence due more to genes or to environment? ” yno genes = no intelligence yboth genes & intelligence crucial for any trait 1

Nature vs. Nurture in IQ z Rectangle analogy y is a rectangle’s area due more to its width or its length? y are differences in area among rectangles due more to differences in their length or in their width? Length Group B Length Width Group A 2

Heritability & Environmentality z Heritability ydegree to which variation in trait stems from genetic, rather than environmental, differences among individuals z Environmentality ydegree to which variation is due to environmental rather than genetic differences 3

The Heritability Coefficient z Single number, ranging from 0 to 1. 0 z Represents amount of trait due to genetic differences z 0 means no variance due to genetics z 1 means all variance due to genetics z. 30 means 30% is due to genetic differences, 70% due to environmental 4

Twin Studies & Family Influence z If trait genetic: y closely related more similar than less closely related z Many close relatives share environments too z Types of studies to separate effects y monozygotic twins reared together y monozygotic twins reared apart y siblings/dizygotic reared together y siblings/dizygotic reared apart y adoptive siblings reared together 5

Family Influence on IQ z Transient influence of family in which you are raised y adoptive siblings as children and adults y identical vs. fraternal twins reared together Identical twins Fraternal twins 6

IQ Differences among Racial/Cultural Groups z Find differences among racial & cultural groups on IQ y. American Blacks score about 15 points lower than Whites z WHY? ygenetics? x. Witty & Jenkins (1935) x. No support for genetic differences yenvironment? 7

IQ Differences among Racial/Cultural Groups z Each wheat field planted from same package of genetically diverse seeds z One field is quite fertile, the other is not z Within each field, differences due to genetics z Between each field, differences due to environment (fertility) 8

Why differences between Blacks & Whites? z Social designation influences yautonomous minorities xdeliberately separate themselves yimmigrant minorities xcame to country to better lives xsee selves as better than those left behind yinvoluntary minorities xdid not choose minority status xroutinely judged as inferior by dominant majority xcross-cultural findings on IQ scores 9

Historical increase in IQ z Improved performance on IQ tests over the IQ years Scores z Big increases in tests assessing fluid intelligence, smallest in factual knowledge z Increased schooling only accounts for small portion of this increase z Due to changes in the culture? Year 10

Summary z Nature vs. nurture debate yheritability vs. environmentality ystudies of twins & family influence z Racial & cultural differences in IQ ywhy we can’t interpret differences as due to genetics ywhat we can attribute the differences to z Historical increase in IQ scores 11