We know, for example, from studies of adopted-out identical twins,190 that culture can produce a fifteen-point (or one standard deviation) increase in IQ (roughly the difference between the average high school student and the average state college student) at the cost of a three-standard-deviation increase in wealth.191 What this means, approximately, is that two identical twins, separated at birth, will differ in IQ by fifteen points if the first twin is raised in a family that is poorer than 85 percent of families and the second is raised in a family richer than 95 percent of families.
