Estimation of the direction and intensity of natural selection in relation to human intelligence by means of the intrinsic rate of natural increase

Abstract

A follow‐up study was made of 979 white individuals born in 1916 or 1917 who took the Terman Group Intelligence Test in the sixth grade while attending the Kalamazoo Public School System. It is the first study to take into account all of the variables that affect population growth (fertility, mortality, and generation length) by means of the intrinsic rate of natural increase when estimating the direction and intensity of natural selection in relation to human intelligence. When all the variables affecting population growth have been taken into account, the population under study has probably been in equilibrium with respect to the genetic factors favoring high intelligence, or more likely, has experienced a slight increase in the frequency of the genetic factors favoring high intelligence.