Racial differences in heritability estimates for tests of spatial ability.

Abstract

172 pairs of MZ twins and 112 pairs of like-sexed DZ twins were given a battery of psychological tests which included Surface Development Test, Porteus Mazes, Newcastle Spatial Test, Paper Folding Test, Identical Pictures Test, Perceptual Speed, Object-Aperture Test, Form B, and Cube Comparisons. 242 were boys and 326 girls, of whom 482 were white and 86 Negro. Ages ranged from 13 to 18 yr. Using four different heritability ratios the relative intrapair similarity of MZ and like-sexed DZ twins on selected spatial tests was determined. Although the MZ and DZ intraclass rs are generally higher for the white than for Negro children the heritability estimates which are determined by rMZ rDZ differences are higher for the Negro pupils. Environment does not play a more significant role in the development of spatial ability of Negro children than of white children.