Twin resemblances in cognitive abilities in an Egyptian sample.

Thirty-six pairs of monozygotic (MZ) twins, 24 pairs of same-sexed dizygotic (DZ) twins, and 33 pairs of opposite-sexed DZ twins 12 to 19 years of age were tested in Minia, Egypt, on a battery of cognitive abilities tests. For most of the tests and composite scales, DZ resemblances were higher than typically found in Western samples and not significantly different from MZ resemblances. MZ resemblances were generally lower than typically found in Western samples. These results were discussed in terms of the influence of cross-cultural differences in degree of social stratification and assortative mating.