References
- Loehlin , J. C. , Vandenberg , S. G. and Osborne , R. T. 1973 . Blood group genes and Negro‐white ability differences . Behav. Genet. , 3 : 263 – 270 .
- Osborne , R. T. and Suddick , D. E. 1971 . Blood type gene frequency and mental ability . Psychol. Rep. , 29 : 1243 – 1249 .
- Pakstis , A. , Scarr‐Salapatek , S. , Elston , R. C. and Siervogel , R. 1972 . Genetic contributions to morphological and behavioral similarities among sibs and dizygotic twins: Linkages and allelic differences . Soc. Biol. , 19 : 185 – 192 .
- Scarr , S. 1966 . Genetic factors in activity motivation . Child Devel. , 37 : 663 – 673 .
- Vandenberg , S. G. 1969 . A twin study of spatial ability . Multivar. Behav. Res. , 4 : 273 – 294 .
- Vandenberg , S. G. , Stafford , R. E. and Brown , A. M. 1968 . “ The Louisville Twin Study ” . In Progress in human behavior genetics , Edited by: Vandenberg , S. G. 153 – 204 . Baltimore : Johns Hopkins Press .