The study of brothers and sisters from adoptive and biologically related families permits unique analyses of the determinants of young adults' educational and occupational achievements. Brothers and sisters come from the same homes, neighborhoods, and usually schools. Many differences among families are controlled by the study of siblings. In addition, adoptive families influence their children only through the environment they provide, whereas biologically related parents transmit their intellectual and personal characteristics to their offspring genetically as well. Thus, the comparison of models of adult achievements for children from adoptive and biologically related families can inform us about the true effects of family environments, apart from genetic transmission (Scarr and Weinberg, 1978, 1980). In this follow-up study of 450 biologically related and adopted young adults (ages 22 to 30 years), we report on the family resemblances in educational and occupational achievements. Parents' reports were obtained on 97% of the original sample (N = 443), and 77% of the young adults participated in the follow-up study themselves; complete educational and occupational data were available on 303 young adults. Results show that biological sons are more influenced by their family backgrounds than daughters, regardless of genetic relatedness. A second finding is that young women's achievements are not as predictable from their own earlier achievements as are those of their brothers. A third finding is that parents invest in their sons' educational futures, regardless of sons' abilities and achievements, in ways they do not invest in their daughters' postsecondary educations. Sibling correlations and natural mother-adopted child correlations suggest that test scores, high school performance, postsecondary education, and even later occupational status can be influenced by genetic variability in personal characteristics that affect such achievements.