In a sample of Korean adoptees who have been quasi-randomly assigned to US adoptive families and who have been genotyped, we examine the influences and interplay of genetics (“nature”) and shared family environment (“nurture”) on a suite of outcomes. We use molecular genetic data to construct polygenic indices (PGIs) that partially predict the outcomes and examine the effects of the PGIs as well as those of a rich set of family variables. We also compare the resemblance of adoptive and biological siblings to decompose outcome variation into shares due to nature and nurture. We find that both nature and nurture causally affect most outcomes and that the influence of the PGIs tends to be of a similar magnitude to that of the observed family variables. Nurture appears particularly important for education, income, and nicotine usage, while nature has a particularly strong influence on GPA, soft skills, cognitive performance, BMI, and height. Nurture effects on education and smoking are partly traceable to rearing parents’ genetics. We investigate interactive effects and obtain suggestive evidence that family socioeconomic status and genetic propensity for educational attainment may be substitutes in the human capital production function for cognitive skills.