Contemporary legal and scholarly debates emphasize the importance of biological parents for children's well-being. Scholarship in this vein often relies on stepparent families even though adoptive families provide an ideal opportunity to explore the role of biology in family life. In this study, we compare two-adoptive-parent families with other families on one key characteristic — parental investment. Using data from the Early Childhood Longitudinal Study, Kindergarten-First Grade Waves (ECLS-K), basic group comparisons reveal an adoptive advantage over all family types. This advantage is due in part to the socioeconomic differences between adoptive and other families. Once we control for these factors, two-adoptive-parent families invest at similar levels as two biological-parent families but still at significantly higher levels in most resources than other types of families. These findings are inconsistent with the expectations of sociological family structure explanations, which highlight barriers to parental investment in nontraditional families, and volutionary science's kin selection theory, which maintains that parents are genetically predisposed to invest in biological children. Instead, these patterns suggest that adoptive parents enrich their children's lives to compensate for the lack of biological ties and the extra challenges of adoption.