Human life histories and demographic outcomes are impacted by kin behavior in many ways, and human evolutionary theory is essential to understanding how environmental context and kin relationship moderate this behavior in either cooperative or competitive directions. However, kin presence is simultaneously correlated with these behavioral factors, as well as non-behavioral factors such as risk of infection or familial wealth. As such, it can be hard to disentangle evolutionarily driven effects from other factors correlated within a family. In this chapter we document how historical family reconstitution databases have assisted in the investigation of kin effects, and outline their advantages in disentangling these behavioral kin effects from non-behavioral accompanying factors. Along the way we introduce several of these family reconstitution studies, describe their ability to separate unobserved heterogeneity in kin effects across families, and document the importance of evolutionary theory in understanding kin effects across different populations.