The fundamental question addressed in this dissertation is the extent to which variability in kin and social relationships affects the phenotypic expression of biological indicators of health status. To achieve this goal, I applied the theories of kin and social investment popularized in evolutionary ecology to a study sociality and health in Mandeville, Jamaica. This research employs ethnographic and biometric methods to test hypotheses regarding the relationship between kin and social networking and variability in health outcomes. Using ethnographic methods, I identified culturally salient aspects of social and kin relationships. This diversity in methodology reflects my application of a biocultural model. Kin relationships were studied within the context of the home. In an examination of the impact of household composition on health, I found that individuals living with family members of variable degrees of relatedness had higher body mass index values than individuals living alone or with friends, and individuals living with nuclear family members. However, household composition did not impact variability in skinfold thickness. Furthermore, household composition was not related to variability in Epstein Barr virus antibody titer levels, which suggests low incidence of recent psychosocial stress. To investigate social investment and health, I first examined the impact of participant involvement in conjugal unions of variable type and duration on health. Type of conjugal union was not a predictor of health outcomes. However, individuals who were involved in short-term unions had lower body mass index values and Epstein Barr virus antibody titer levels than single individuals and individuals in long-term unions. This suggests that individuals in short-term unions experienced better health than their counterparts. I also explored the impact of friendships on health outcomes. While visits with friends did not impact health outcomes, number of friends did predict variability in health outcomes. Individuals reporting 5-10 close friends had higher Epstein Barr virus antibody titers than individuals with both fewer and more friends. These findings together permit the following conclusions: (1) kin investment impacts health in variable household environments, and (2) negative investment in social relationships is reflected in excessive weight gain and high psychosocial stress.