Human outcomes are determined by a complex interplay of biological and social  processes. Biosocial Interactions—the newest of OPR’s primary research areas—focuses on three principal topics: allostatic load, epigenetics, and telomere length.

It has long been known that exposure to stress increases allostatic load through the release of cortisol and other steroids into the bloodstream. When exposure to stress becomes chronic (for example, because of violence and instability within families, neighborhoods, or schools), an excessive allostatic load may be produced with far-reaching negative effects on health, behavior, and cognition (Goldman; McLanahan, Notterman).

New scientific work also indicates that genes are not simply inherited and automatically expressed, but are turned on and off  through interactions with the environment. For both animals and human beings, the critical environment is social, and exposure to advantage or disadvantage because of one's structural position in society can strongly affect gene expression (Conley; Altmann). Indeed, research indicates that methylation triggered by environmental interactions may permanently modify genetic material in ways that can be inherited.

Finally, research on telomeres illustrates how exposure to stressful environments can affect health and wellbeing at the chromosomal level. Telomeres are nucleotide sequences found at the ends of each chromatid. They protect the ends from deterioration and possible mingling with other strands of DNA or RNA. With repeated cell divisions in the course of normal aging, telomeres are progressively shortened, thereby increasing the likelihood of abnormal outcomes and adverse medical conditions. Exposure to chronic stress is another factor that can hasten the shortening of telomeres.