Second, Belsky and Pluess (2009) made a strong case that the emphasis on risky environments overlooks the possibility that environmental sensitivity is evidenced at both ends of the spectrum. According to their differential susceptibility model, some individuals may be highly sensitive to their immediate social environments and not only will experience very poor outcomes in unhealthy environments but also will have exceptionally positive outcomes in healthy environments. Given this expected crossover association, a risky allele may be common because, on average, it does not confer a risk for the population; the allele may be risky in risky environments but protective in enriching environments. Recent work has shown that alleles within the dopaminergic (DRD4) and serotonergic (5HTTLPR) system confer genetic risks for externalizing behaviors on those in the most-risky environments but protective factors on those in the least-risky environments (Simons et al. 2011).
