Recent research with both humans and rhesus monkeys has provided compelling evidence of gene-environment (G x E) interactions throughout development that involve early attachment relationships. For example, a specific polymorphism of the serotonin transporter (5-HTT) gene is associated with deficits in infant neurobehavioral functioning, poor control of aggression and low serotonin metabolism during juvenile and adolescent development, and excessive alcohol consumption in early adulthood in monkeys reared with peers but not in monkeys reared by their mother. One interpretation of these findings is that secure attachment relationships somehow confer resiliency to individuals who carry alleles that may otherwise increase their risk for adverse developmental outcomes (“maternal buffering”). Similar patterns of apparent “maternal buffering” have been demonstrated for G x E interactions involving several other genes with functionally equivalent polymorphisms in both humans and rhesus monkeys. Recent research has suggested that much of this “buffering” may be taking place in the context of early face-to-face interactions between rhesus monkey mothers and their infants. Moreover, the allelic variation seen in these genes in rhesus monkeys and humans but apparently not in other primate species may actually contribute to their remarkable adaptability and resilience at the species level.