How Gene-Environment Interactions Shape Biobehavioral Development: Lessons From Studies With Rhesus Monkeys

Abstract

Recent research has found marked individual differences in patterns of rhesus monkey biobehavioral development throughout the life span. Approximately 20% of monkeys growing up in naturalistic settings consistently display unusually fearful and anxious-like behavioral reactions to novel, mildly stressful social situations throughout development; another 5%-10% are likely to exhibit impulsive and/or inappropriately aggressive responses under similar circumstances. These distinctive behavioral patterns and their biological correlates appear early in life and remain remarkably stable from infancy to adulthood. Both genetic and experiential mechanisms are implicated not only in the expression of these patterns but also in their transmission across successive generations of monkeys. For example, a specific polymorphism in the serotonin transporter gene is associated with deficits in infant neurobehavioral functioning and in juvenile and adolescent control of aggression and serotonin metabolism in monkeys that experienced insecure early attachments but not in monkeys that developed secure attachment relationships with their mothers during infancy (maternal buffering). Moreover, because the attachment style of a monkey mother is typically "copied" by her daughters when they grow up and become mothers themselves, similar buffering is likely to occur for the next generation of infants carrying that specific polymorphism.