Non-human primates share a great deal of phylogenic proximity to humans and exhibit similar behavioral and physiological responses to anxiety-producing situations. Through naturalistic and laboratory studies, researchers were able to identify a specific subgroup of monkeys that exhibited hyper-responsiveness to anxiety-promoting situations. These subjects shared behavioral features as well as biological changes, such as the dysregulation of hypothalamic-pituitary-adrenal (HPA) axis. The significance of maternal-infant attachment has been seen as a significant factor in the development and maturation of biological systems. Impaired attachment through parental deprivation, repeated separation, abuse, and disruption through unpredictable foraging demand leads to significant neurobiological and behavioral sequelae. Neuroimaging and functional studies have identified certain regions of significance, and together with lesion studies have provided insight into complex neural circuitry. Non-human primates have also aided in understanding resilience through exploration of stress inoculation and maternal-infant relation.