Gunnar, M. R., Gonzalez, C. A., Levine, S. 1980. The role of peers in modifying behavioral distress and pituitary-adrenal response to a novel environment in year-old rhesus monkeys. Physiology and Behavior 25, 795-798.

Infant rhesus macaques were captured from their social group and placed in an unfamiliar environment for 24 hours either (a) alone or (b) with another infant from the same group. When tested alone, the animals exhibited significantly more signs of distress - agitation, distress vocalization - than when they were tested with a companion, indicating that the companion had a stress-buffering effect