A study of rhesus macaque monkeys may have solved a long-standing puzzle on a link between social rank and health.A study of 10 social groups of macaque females showed that the activity level of an individual's immune genes was an accurate predictor of her social rank.In a paper in Proceedings of the National Academy of Sciences, the team also showed that the monkey's immunity changed when social rank was altered.The work suggests that status drives immune health, rather than vice-versa. A great many studies have shown associations in both humans and non-human primates between social environment and biological markers of health. In previous studies of rhesus macaques, the so-called dominance rank has been correlated to levels of the stress-linked glucocorticoid hormones, sex hormones, the brain chemicals serotonin and dopamine, and white blood cell counts. But one unanswered question concerns cause and effect: does a compromised immunity or...