Some people react more calmly in stressful situations than others. Certain genes, such as the so-called COMT gene, are thought to play a role in determining our stress response. Researchers have now studied this gene in macaques, a genus of Old World monkeys, and for the first time have shown that a specific variant of the gene is associated with higher excretion of the stress hormone cortisol. The gene variant may also influence social rank among the animals.