Chimpanzees stress less when a pal is around

Seeking out close mates during stressful times isn’t just a habit of us humans – chimpanzees, too, need a little help from their friends when they’re strung out.

Research published in Nature Communications suggests the apes in dangerous situations can keep stress hormone levels if friends are close by. If you’re a chimp, a spot of grooming from a loved one can also significantly reduce stress – and there are knock-on effects too.

“For animals, including humans, there is much evidence that individuals who maintain stable, close social bonds have greater reproductive success, increased longevity and better health compared with those who do not,” the research states.

Roman Wittig at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and colleagues measured the stress levels of 17 wild chimps in various situations, first with their friends in proximity, and then in the company of strangers – or rather, chimps without close social bonds.

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For the record, a “close social bond” between chimps was observed by mutual grooming, support and food-sharing between two individuals, maintained over several months – or even years. 

The team examined chimps in three scenarios: at rest, engaged in an everyday activity (such as grooming) and in a high-stress situation.

The latter was either naturally observed as chimpanzee bands crossed paths in the wild or created by playing the tree-drumming sounds of another group to simulate a rival encounter – a potentially life-threatening scenario for a chimp. 

In each of these experiments, the team observed levels of glucocorticoids – a class of stress-related hormones – by testing each chimpanzee’s urine. 

Their findings show that across all three scenarios, including the potentially lethal encounters, stress hormone levels weren’t elevated when bond partners were close by. 

Interestingly, glucocorticoid levels were at their lowest during grooming, but only if the activity involved a close friend. 

The researchers say this result echoes previous studies on humans, too, and has implications for health and survival.

The researchers say stress is a major cause of poor health and mortality in humans and other social mammals, partly because it can disrupt the activity of the hypothalamic-pituitary-adrenocortical axis – a complex set of interactions among the hypothalamus and pituitary gland, which are both in the brain, and the adrenal glands atop the kidneys.

The axis has major effects on vital functions such as the metabolic and cardiovascular systems.

The researchers say their results suggest “that regular and repeated, everyday affiliations have the potential to regularly and repeatedly re-align the [hypothalamic-pituitary-adrenocortical] axis throughout the day”.

The moral of the story? Any time is a good time to phone your mates.