When Hurricane Maria hit Puerto Rico in September 2017, the worst storm in the island’s recorded history left a trail of devastation in its wake. Nearly 3,000 people died in the immediate aftermath, while many survivors were left without homes and electricity. Neighbouring Caribbean islands suffered similar destruction. One of those islands, whose only residents are a colony of rhesus macaques, is the tiny Cayo Santiago.

There are long-term health implications for people who live through traumatic events. Studies have shown that survivors are at a higher risk from age-related illnesses such as heart disease, but it isn’t really understood how these events translate into morbidities decades down the line. Ethically, and due to the unpredictability of such events, research into the health impacts of natural disasters is challenging. The generations of monkeys on Cayo Santiago, however, have been studied since they were first introduced to the island in 1938, offering a unique insight into how an extreme-weather event might affect them – and, by inference, us.

Rhesus macaques are the most commonly studied monkey in medical research. As our close genetic relatives, they share many of the same behavioural and biological features, and their bodies age in very similar ways, only across a lifespan of just a quarter the length of ours. By analysing blood samples from the four years prior to Hurricane Maria and from a year after, new research from an international team of scientists suggests that the biological age of the monkeys that survived had increased by an average of two years – roughly seven to eight years in a human lifespan.

From the samples collected after the hurricane hit, the researchers noted changes in up to four per cent of genes compared to samples taken prior. Specifically, the genes disrupted were those associated with inflammatory responses and the proper functioning of proteins in cells, a change that’s seen naturally in both monkeys and humans as they age. ‘At a molecular level, we found that survivors of the storm were a little bit older than they should have been, hinting that experiencing this storm might recreate or accelerate the ageing process,’ Rhesus macaques on Cayo Santiago says Marina Watowich, a researcher at the University of Washington and lead author of the study. She explains that this increase in biological age was quite a big change, ‘more than what we would have expected’.

Not all of the animals responded in the same way. Some appeared many years older, some didn’t appear older at all, and it’s what’s driving that variation that Watowich says is one of the next questions they want to answer, particularly when faced with a future in which, as a result of climate change, the frequency and strength of extreme-weather events is increasing.

‘If we can identify populations that are more at risk,’ adds Noah Snyder-Mackler, one of the study’s co-authors, ‘then we could quickly target social interventions or other buffering mechanisms to try to help them as soon as possible after the storms.’