There are three Ways of dying: from injuries, illnesses or old age. Over time, people have gotten better at avoiding the first two, but as we age, senescence — the gradual deterioration of bodily functions with age — is inevitable. However, some species seem to do better than others: Take the hydra, a tiny freshwater creature that some scientists believe is potentially immortal. Last year, a naked mole rat made headlines when it lived to be 39 years old, five times the typical lifespan for similarly sized rodents. And just a few months ago, an Aldabra giant tortoise named Jonathan celebrated what is believed to be his 190th birthday, making it the world’s oldest living land animal.
Cases like this beg the question: is it possible to escape aging?
The authors of a study published in Science Last month you said yes. Well if you are a turtle. In a comprehensive analysis of 52 turtle species (a term that encompasses both aquatic and tortoiseshell turtles), the four-strong team of scientists found that the majority of them showed exceptionally slow — and in some cases negligible — senescence in captivity. That doesn’t make them immortal; Turtles can still die from disease or injury. But unlike birds and mammals, their overall mortality risk does not increase with age. “We have confirmed something that was suspected a long time ago but never proved,” says Fernando Colchero, a biodemographer at the University of Southern Denmark.
The aging rate is a measure of how a population of organisms becomes more at risk of dying as it ages. In birds and mammals, this risk is believed to increase exponentially with age. But for most turtle species in the study, that rate remained nearly unchanged no matter how old they got.
Colchero and his colleagues also found that the environment in which the animals lived played a role. “Based on comparing our results to those of animals in the wild, turtles and tortoises may actually change their aging rates dramatically as conditions improve,” he says, citing factors such as protection from predators, a controlled climate and unlimited access for food and shelter. This differs from previous work using primate data, which reported an increase in lifespan due to better living conditions but no significant reduction in mortality due to slowed aging.
What gives? Some evolutionary theories propose that senescence is the result of an energy compromise. Most mammals and birds stop growing once they reach sexual maturity, Colchero says. At this point, their energy is prioritized for reproduction rather than cell repair. Without adequate care to counteract wear and tear, the body becomes more susceptible to chronic age-related diseases, as well as injury or infection. “But many reptiles don’t do that. They keep growing, which means they seem to be very efficient at repairing damage and keeping the body’s functions working properly,” he says.
According to Rita da Silva, a biologist who led the study with Colchero, animals with this trait are the best candidates for escaping aging. This idea has been around since the 1990s, and to prove it, the researchers gathered demographic information from the Zoological Information Management System, a database of records from zoos and aquariums maintained by the nonprofit organization Species360. They selected species that had data for at least 110 animals and only focused on freshwater or terrestrial turtles.