Animals such as turtles with bony shells, spines, or venom age slower and sometimes hardly at all, according to new research.
Scientists found that these features are more important than a low metabolism – shedding fresh light on the aging process.
Turtle shells contribute to slower and even ‘negligible’ aging – or lack of biological aging, for example.
Many species of turtles and tortoises have also found a way to switch off senescent cells, which are ‘zombie’ cells that stop dividing and cause disease.
The senior author of a new study, Professor David Miller of Penn State University, said: “Negligible aging means if an animal’s chance of dying in a year is one percent at age 10, if it is alive at 100 years, it’s chance of dying is still one percent.
“By contrast, in adult females in the U.S., the risk of dying in a year is about 1 in 2,500 at age 10 and 1 in 24 at age 80.
“When a species exhibits negligible senescence, or deterioration, aging just doesn’t happen.”
Professor Anne Bronikowski of Michigan State University, a co-author of the study, said: “It could be their altered morphology with hard shells provides protection and has contributed to the evolution of their life histories, including negligible aging – or lack of demographic aging – and exceptional longevity.”
The oldest land creature in the world is a giant tortoise named Jonathan, which lives in the Seychelles Islands near the coast of East Africa, is believed to be 190 years old.
Professor Beth Reinke of Northeastern Illinois University, who was lead author, said: “These various protective mechanisms can reduce animals’ mortality rates because they’re not getting eaten by other animals.
“Thus, they’re more likely to live longer, and that exerts pressure to age more slowly.
“We found the biggest support for the protective phenotype hypothesis in turtles. Again, this demonstrates that turtles, as a group, are unique.”
The findings published in the journal Science shed fresh light on why an ‘elixir of youth’ has proved so elusive for humans.
The international team observed negligible aging in at least one species of frog and toads, crocodiles, and turtles.
Reinke added: “It sounds dramatic to say they don’t age at all, but basically their likelihood of dying does not change with age once they’re past reproduction.”
Data was collected from 107 populations of 77 wild species of reptiles and amphibians across the world in the most comprehensive study of aging to date.
The analysis showed turtles, crocodiles, and salamanders have particularly low aging rates, as well as extended lifespans for their sizes.
Miller said: “Anecdotal evidence exists that some reptiles and amphibians age slowly and have long lifespans, but until now no one has actually studied this on a large scale across numerous species in the wild.
“If we can understand what allows some animals to age more slowly, we can better understand aging in humans, and we can also inform conservation strategies for reptiles and amphibians, many of which are threatened or endangered.”
A technique called phylogenetics – which shows how genetically similar organisms are – was combined with observations of animals that were captured, tagged and released.
It enabled a comparison between cold and warm-blooded animals – ectotherms and endotherms, respectively.
The former rely on external temperatures and often have lower metabolisms. It was believed they age more slowly than endotherms which generate their own heat.
Miller said: “People tend to think, for example, that mice age quickly because they have high metabolisms, whereas turtles age slowly because they have low metabolisms.”
But ectotherms’ aging rates and lifespans were found to range both well above and below those known for similar-sized endotherms.
It suggests the way an animal regulates its temperature is not necessarily indicative of lifespan.
Miller said: “We didn’t find support for the idea a lower metabolic rate means ectotherms are aging slower.
“That relationship was only true for turtles, which suggests that turtles are unique among ectotherms.”
On the other hand, animals with physical or chemical traits that confer protection were found to live much longer for their size.
The study was a huge global enterprise involving 114 scientists looking at a wide variety of species.
Reinke said: “Being able to bring these authors together who have all done years and years of work studying their individual species is what made it possible for us to get these more reliable estimates of aging rate and longevity that are based on population data instead of just individual animals.”
All living organisms age and die – there is no way of escaping death. But they follow different patterns of weakening and deterioration – counterintuitive as it may seem.
Bronikowski: “Understanding the comparative landscape of aging across animals can reveal flexible traits that may prove worthy targets for biomedical study related to human aging.”
