The oldest living land animal in the world is named Jonathan, and he is a 190-year-old Seychelles giant tortoise. Jonathan and other cold-blooded species like his are famous for living outstandingly long lives. They age incredibly slowly, and new research suggests that some might not age at all. 

Negligible aging

Combined research from Michigan State and Penn State collected data from 107 populations of 77 species of reptiles and amphibians across the world. For the first time, they can declare that turtles, salamanders, and crocodilians have very slow aging rates for their sizes. Turtles especially have longer lifespans because of protective phenotypes like hard shells, and some of them even have what’s called negligible aging. 

“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,” said David Miller, senior author and associate professor of wildlife population ecology at Penn State.

The researchers observed these specimens through biodata and mark-recapture data where they caught and rereleased their specimens over the study period. Looking across their sample groups, they found that common traits such as their cold blood and low metabolisms didn’t account for certain turtles’ negligible aging. 

Protective phenotypes

Protective phenotypes – observable traits of an organism – such as hard shells, spines, or defensive poisons might be responsible for the negligible aging in some turtles. Researchers even found a case of negligible aging in each group of toads, frogs, and crocodiles. 

“Negligible aging means that if an animal’s chance of dying in a year is 1% at age 10 if it is alive at 100 years, its chance of dying is still 1% (1). By contrast, in adult [human] females in the US, 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 (deterioration), aging just doesn’t happen,” said Miller. 

These protective phenotypes protect animals from predation and other dangers. With the longer lifespans these afforded them they may have been able to further their evolution to age even slower. Research may be needed to find what exactly is the adaptation for negligible aging, but researchers believe it is these protective phenotypes that allow that to happen. 

“Understanding the comparative landscape of aging across animals can reveal flexible traits that may prove worthy targets for biomedical study related to human aging,” says Anne Bronikowski, co-senior author, and professor of integrative biology at Michigan State.