Experts Make Surprising Discovery About Tortoises' Incredibly Long Life Span

Jonathan the Seychelles giant tortoise, who recently celebrated his 190th birthday, has surpassed Tu'i Malila's Harriet, a tortoise that passed away in 1965, to hold the title of "Oldest Living Land Animal." However, compared to the two, Adwaita, a giant tortoise from Aldabra was older than both of them. Unconfirmed rumors claim that Adwaita was born at the height of the Little Ice Age and passed away in 2006 at the ripe old age of 255 from an infection brought on by a crack in his shell.

There are other cold-blooded animals with unusually long lifespans besides tortoises. The tuatara, a lizard-like reptile with a line of spikes running down its spine, can live well over a century, and the blind cave salamander, an amphibian withvery poor eyesight nearly translucent skin, can live to be over 70.

David Miller, a professor of wildlife population ecology at Penn State, said that there is anecdotal evidence that some reptiles and amphibians age slowly and live a long time, but no one has examined this issue extensively across many species in the wild before. According to Miller, knowing what causes some animals to age more slowly can help us understand aging in humans. Miller also noted that since many reptiles and amphibians are threatened or endangered, the knowledge could be used to develop conservation strategies for these species.

Miller and an international team of 113 scientists conducted the largest study of aging and longevity to date, using information gathered from 77 species of wild reptiles and amphibians over 60 years. Their goal was to identify the factors that affect rates of aging. The researchers discovered that the animals that aged the slowest had defense mechanisms against predators. Amazingly, animals with hard shells, like turtles and tortoises, barely aged at all, refuting the notion that aging is a natural part of evolution.

Thermoregulatory Hypothesis

The thermoregulatory hypothesis, which contends that creatures with a higher metabolic rate age more quickly, was put to the test by Miller and his team. This theory holds that warm-blooded animals age more quickly because of their high metabolisms, which they depend on to produce heat. On the other hand, cold-blooded animals absorb heat from their surroundings, which results in a slower metabolism and slower aging.

However, the team's findings show that cold-blooded animals age at much more varied rates than previously believed. On the one hand, some cold-blooded animals appeared to age absolutely nothing. To put it another way, the animals' risk of death did not rise with age, which is a characteristic shared by only one warm-blooded animal, the naked mole-rat.

On the other hand, compared to one of the warm-blooded animals that age the fastest, the impala, a dozen of the cold-blooded species aged four times more quickly. This suggested that more than just controlling body temperature is responsible for the variation in aging rates between species.

Read also: 29 Countries in the World With the Longest Life Span 

Protective Phenotype Hypothesis

The protective phenotype hypothesis, a less well-known theory that contends that animals with protective traits, such as a shell or venom, have slower aging, was investigated by the researchers to solve this mystery. Beth Reinke, the first author of the study and expert in evolutionary biology explained that because they are not being eaten by other animals, these various protective mechanisms can lower the mortality rates of animals. They are under more pressure to age more slowly because they have a higher chance of living longer, Big Think reports.

Physical protection, such as armor and shells, and chemical protection, such as skin toxins and venom, were both categories of protection taken into consideration by the researchers. When comparing only species with cold blood, those with physical protection aged five times slower than those without it, and those with chemical protection aged twice as slowly.

This finding is unlikely to lead to the discovery of an anti-aging cream that makes humans grow a shell like a tortoise. However, the study allows a more comprehensive portrait of aging across animals, human aging included.

Related article: Axolotls Life Span: Are These Giant Salamanders That Can Regenerate Body Parts Going Extinct?