[♪ INTRO ].

Turtles live a ridiculously long time. The oldest known turtle—a Seychelles giant tortoise named Jonathan — is 186 years old and still kicking!

Galapagos tortoises have produced healthy, viable young past their 80th birthday. And even smaller species can live for half a century, as long as they aren’t eaten or run over first. Scientists aren’t 100% sure how these animals live so long — but a lot of it seems to boil down to preventing wear and tear to the body.

In most species, including ours, the odds of dying go up as you get older. That’s because our bodies just kind of deteriorate over time. Like any machine, parts slowly wear down, and that eventually leads to some kind of catastrophic failure.

But that’s not always the case in turtles — in some, being old means they’re less likely to croak. And they can even still have healthy offspring. This ability to stay alive and have healthy babies despite being old is called negligible senescence.

And though some of the details are still unclear, it seems turtles pull this off thanks to a remarkable tolerance for oxidative stress. That’s the harm to cells that happens due to reactive oxygen species or

ROS: a family of oxygen-containing compounds that really, really like interacting with other molecules. The accumulation of this damage, especially to neurons and immune cells, is thought to drive aging. But reactive oxygen species aren’t evil — they’re produced all the time, like in the calorie-burning process that turns food into cellular fuel. So the key is not getting rid of ROSs, but keeping them under control.

One of the ways turtles do that is by producing less of them. They have a slow metabolism, which means they need fewer calories than other animals of similar size. It also helps that they’re poikilothermic: their bodies can function at a wide range of temperatures.

So they’re not as stressed by cold or hot temperatures as we are—and less stress means less ROS. They also have ways to manage the ROS they do produce. Since these compounds can damage telomeres — the protective caps of DNA that shorten every time a cell divides — turtles produce lots of the enzyme telomerase, which helps prevent that shortening.

And that helps keep their cells healthier longer, lessening their odds of developing cancer or other diseases. They also make lots of strong antioxidants and other proteins that fight cellular damage. While these traits might seem like the perfect adaptations for a long and healthy life, biologists think they arose for another reason: surviving without oxygen.

Many turtles, including those cute red-eared sliders you might have seen in pet stores, can go weeks without breathing air — a handy trick if you want to spend the winter in an icy pond. They have special ways of keeping important tissues alive during that time, like shutting down oxygen-hungry neural circuits. But they also have to deal with the burst of ROS production that happens when they finally come up for air and oxygen levels rapidly rise — which is where those antioxidants and cell-healing proteins come into play.

So their longevity might be a happy side effect — one that some researchers are hoping to translate into longer, perhaps even indefinite lives for people. But... we can’t really replicate all of their tricks, like becoming poikilothermic. So while studying turtles may help us maintain fitness in later years, if you’re hoping they hold the secrets to immortality… well, I wouldn’t hold your breath.

Thanks for asking! And thanks to our patrons on Patreon, who keep the answers to questions like this flowing. If you want to pose questions like this, help us decide which ones to answer, or just get some cool rewards that you can’t get elsewhere, you can head on over to Patreon.com/SciShow to learn more. [♪ OUTRO ].