Why Do Giant Tortoises Live So Long?

Sorry hares, but giant tortoises are still winning the race of life by treating it like a marathon and taking each lap slow and steady. The oldest living giant tortoise known to science (and the oldest animal in the world) is Jonathan, a 184-year-old that lives on St. Helena Island. Unofficially, there have been claims of older tortoises, including one believed to have been 255 when it died in 2006. Researchers have not been able to pin down exactly what keeps them around for so long, but their slow-motion lifestyle may have something to do with it.

Giant tortoises have very slow metabolisms, which means they burn energy at a slower rate than smaller and faster animals. In 1908, physiologist Max Rubner introduced the rate of living theory, which suggested an inverse correlation between metabolism and lifespan (the faster the metabolism, the shorter the life). Scientists have had some issues with the theory over the past century (some argue that metabolism is a “poor measure of energy expenditure”), and it has largely been discredited, but it did spawn the phrase “Live fast, die young,” and it serves as the basis for expanded research on the topic.

The link between metabolism and longevity is still not understood, but some scientists believe that metabolism is linked to the creation of free radicals, unstable molecules that damage cells and that increase as more energy is burned by the body. According to this theory, tortoises live longer because their slow metabolisms burn less energy, which means less harm to the cells in their bodies.

Theories on aging alone don’t fully explain how tortoises live much longer than humans, but their reproductive lives and size may hint toward an explanation. Because of their built-in home security system (the massive hard shells) and their geographic isolation (they only live on a few specific islands), giant tortoises have very few predators to worry about. Besides simply not becoming prey, this means that giant tortoises don’t have to rush into reproduction to keep their species alive. The tortoises essentially reserve their biological resources to keep themselves alive—they needn't rely on them to aid procreation while they’re young.

Each theory has its flaws and unanswered questions, but scientists believe that some combination of biological and evolutionary factors is what keeps giant tortoises alive for so long. There is no magical gene that humans can harvest and exploit, but that hasn’t stopped us from looking.