Why Greenland sharks live for four centuries

HostMost of us think of a long life as maybe eighty or ninety years, but in the deep, cold waters of the North, there's a shark that's just getting started at that age. It turns out we can actually tell how long they have been around by looking deep into their eyes, where they keep a piece of their past perfectly preserved for hundreds of years. How's it even possible for a set of eyes to act like a diary of a shark's entire life?

GuestIt's a bit of a detective story. Most fish have bones or scales that grow in layers, almost like the rings inside a tree trunk. You count the rings, and you get the age. But these sharks are soft. They're made of gristle rather than bone, so they don't leave those kinds of tracks. For a long time, people just had stories and guesses. Then some researchers realized the answer was literally hiding in the shark's eye lens. The very center of the lens is a biological time capsule. It's made of proteins that are formed while the shark is still a tiny pup in the womb. Once those proteins are set, they're never recycled or replaced. They stay there, locked away, for the rest of the shark's life.

HostBut wait, how do you get a date from a tiny bit of protein? I thought carbon dating was for things that had been dead for thousands of years.

GuestIt usually is, but they had a lucky break because of the nineteen fifties. When countries were testing nuclear bombs in the ocean, it left a very specific mark in the world’s carbon levels. It's called the bomb pulse. If a shark has that specific mark in its eye, we know it was born after those tests. If it doesn't, it's older. By using that as an anchor, they found sharks that were easily three or four hundred years old. The wildest part is that they don't even reach sexual maturity until they're about a hundred and fifty. They effectively spend a century and a half just being kids before they're even ready to have pups of their own.

HostA century and a half of childhood is hard to even imagine. But what keeps them from just wearing out? Most things that live that long are like trees, not animals that have to swim and hunt.

GuestIt mostly comes down to where they live. They stay in water that's right near the freezing point. There's a rule called the Arrhenius law, which basically says that the rate of chemical reactions is dictated by temperature. If you turn down the heat, the way the body works slows way down. They're living in a giant natural refrigerator. Because they stay so cold, they have a very low metabolic rate. When a body burns energy fast, it creates these little harmful bits of oxygen called free radicals. Those bits bounce around and beat up your DNA, which is a big part of why we age. But because these sharks have such a slow inner engine, they produce way less of that cellular trash.

HostI read they move pretty slowly too, like they're almost drifting. Is that part of the same trick?

GuestAbsolutely. They're the slowest-moving sharks in the ocean. They cruise at about zero point seven miles per hour, which is way slower than a person walks. And that lack of effort goes all the way down to their internal organs. A Greenland shark’s heart only beats once every ten or twelve seconds. Compare that to a human heart, which beats about once every second. That minimal workload prevents the heart damage and wearing out of tissue that usually leads to heart failure in other species. Even their muscle enzymes stay stable and keep working for centuries. It means a shark that's three hundred years old is often just as physically capable as one that's only fifty.

HostSo they're not just moving in slow motion, they're actually not breaking down at all. Most animals eventually hit a point where everything just starts to fail, right?

GuestNormally, yes, but these sharks have what biologists call negligible senescence. It means they don't really seem to age in the traditional sense. They don't get weaker or more likely to get sick as the centuries pass. This is likely because they're masters of high-fidelity maintenance. Their bodies have incredibly good DNA repair systems and special helpers called protein-folding chaperones. These helpers act like a cleaning crew that prevents cellular garbage from building up. When they looked at the shark's genome, they found unique ways the animal handles tumor suppression and keeps its DNA in top shape. They prioritize constant repair over fast growth or high speed.

HostSo it's a trade-off. They give up the ability to move fast or stay warm, and in exchange, they get a body that just refuses to quit.

GuestThat's it. They have found a way to stay at the peak of their health for longer than most human empires have lasted, simply by living in the slowest lane possible.

HostIt's a whole different way of existing, knowing that while our world changed so much, that shark was swimming through the dark with its eyes still holding onto the same bits of itself from the very start.