Somewhere beneath the icy waters of the North Atlantic, an ancient shark glides through the darkness at a pace slower than most humans walk. It moves with little urgency, beating its tail only a handful of times per minute. Some of these sharks may have been alive when Galileo was still studying the night sky while other individuals may have already been swimming through Arctic waters before the United States even existed.
And somehow, their hearts are still working.
Meet the Greenland shark, Somniosus microcephalus, if you haven’t heard of it already. They have become one of the most fascinating animals in aging research since being crowned the longest-living known vertebrate on Earth, capable of surviving for at least 272 years with some individuals estimated to approach 400 years old. In fact, they mature sexually at roughly 150 years old, an age at which most vertebrates would have long since died. And while these massive sharks can exceed 16.5 feet (five meters) in length, they only grow only about one centimeter per year. They are an enigma, to say the least. Scientists have spent years trying to understand how an animal — this animal — can survive for centuries, and a new study has now added another layer to the mystery that surrounds these predators by looking directly at their heart.
What they found was surprising, and in many ways counterintuitive because the sharks showed many of the classic hallmarks of aging that scientists usually associate with declining health. In humans and other vertebrates, aging hearts typically accumulate scar-like collagen deposits called fibrosis. Cells become damaged by oxidative stress, waste products build up inside tissues, and over time these changes can stiffen the heart, disrupt electrical signaling and reduce the organ’s ability to pump blood efficiently. The Greenland shark heart showed all of this! Led by Dr. Elena Chiavacci, the research team found widespread fibrosis throughout the sharks’ heart tissue and they also detected massive amounts of lipofuscin, often nicknamed the “aging pigment.” Lipofuscin is essentially cellular garbage (clumps of oxidized proteins and fats that cells can no longer break down). In humans, its accumulation is strongly linked with aging tissues.
Under the microscope, the Greenland shark heart looked ancient. Yet the sharks themselves did not appear to be failing. The individuals sampled for the study had been actively swimming, hunting and taking bait before capture! Their heart tissue showed no signs of acute injury or widespread cell death! Despite carrying what looked like centuries’ worth of molecular wear and tear, these animals were still functioning.
How?
For decades, aging research has often focused on preventing damage. The prevailing assumption has been that long-lived animals succeed because they somehow avoid oxidative stress, avoid tissue degeneration or maintain perfectly “young” cells over time. But the Greenland shark may point toward a different possibility entirely: maybe longevity is not always about resisting damage but about tolerating it. This idea is known as “resilience.” In medicine, “resilience” refers to the ability to maintain function despite stress or injury; some human centenarians provide a version of this phenomenon, showing that while their bodies may still accumulate age-related diseases or molecular damage, they continue functioning far longer than expected. The Greenland shark appears to take this concept to an… extreme.
The study also compared Greenland sharks with two other species: the velvet belly lantern shark (Etmopterus spinax), a much smaller deep-sea shark that lives only around a decade, and the African turquoise killifish (Nothobranchius furzeri), one of the shortest-lived vertebrates known. Neither species showed the same dramatic cardiac fibrosis or massive lipofuscin buildup seen in Greenland sharks. So these traits are not simply a consequence of living in deep water or being a fish — instead, they may be linked specifically to extraordinary longevity.
Even more intriguing was the evidence of oxidative stress. The researchers found strong deposits of 3-nitrotyrosine, a molecular marker associated with cellular damage caused by reactive oxygen species. Oxidative stress has long been considered a major driver of aging. The traditional theory predicts that exceptionally long-lived animals should either produce fewer damaging molecules or possess stronger antioxidant defenses. But Greenland sharks seem to accumulate oxidative damage anyway, which mirrors findings in another famously long-lived species, the naked mole rat. They, too, also tolerate surprisingly high levels of oxidative stress! Both of these animals challenge the idea that longevity depends on keeping cells pristine. Instead, they suggest that some species may simply be better at surviving with damage. And that could have enormous implications in human health. See, human hearts become stiffer with age partly because of fibrosis (i.e., our cells accumulate damaged proteins and dysfunctional mitochondria over time). So what if the real key to healthy aging is not eliminating those processes entirely, but preventing them from triggering catastrophic decline? Aging itself might not be the problem.
Of course, there are still major unknowns. Scientists do not yet know exactly how Greenland shark hearts continue functioning despite these changes. The animals’ slow metabolism, low blood pressure and sluggish lifestyle may reduce strain on the cardiovascular system. Not to mention their unusually flexible blood vessels could also help compensate for stiffening heart tissue. There may also be molecular tricks we have not discovered yet! After all, researchers still know remarkably little about the biology of Greenland sharks due to them living in one of the most difficult environments on Earth to study. So every new piece of information feels less like solving a puzzle and more like realizing how large the puzzle actually is. Still, this new work suggests that aging and decline are not necessarily the same thing, which is exciting because for us humans, “growing older” is often framed as an inevitable story of deterioration. The Greenland shark shows that’s not necessarily the case.
What’s that saying, “489 is the new 30”?
