A Greenland shark moves through the black water off Baffin Island at roughly one foot per second — about the pace of a person strolling through a supermarket aisle. Its heart beats once every twelve seconds. It grows a single centimetre a year. And it does not reach sexual maturity until it is about 150 years old, which means the animals now cruising the North Atlantic in reproductive prime were already alive when Isaiah Thomas was smuggling his printing press out of Boston in April 1775.
The species is Somniosus microcephalus, a name that translates roughly to ‘sleepy small-head’ — and it fits.
A body built for the long game
Everything about the Greenland shark is calibrated for slowness. According to reporting in Scientific American on a recent study led by Alessandro Cellerino at the Scuola Normale Superiore in Italy, the shark’s heart contracts once every twelve seconds, its cruising speed averages a single foot per second, and it adds about 0.4 inches of length per year. A 16-foot adult has therefore been growing, quietly, for something approaching four centuries.
That is not a metaphor. In 2016, an international team using radiocarbon dating of eye lens nuclei — the tissue laid down before birth and never replaced — estimated the maximum lifespan of the species at around 400 years, with a margin that placed the oldest individual sampled somewhere between 272 and 512 years old. It made the Greenland shark the longest-lived vertebrate ever documented.
Silicon Canals has covered how some of these sharks may have been alive when Isaac Newton was working out the laws of motion. The 150-year milestone before first mating is a smaller, stranger fact hiding inside that longer one.
What 150 years of adolescence actually means
Consider the arithmetic. A Greenland shark born in 1875 — the year Bizet’s Carmen premiered in Paris — is only now approaching the reproductive stage of its life. A shark that reached sexual maturity in the year 2000 was born around 1850, before the American Civil War. And a shark cruising the Davis Strait today, ready to mate, was likely born in the last decades of the 18th century.
The Battles of Lexington and Concord took place on 19 April 1775. Three days earlier, as recounted in WBUR’s account of Isaiah Thomas and The Massachusetts Spy, Thomas disassembled his printing press in Boston and had it ferried across the harbour to Charlestown, then hauled by horse-cart to a friend’s basement in Worcester. Somewhere between Baffin Bay and the Denmark Strait, in the same weeks that this was happening, sharks were being born that are only now — 250 years later — old enough to reproduce.
The slowness is the strategy
Photo by AKGodspeed on Pexels
Deep, cold water makes this pace possible. The shark spends most of its life between 200 and 600 metres down, in water hovering just above freezing. Cold slows everything: metabolism, cell turnover, oxygen demand, muscle contraction. A body operating at that thermal setting can afford to be patient in a way tropical fish cannot.
The species also has a genome unusually loaded with what researchers describe as anti-inflammatory, cancer-suppressing, and cellular-repair-related genes. According to coverage of the ongoing longevity research, that genetic profile is now a subject of active study for what it might reveal about the biology of ageing in humans.
But slowness comes at a cost. Cellerino’s team, examining heart tissue from sharks estimated to be between 100 and 155 years old, found that the muscle was, in fact, decrepit. Severe fibrosis. Scar tissue accumulation. Massive lipofuscin deposits inside cardiomyocytes — the age pigment produced when damaged cell machinery fails to clear itself. Oversize lysosomes. Damaged mitochondria. All the classic hallmarks of a very old heart.
And yet the sharks were caught on longlines, meaning they were still swimming, still finding bait, still hunting. According to research reported by Scientific American, scientists found that Greenland shark samples showed recognizable signs of aging at the molecular and tissue level. The research demonstrates that aging processes occur in the heart tissue of Greenland sharks, even as the organs continue functioning for centuries.
The heart ages. It just keeps working anyway.
How a battered heart keeps a shark alive for centuries
The Italian team’s best guess is a combination of low blood pressure and the peculiar structure of the shark’s ventral aorta, which may keep the heart muscle elastic even as scar tissue builds up inside it. A Greenland shark does not need to sprint. It does not need to pump hard. It ambushes seals asleep at the surface, scavenges polar bear carcasses, and drifts through the cold with an economy of motion that lets a scarred, stiff heart still do its job.
The comparison the researchers ran is telling. They put the shark’s heart tissue side by side with the velvet belly lantern shark — a small, deep-sea shark with a far shorter life — and the African turquoise killifish, a species biologists use precisely because it ages so fast. The aging markers piled up in the Greenland shark. They did not appear in the comparison hearts. Whatever the Greenland shark is doing, it is not avoiding cellular damage. It is tolerating it.
What a 150-year adolescence does to a population
The reproductive maths of this species is brutal in the face of modern fishing pressure. If a female cannot produce offspring until she is 150, then any population that gets thinned out by bycatch or targeted harvest cannot rebound on any timescale that means anything to a fisheries manager. A shark killed at age 80 has spent eight decades preparing to reproduce and never got the chance. A shark killed at 200 is only 50 years into its reproductive career.
Greenland shark meat is toxic when fresh — loaded with trimethylamine oxide, which the shark uses as an antifreeze in its tissues, and which breaks down into compounds that intoxicate anything that eats it. Icelandic hákarl, the fermented shark dish, exists because the meat has to be buried and cured for months before it becomes edible. That toxicity is probably the only reason the species has not been fished to collapse.
Individual sharks caught today were, as radiocarbon evidence has confirmed, alive before the Enlightenment. They swam under Arctic ice while Newton was writing the Principia, while Bach was composing in Leipzig, while the Committees of Safety were quietly stockpiling muskets in colonial workshops.
The eyes still work
These animals also carry a parasitic copepod, Ommatokoita elongata, dangling from each cornea, which long led people to assume the sharks were effectively blind. They are not — the parasite clouds the cornea but leaves the retina behind it intact, a story Silicon Canals has covered in detail separately.
A 250-year-old animal, drifting through black water at walking pace, with a scarred heart, a copepod hanging from each eye, and a century still to go before it might have offspring. It is a picture that would have been hard to construct without radiocarbon dating, tissue sampling, and the genomic tools of the last two decades.
Deep time, breathing
Human history moves in generations of roughly 25 years. Ten of those generations fit inside a single Greenland shark’s pre-reproductive life. A shark that is only halfway to sexual maturity has already watched, in some abstract fish-brained sense, the entire span from the Wright brothers’ first flight to whatever is happening on the surface of the ocean above it right now.
Similar temporal vertigo has surfaced in other Silicon Canals pieces on how humans measure change against long baselines — from the collapse of upward mobility across two American generations to the 1991 Cambridge coffee-pot camera that accidentally became the first webcam. Human milestones stack up quickly. A single Greenland shark contains dozens of them.
The sharks are still out there, moving at the pace of a slow walk, hearts beating once every twelve seconds. A juvenile born this year will not be old enough to breed until roughly the year 2175. A 400-year-old shark alive today was born around 1625 — a decade before Harvard College was founded. If the current adults survive into the 22nd century, they will do so with hearts full of scar tissue, corneas hosting copepods, and a metabolism so slow that the surface world will feel, to them, as it always has: distant, fast, and largely irrelevant.
Somewhere in the Denmark Strait, right now, an animal that was already swimming when Paul Revere rode is drifting through the dark at the speed of a person walking to the kitchen.
