A Greenland shark is not immortal.
It can be injured.
It can be caught.
It can become diseased.
Eventually it dies.
Longevity in complex animals almost certainly depends on many interacting systems.
The new eye study simply adds another clue.
Whatever allows a Greenland shark to survive for centuries must also allow vital tissues to remain useful for centuries.
Living a long time is not enough.
The animal must keep functioning.
A four-hundred-year lifespan would be biologically pointless if essential organs failed after sixty years.
The preserved retina shows how unusual that maintenance may be.
The genome is beginning to reveal another layer
Only a few months after the eye study, another important paper appeared.
In May 2026, researchers published a chromosome-level genome assembly for the Greenland shark in the Proceedings of the National Academy of Sciences. The assembled genome measured about 5.9 billion base pairs, making it enormous compared with the human genome.
The researchers looked for genetic features that might contribute to extreme lifespan.
They found signals involving several biological systems already associated with longevity, including DNA repair, immune function, and cancer resistance. They also identified unusual changes in a linker histone called H1.0 that might improve chromatin stability and help protect cells from molecular damage.
The authors were appropriately cautious.
These are possible mechanisms.
They are not a final answer.
A genome can identify promising pathways, but proving that one change causes extreme longevity requires much more work.
Still, the study brings scientists closer to a question that naturally follows the age estimate.
How does a vertebrate body remain alive for that long?
Four hundred years means four hundred years of cellular damage
Every living cell faces damage.
DNA breaks.
Proteins fold incorrectly.
Molecules oxidize.
Cellular machinery accumulates errors.
Some cells divide, which introduces opportunities for mutation.
Other cells must remain functional for long periods.
Cancer risk can increase as damaging mutations accumulate.
In humans, aging is associated with failures across many of these systems.
A Greenland shark living several centuries has far more chronological time for damage to occur.
The obvious explanation might be that the shark simply does everything slowly.
Cold water lowers metabolic rates.
Slow metabolism may reduce some kinds of molecular stress.
The animal moves slowly and lives in a cold environment where chemical reactions can proceed more slowly than they do inside a warm mammal.
NOAA describes slow metabolism as one leading explanation for the shark's slow growth, slow movement, and long lifespan.
Yet low metabolism probably cannot explain everything.
Centuries remain centuries.
The 2026 genome and vision studies suggest that active maintenance systems may matter alongside slow living.
The shark may not simply avoid damage.
It may also be unusually good at surviving it.
Cold is part of the story
Greenland sharks inhabit some of the coldest marine environments regularly occupied by a large shark.
The 2026 vision study describes the species living in water as cold as about โ1.1ยฐC and at depths approaching 3,000 meters. NOAA records observations to at least 2,200 meters and notes that the species can tolerate Arctic water year-round.
Cold changes physiology.
Muscle works differently.
Digestion slows.
Nerve conduction changes.
Metabolism falls.
Growth becomes slower.
For an animal adapted to those conditions, a slow pace is not a disability.
It is normal.
This makes the Greenland shark a useful reminder that animal speed should always be judged against environment.
A cheetah would be useless at the bottom of an Arctic fjord.
The shark's world rewards a completely different strategy.
The slowest large predator still catches animals
The Greenland shark has a reputation for sluggish movement.
That reputation is deserved.
Tracking and physiological studies have repeatedly found extremely low swimming speeds compared with many other sharks.
NOAA gives a maximum speed under roughly 2.9 kilometers per hour.
Yet stomach contents tell a puzzling story.
Researchers have found fish, squid, seals, and other large prey associated with Greenland shark diets. The 2026 visual study summarizes the species as an opportunistic predator and scavenger that consumes fish, squid, seals, and large carrion such as whale remains.
A shark that seems too slow to catch a seal sometimes contains seal remains.
That puzzle has produced several hypotheses.
Some seals may be caught while resting.
Some may already be dead or injured.
Greenland sharks may approach in darkness with very little warning.
They may scavenge carcasses more often than observers realize.
Different feeding methods may operate under different conditions.
A 2019 management review notes observations consistent with both scavenging and active predation, while acknowledging that scientists still do not fully understand how such a slow animal captures fast marine mammals.
The shark remains mysterious even after scientists learned its age.
A map of the Greenland shark's world
Imagine the North Atlantic from above.
At the center sits Greenland, surrounded by cold water.
To the west are Baffin Bay, the Canadian Arctic Archipelago, Labrador, and the cold western North Atlantic.
To the east are Iceland, the Norwegian Sea, Svalbard, and the waters leading toward the Arctic Ocean.
The Greenland shark occupies this cold northern world, moving through coastal fjords, continental shelves, deep slopes, and open water.
Research reviews describe its best-known range as the Arctic and North Atlantic, with animals recorded from near the surface into very deep water. Some related observations and rare records extend the known depth range close to 3,000 meters.
Now imagine the map vertically instead of horizontally.
Near the surface, winter ice covers parts of the sea.
Below lie cold coastal shelves.
Then the bottom falls away.
Five hundred meters.
One thousand meters.
Two thousand meters.
The shark can move through a vertical landscape larger than many mountain ranges.
Tagging work indicates that Greenland sharks can also travel more than 1,000 kilometers, and some individuals make repeated movements between coastal and offshore environments.
They are slow swimmers without being stationary animals.
Given enough time, slow movement covers enormous distance.
That statement could describe their entire life history.
Time changes the meaning of speed
Suppose an animal moves slowly but has several centuries in which to move.
A human naturally watches it for minutes or hours and concludes that very little is happening.
The shark's scale is different.
A migration of 1,000 kilometers does not have to be completed at tuna speed.
Growth does not have to be fast if life lasts centuries.
Sexual maturity does not have to arrive at age ten if death from old age may remain centuries away.
The Greenland shark makes many familiar biological rules feel temporary.
Humans are adapted to judge life according to our own lifespan.
We expect childhood to occupy a small fraction of life.
We expect reproduction to begin relatively early.
We expect centuries to contain many generations.
For this shark, a century may still belong largely to development.
That is what makes the maturity estimate so difficult to grasp.
A 150-year childhood is not quite the right description
Popular accounts sometimes say Greenland sharks have a 150-year childhood.
The phrase is memorable, but it is biologically imprecise.
A shark is not behaving like a human child for a century and a half.
It feeds independently and survives as a predator long before sexual maturity.
The important point is reproductive timing.
Females appear to reach sexual maturity at very large body sizes, and the 2016 age model placed that transition at about 156 ยฑ 22 years.
That means a female could survive for more than a century without contributing offspring to the next generation.
From a conservation perspective, that matters much more than the word childhood.
It means every mature female represents an extraordinary investment of time.
Removing one is not comparable with removing an adult from a fast-growing fish population.
A replacement cannot simply mature next season.
One dead shark can represent centuries of biological investment
Imagine a female that reaches reproductive maturity at 150 years.
She is caught at age 160.
Biologically, the population may have lost an animal that spent a century and a half reaching the point at which she could reproduce, only to lose her after a few mature years.