They can examine repair pathways.
They can study genes involved in cancer suppression.
They can investigate how extremely long life evolved inside cartilaginous fishes.
The genome provides a map.
Researchers still have to discover which routes matter.
Cancer creates a special problem for long-lived large animals
Every additional year of life provides more time for mutations to accumulate.
Every additional cell provides another place where cancer could begin.
A large animal living for centuries should therefore face an enormous theoretical cancer burden.
Yet species such as whales, elephants, and Greenland sharks exist.
This broader puzzle is often discussed through the idea sometimes called Peto's paradox: cancer rates do not scale simply with body size and lifespan across species.
Long-lived large animals appear to evolve stronger cancer-control mechanisms.
The 2026 Greenland shark genome study found candidate features associated with cancer resistance and DNA maintenance, although much more work is needed to determine their actual effects.
The shark therefore joins whales and elephants as a potentially valuable natural experiment in how evolution solves the problem of keeping many cells alive for a very long time.
The eye may be one of the best places to look for that solution
The retina contains nervous tissue.
Nervous systems are difficult to replace.
Maintaining a functional visual pathway for more than a century requires extraordinary cellular stability.
The 2026 vision study found that Greenland sharks possess an intact rod-based retinal system adapted to dim environments. Importantly, researchers examining old adults found no obvious evidence of the retinal degeneration that would be expected if centuries of life simply produced unchecked damage.
The sharks' bright-light vision appears limited.
Many cone-related genes have become nonfunctional or are not expressed strongly.
That makes sense in a world where daylight may barely reach.
Rod-based vision dominates instead.
Evolution did not preserve visual abilities the animal rarely needed.
It preserved the system useful in Arctic darkness.
Longevity does not mean retaining everything.
It may involve retaining the right things extremely well.
The parasite story becomes stranger after the vision study
The copepod attached to Greenland shark eyes has long fascinated divers and scientists.
The parasite can be large enough to see easily.
It fastens itself to the cornea and can cause visible damage.
For years, photographs of parasite-covered eyes helped create the popular image of Greenland sharks as blind scavengers.
The 2026 study complicates that story.
Corneal parasitism is common, but the shark's visual system remains structurally and genetically functional. Researchers also found that light transmission through the cornea can remain possible despite chronic parasite damage.
This does not mean the parasite has no effect.
An attached copepod can still impair vision.
It means impairment should not be confused with total blindness.
The shark may see far more than people once assumed.
Darkness is not the same as blindness
At several hundred meters in Arctic water, vision operates under conditions humans would consider extremely dark.
A visual system adapted to that world should not be judged by daylight standards.
The Greenland shark's retina is filled with elongated, densely packed rods.
Rods are highly sensitive to low light.
Its visual pigment is also tuned toward wavelengths useful in its environment.
To a human standing on a sunny beach, the shark might appear to inhabit darkness.
To the shark, that darkness can still contain information.
Movement.
Contrast.
Bioluminescence.
Silhouettes.
Nearby animals.
The remaining light may be faint, but evolution has had millions of years to make use of it.
The animal's scientific name hints at its nature
Somniosus is the genus that includes sleeper sharks.
The name fits their slow appearance.
Greenland sharks do not look built for rapid pursuit.
They have thick bodies, small fins relative to their size, blunt heads, and a swimming style that can seem almost effortless.
Yet calling them sleepers can create the wrong image.
These sharks undertake long movements.
A 2024 review of Arctic vertebrate migration described Greenland sharks as highly mobile among Arctic elasmobranchs, capable of journeys beyond 1,000 kilometers and movements between offshore and coastal areas.
They are slow in velocity.
They are not small in range.
Over enough time, patience becomes movement.
Some live deeper than skyscrapers are tall
NOAA records Greenland sharks diving to at least 2,200 meters. More recent scientific literature discusses records approaching 3,000 meters.
At 3,000 meters, sunlight is effectively absent.
Pressure is immense.
Water remains near freezing.
The shark's physiology must function where human beings cannot survive without sophisticated machines.
Yet Greenland sharks can also occur much closer to the surface, particularly in cold northern waters.
This broad depth range means one animal can experience very different physical environments during its life.
Temperature changes.
Pressure changes.
Prey changes.
Light changes.
The shark remains slow, but its ecological world is not simple.
A five-meter shark can hide easily in the Arctic
Size does not guarantee visibility.
A Greenland shark longer than many small boats can disappear into dark water almost immediately.
Its skin is gray, brown, or dark.
Visibility underwater may be poor.
The animal moves quietly.
Much of its habitat is remote.
Sea ice can block access.
Research vessels are expensive.
Longline sampling in Arctic conditions is difficult.
Electronic tags have limited battery lives compared with the shark's lifespan.
A ten-year tracking study would be impressive for a scientist and almost meaningless compared with a four-hundred-year animal.
That mismatch explains why so much remains unknown.
Human research projects are short.
Greenland shark biology is long.
Even our longest studies observe only a small slice of one life
Suppose scientists monitored one shark continuously for twenty years.
That would be a remarkable dataset.
For a 400-year-old animal, it would cover only five percent of its life.
A five-year grant would cover barely more than one percent.
A researcher can spend an entire career studying Greenland sharks without watching one individual pass through a major fraction of adulthood.
This is a central challenge in the science of extreme longevity.
Researchers have to combine different kinds of evidence.
Tagging.
Radiocarbon.
Genetics.
Tissue chemistry.
Historical catch records.
Indigenous and local knowledge.
Stomach contents.
Stable isotopes.
Underwater cameras.
Each method sees only part of the animal.
The complete life may be longer than the institutions studying it.
The shark existed long before anyone knew its age
Greenlandic, Icelandic, and other northern communities had encountered these sharks for centuries.
Fishermen knew their flesh, their large oily livers, their strange appearance, and their slow movement.
Commercial fisheries killed them long before scientists understood the age hidden in their eyes.
The discovery of extreme longevity therefore did not reveal a new animal.
It revealed a new dimension of an old relationship.
People had been hauling centuries-old vertebrates from the sea without knowing how much time each body represented.
That realization changes historical catch numbers.
A shark caught in 1910 might have been born before 1800.
A shark killed in an eighteenth-century fishery might conceivably have been alive before some of the ports harvesting it were established.
Industrial exploitation could therefore remove biological history older than the industry itself.
Greenland shark liver oil once had economic value
The shark's enormous liver contains large quantities of oil.