In the cold darkness of the Arctic deep, Greenland sharks move slowly through water that rarely changes — outlasting dynasties, living through centuries that humans can only read in history books. They may reach 400 years of age, yet almost nothing is known about the biology behind that extraordinary lifespan.
Now, for the first time, scientists have sequenced the complete genome of one of these animals. What they found inside may rewrite how we think about aging.
A genome finally decoded
A team led by Shigeharu Kinoshita, a fisheries chemist at the University of Tokyo, has sequenced 96.7% of the Greenland shark genome. Their findings were published May 19 in the journal PNAS. It marks the first time a near-complete genetic blueprint of Somniosus microcephalus has been assembled — and what it contains surprised even the researchers.
The Greenland shark is the longest-living vertebrate on Earth. Scientists estimate these animals can reach up to 400 years of age, and they don’t reach sexual maturity until around age 150. They inhabit depths of up to 1.65 miles in the North Atlantic and Arctic — conditions that have made them extraordinarily difficult to study. Their biology, until now, remained largely a mystery.
DNA under lock and key: chromatin stability
Among the most striking findings were unique amino acid substitutions in proteins called “linker histones” — proteins that spool and compact DNA, organizing the genetic material inside each cell. The substitutions found in the Greenland shark appear to be unlike those seen in shorter-lived vertebrates.
These changes may stabilize chromatin structure, the tightly packed combination of DNA and proteins that forms chromosomes. Stabilized chromatin could suppress the gradual accumulation of DNA damage that typically builds up over a long life. For a species that lives centuries, that kind of structural protection may be essential — maintaining genomic integrity across countless cycles of cell division and environmental stress is no small feat.
Expanded gene families: immunity, repair, and iron control
The genome also revealed something unexpected in its gene family architecture. Families of genes linked to immune responses and DNA repair pathways were expanded compared to other vertebrates. Kinoshita said this supports the idea that efficient damage repair and immune regulation are central to both longevity and cancer resistance.
A separate finding added yet another layer. The researchers identified a marked expansion of ferritin genes, which govern iron storage and metabolism. Greater ferritin capacity may help the shark limit oxidative stress — a key driver of DNA damage and cancer development — and could also restrict ferroptosis, an iron-dependent form of programmed cell death.
None of this points toward a single “longevity gene.” The picture is more complicated than that. “Extreme longevity is likely governed not by a single gene, but by coordinated changes across multiple biological systems,” Kinoshita said.
What independent researchers say
Outside researchers found the results compelling, though they urged caution about drawing firm conclusions too quickly.
Dorota Skowronska-Krawczyk, a physiologist and biophysicist at the University of California, Irvine, was not involved in the study. She previously showed how DNA-repair-associated genes in the shark’s retina may help preserve its eyesight across a long life. The new findings struck her as plausible — but she noted that direct functional studies will still be needed to confirm the proposed mechanisms.
Aaron MacNeil, a biologist at Dalhousie University in Nova Scotia, said the genomic results support the idea that Greenland sharks are exceptionally long-lived. He expressed skepticism, though, about the 400-year age estimate specifically. That figure comes from radiocarbon traces left by Cold War nuclear bomb testing, detected in the layered lenses of shark eyes. MacNeil’s concern is that slow ocean mixing at depth could delay the arrival of those isotopes, meaning the age estimate may be inflated. His more conservative read: “we do know they’re damn old — 200 years at least.”
What this means for human aging research
Kinoshita and his colleagues suggest the findings could open new directions in research on human aging and age-related disease. The mechanisms identified — enhanced genome stability, immune regulation, iron metabolism control, and oxidative stress resistance — are all relevant to human conditions including cancer and neurodegeneration.
This isn’t the first indication that the Greenland shark’s biology holds broader lessons. Previous research had already suggested the shark’s metabolism stays stable throughout its life, something researchers have linked to its exceptional longevity. The new genome data adds structural depth to that picture, grounding earlier observations in specific genetic architecture.
Scientists are careful, however, to frame these findings as a starting point. Translating genomic observations into medical applications requires extensive functional studies — experiments confirming that these genes actually do what the sequence data suggests. The genome reveals what tools the shark carries. Understanding how it uses them will take considerably more work.
What comes next
The sequencing of this genome is a foundation, not a finish line. Researchers now have a near-complete map to work from, and the next phase will involve testing whether the identified gene variants and expansions function the way the data implies — through functional experiments, comparative studies across other long-lived species, and deeper investigation into how these mechanisms interact.
For human medicine, the most useful insights may come from understanding the coordination between these systems. How genome stability, iron regulation, and immune function work together to resist the damage that accumulates with age is still an open question. If those interactions can be mapped clearly in the shark, they may eventually illuminate pathways that matter for human health too.