It is thought that Jonathan, a giant tortoise from the distant island of St Helena, is the longest-lived land-dwelling mammal on Earth. Now, researchers state his DNA could provide clues to slowing down the rate of aging. Now, he may owe his amazing longevity to a combination of genetic characteristics and his ability to maintain key cell systems in a younger condition, a new study indicates. What the researchers discovered, and what it may mean for people.
Who is Jonathan?
Jonathan is an Aldabra giant tortoise estimated to be about 194 years old. In 1882, when he arrived on St Helena in the South Atlantic he was already a full grown animal, probably from the Aldabra Atoll or the Granitic Seychelles, and is now kept in a paddock at Plantation House at the Governor’s residence. People of his kind live longer than 100 years, but Jonathan has well exceeded that.
The best-documented old age
Claims about very old animals are often hard to prove. According to co-lead author Benjamin Vaisvil, other Aldabra tortoises have been said to live as long as Jonathan, but he has the strongest documentary evidence behind his age. Reliable historical records are scarce, many tortoises outlive the researchers studying them, and while a young tortoise’s age can be estimated from growth rings on its shell, adult ages are much harder to pin down.
Inside the new study
The study was published on October 7, 2026 in the journal Science Advances. Jonathan’s genome was sequenced and his epigenome the chemical signals that regulate whether genes are turned on or off in his genome was studied. They analyzed his epigenome and found the epigenomes of four other tortoises from Aldabra, from young to old.
A careful sample
It took time to extract DNA from a nearly 200-year-old tortoise. Since taking the blood from St Helena is restricted due to the potential of infection, researchers took the blood from Jonathan by simulating a feeding and waited for him to bite the air, then carefully opened his mouth with a gloved hand and swabbed under his tongue.
Genes linked to longevity
The team found changes in Jonathan’s genome in pathways tied to longevity, including DNA repair, mitochondrial function, insulin regulation and telomere function. Telomeres are protective caps at the ends of chromosomes, while mitochondria are often described as the powerhouse of the cell.
Unique genetic variants
Researchers identified 287 genes with variants found only in Jonathan, including some connected to tumor suppression and DNA repair. He also carries extra copies of a gene that produces a protein which seeks out aging and cancerous cells.
Parts of him look young
Most of Jonathan’s epigenetic markers look very old. However, in certain regions that act as switches for genes influencing longevity, his level of epigenetic disorder was lower than that of every other tortoise studied except a five-year-old juvenile. In other words, some key systems in his cells appear to be aging more slowly than expected.
Lessons for humans
The findings broadly match patterns seen in studies of exceptionally long-lived people, suggesting that some aging mechanisms may be shared across species. Vaisvil pointed to a recent study of a 117-year-old woman who showed unusually efficient mitochondrial function, echoing results in some of Jonathan’s genetic regions.
The limits of the research
The study has important caveats. Because it involved only one exceptionally old tortoise, it is hard to know whether his traits are unique to him or common among long-lived tortoises, and researchers say they cannot be certain these findings explain his longevity. Environment may also play a role, since Jonathan lives on a tropical island with a diet carefully managed by trained veterinarians.
A gentle giant today
In his younger years, Jonathan was known for overturning chairs and lying on croquet balls, according to his longtime vet and study co-author Joe Hollins. Cataracts have since left him mostly blind. Even so, he still has a big appetite and stretches out his neck when Hollins calls his name. Guinness World Records also gave him “icon” status this year.
