194-Year-Old Tortoise Jonathan Reveals Genetic Secrets to Extreme Longevity

Jonathan arrived at Plantation House on the remote island of St Helena in 1882, already a fully grown Aldabra giant tortoise, likely transported from the Aldabra Atoll or the Granitic Seychelles. Now, at an estimated 194 years old, he holds the distinction of being the world's oldest known land animal—and scientists have begun to understand why his body has resisted the wear that claims most creatures far younger than he is.

Aldabra giant tortoises routinely live past 100 years, but Jonathan has nearly doubled that span. What makes his case scientifically valuable is not merely his age but the documentary trail that supports it. Benjamin Vaisvil, a researcher affiliated with the organisation Kallel and co-lead author of a study published in October 2026 in Science Advances, noted that while other Aldabra tortoises have been claimed to reach Jonathan's years, none carry the weight of historical evidence that Jonathan does. That clarity allowed researchers to sequence his genome and analyze his epigenome—the chemical markers that determine which genes turn on and off—in search of the biological architecture underlying his longevity.

What they found was a constellation of genetic advantages. Jonathan's genome contains 287 genes with variants unique to him, including several linked to tumor suppression and DNA repair. He also carries extra copies of a gene encoding a protein that hunts down aging and cancerous cells. Beyond these raw genetic differences, the researchers discovered something equally striking in his epigenome. Using an analogy Vaisvil offered, the genome is like a cookbook, while the epigenome resembles handwritten notes in the margins. As organisms age, those notes typically become harder to read—a phenomenon called methylation entropy. In most of Jonathan's genome, the notes look very old indeed. But in certain stretches of DNA that act as switches controlling whether genes are turned on or off, Jonathan's methylation entropy was lower than that of every other tortoise studied except a five-year-old juvenile. These were precisely the regions that control genes influencing longevity.

The researchers compared Jonathan's epigenome with those of four other Aldabra tortoises ranging from juveniles to older adults. Obtaining samples required an unconventional approach: while pretending to feed Jonathan, they waited until he began biting the air, then wedged his mouth open with a gloved hand and scraped under his tongue with a specialized kit. St Helena officials restrict blood draws to prevent infection risks. The genetic patterns that emerged—enhanced DNA repair, improved mitochondrial function, better insulin regulation, and more robust telomere function—aligned with what scientists have observed in exceptionally long-lived humans. A recent study of a 117-year-old woman, for instance, found unusually efficient mitochondrial function, echoing findings in certain regions of Jonathan's genome.

Yet the study carries significant limitations. It examined only one exceptionally old tortoise, making it impossible to determine whether the traits identified are unique to Jonathan or common among long-lived members of his species. Vaisvil was candid about this constraint: "We cannot say for certain that what we found is the reason for his longevity." Environmental factors almost certainly played a role. Jonathan has lived on a tropical island with an optimal diet carefully managed by trained veterinarians—conditions most wild tortoises never experience.

Joe Hollins, Jonathan's longtime veterinarian and a co-author of the study, has watched the tortoise age across decades. When younger, Jonathan was known for mischievous antics: overturning chairs, lying on croquet balls. Cataracts have since left him mostly blind. Hollins describes him now as "a gentle giant." Despite his age, Jonathan retains a voracious appetite, lifting his head and stretching his long neck when Hollins calls his name. The veterinarian knows the tortoise recognizes him not out of affection but in anticipation of food—and he has made peace with that transactional relationship. "I have a huge affection for him," Hollins said.

Jonathan has become more than a biological specimen. He has lived through world wars and the rise and fall of empires, a persistent presence on an island where few things endure. Guinness World Records granted him "icon" status in 2026. Hollins sees in him a symbol of resilience and longevity, a creature whose mere existence speaks to endurance across historic upheaval. The genetic secrets he carries may illuminate pathways to longer human life—or they may prove to be Jonathan's alone, a singular arrangement of molecules that allowed one tortoise to outlive nearly everyone who has ever studied him.