Jonathan the tortoise is 194, and his mitochondrial genes appear to have barely aged
Jonathan the tortoise is 194, and his mitochondrial genes appear to have barely aged
Scientists have mapped the epigenome of Jonathan, an Aldabra giant tortoise living on Saint Helena and the world's oldest land animal, for the first time. The epigenome is the pattern of chemical marks on DNA that determines which genes are switched on or off. The study, published on October 7 in Science Advances, identified 287 unique variants in Jonathan's aging-related genes. Its main finding was that, after almost two centuries, the switches controlling his mitochondrial and RNA-processing genes remained as well regulated as those of a five-year-old juvenile.
Jonathan was already an adult when he was given to a future governor in 1882, so his actual age exceeds his official age of 194. His life overlapped with those of Charles Darwin and Queen Victoria. In April 2026, social media posts falsely announced his death in his veterinarian's name. The maximum lifespan of an Aldabra giant tortoise is about 94 years; Jonathan has lived more than twice that long.
Taking blood from Jonathan was prohibited because of the risk of infection to this much-loved animal, so researchers collected DNA using cheek swabs. They sampled four other Aldabra giant tortoises for comparison and assembled the species' genome using blood from 36-year-old Tank. They identified 287 unique variants absent from both Tank and Lonesome George, the last surviving member of his species in the Galápagos, who died in 2012. These newly identified variants involve DNA repair and telomeres, the protective ends of chromosomes.
With age, DNA methylation, the chemical marking that acts as a set of gene switches, becomes more disordered. Jonathan showed this increasing disorder across his genome. Yet at 272 of the nearly three thousand switches examined, many associated with mitochondrial and RNA-processing genes, his methylation patterns remained as well regulated as those of a five-year-old juvenile. In two other tortoises that reached adulthood in 1969, these switches had become disordered.
A similar link between cellular repair and longevity has been found in comparisons across species: reptiles, amphibians, and fish whose risk of death barely increases with age live, on average, nine times longer than their body size would predict, thanks to enhanced systems for repairing cellular damage. Jonathan now provides a molecular picture of this mechanism. The authors propose that well-functioning mitochondria supply energy for DNA repair, which in turn keeps the switches controlling mitochondrial and RNA-processing genes in order, completing a cycle. RNA analysis requires blood, and taking blood from Jonathan is prohibited. Stable mitochondria may help him live longer, or his longevity may help keep them functioning well. The coauthors include Steve Horvath, who developed epigenetic clocks for measuring aging. A similar pattern has also been found in a human: Maria Branyas, who was the world's oldest living person when she died in 2024 at 117, had substantially more efficient mitochondria than others her age.
Stephen Clark, a coauthor of the study and founder of the Kallel Foundation, told The Guardian:
We are still trying to understand how aging works, and Jonathan gives us a chance to see what happens over a very long period. His mitochondria must be particularly stable, and that offers a clue to longevity more broadly.
The authors next want to test whether artificially stabilizing this type of epigenome can extend life in other animals. Clark described their ultimate goal in a comment quoted by PopSci:
Our goal is to turn these evolutionary clues directly into practical, affordable treatments for ordinary people. Aging is the main risk factor for almost every chronic disease, and the generosity of our donors allows us to make longevity medicine accessible to everyone.