Scientists sequence genome of Jonathan, the 194-year-old tortoise, and find clues to his long life

Jonathan, an Aldabra giant tortoise thought to be around 194 years old, has had his genome sequenced for the first time. The study was published Wednesday in Science Advances. Jonathan is described as the world's oldest living land animal, and researchers hope his DNA can tell us something about aging.

Jonathan hatched around 1832 in the Seychelles archipelago. He was already in his twenties when Charles Darwin published On the Origin of Species. In the 1880s, when he was in his fifties, he was brought to the remote island of Saint Helena with three other tortoises, as a gift to the British colonial governor. He has lived there ever since.

Aldabra giant tortoises often live past 100. Jonathan is still a big outlier, even for his species. To find out why, researchers took swabs from his cheeks and compared his genome with those of several other tortoises, including a 36-year-old named Tank.

The study reports that Jonathan has "unique gene variants in most aging pathways." These include DNA repair, insulin regulation, mitochondrial function and "low entropy" methylation. Mitochondria are the parts of a cell that produce energy. Methylation refers to chemical tags on DNA that help control how genes are switched on and off.

Stephen Clark, an aging researcher at the non-profit Kallel Foundation and an author of the study, spoke with 404 Media. "Aging is very complicated, and there's all these different hallmarks," he said. "We're still just at the very beginning of trying to understand aging."

Getting the samples took years. Clark first contacted Jonathan's caretakers in 2017. A blood draw was judged too risky, so Jonathan was coaxed into opening his mouth for a swab. Incomplete early samples, the Covid pandemic and new rules on access to Jonathan caused delays. The samples were finally flown from Saint Helena to Florida by the U.S. Space Force.

Many of the results were what the team expected, based on studies of other long-lived people and animals. Jonathan had variants linked to DNA repair, to the upkeep of telomeres (sequences tied to aging), and to autophagy, the way cells recycle their own parts.

The surprise came in his methylome, the full set of those chemical tags. The part linked to mitochondria was unusually clean, or "low entropy." Most of Jonathan's genome showed disorder in line with his age. But his mitochondrial methylome looked similar to that of a five-year-old tortoise the team also tested.

Clark said the comparison, across 189 years of age difference, has not been done before, even in humans, because no human lives that long. He cautioned that it will take more research to follow up on the lead and to sort out the many genetic factors that shape lifespan.

Clark also said his team at Kallel Labs studies long-lived species to find possible new targets. "The ultimate goal of the company is to affect human healthspan and lifespan," he said.

Jonathan still lives at Plantation House, the governor's residence on Saint Helena. He and his fellow tortoises are a tourist attraction on the island. Saint Helena is also known as the place where Napoleon Bonaparte was exiled and died, about a decade before Jonathan is thought to have hatched.