Scientists Took a Cheek Swab From the World’s Oldest Tortoise. His DNA Could Reveal Hints to Longevity
Jonathan, an Aldabra giant tortoise, is about 194 years old and the oldest land animal alive today. Discoveries about his genetics could provide clues to extending lifespan in humans
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Throughout world wars, pandemics and the turn of centuries, there was Jonathan. As the world around him shifted and changed, he lived the slow life munching grass on Saint Helena, a British island territory some 1,200 miles off the western coast of Africa.
The Aldabra giant tortoise is the oldest turtle in recorded history and the world’s oldest living land animal. Caretakers don’t know his exact age, but a photograph from 1882 shows the tortoise looking fully grown, which, for his species, is at least 50 years old. This means that Jonathan would be about 194 today.
“To be honest, I suspect he’s older,” veterinarian Joe Hollins, who looks after Jonathan, told the Washington Post’s Cathy Free in 2022. “But we can never know.”
No matter Jonathan’s exact age, one thing seems certain: Something has made him exceptional when it comes to withstanding the test of time. He has already lived more than a century beyond his species’ 80-year average life expectancy—a feat that his safe environment, diet and medical care alone might not be able to explain.
In a new study published on Wednesday in Science Advances, researchers examined Jonathan’s DNA for genetic clues to his extraordinary age. To collect the data, Hollins propped Jonathan’s mouth open with a gloved finger and swabbed a sample of cheek cells and saliva.
“We almost never get to study an animal this old while it is still alive,” says co-author Steve Horvath, a biologist who studies aging at the University of California, Los Angeles, to the New York Times’ Monique Brouillette.
Key context: False reports of Jonathan’s death
In April, false reports that Jonathan had died were circulated widely, stemming from a fake X post claiming to be the tortoise’s veterinarian. It turned out to be a hoax—a ploy for cryptocurrency donations.
The research team sequenced Jonathan’s DNA and identified 287 genetic variants that were unique to him. Many of these had to do with repairing damage to DNA, reducing inflammation and managing insulin. They also found that he shared aging-related genes with species including naked mole-rats, which almost never get cancer.
Additionally, they looked at Jonathan’s epigenome, the chemical tags on DNA that turn certain genes on and off. As organisms age, these switches become less predictable—tags might inconsistently attach or fall off, leading to erratic activity from genes. The team compared Jonathan’s epigenome with those of four younger tortoises.
Overall, Jonathan showed the chaos, or entropy, in the epigenome that would be expected for his age. But in the areas of the genome linked to things like DNA repair and mitochondria, the energy-producing centers in cells, Jonathan’s chemical tags were especially youthful. At these spots, Jonathan’s epigenome looked similar to DNA from a 5-year-old juvenile tortoise that the researchers studied.
The work doesn’t prove that these markers are the reason for Jonathan’s long life, but they offer a clue to how DNA might endure for long periods. They also align with findings from supercentenarians, humans who have lived to be more than 110 years old.
“Aging is the greatest risk factor for nearly every chronic disease we face,” study co-author Stephen Clark, founder and chief scientist at the nonprofit Kallel Foundation for aging research, says in a statement. “Our goal is to take these evolutionary insights and immediately translate them into practical, affordable treatments for everyday people.”
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But before any of this information can find a medical use, scientists will have to conduct deeper research. For one, Jonathan’s cheek swab contained incomplete DNA, so the team combined his genome with a younger tortoise’s DNA, resulting in a code that was only about 95 percent Jonathan—and allowing for the possibility that some of his unique DNA variants were not included in the sample. A blood test would have produced a full genome, but because of the risk of infection for the tortoise, Saint Helena officials did not allow it.
What’s more, Jonathan is just one study subject, and it’s difficult to generalize any results based on a lone individual. His genome was also compared against only a small handful of other tortoises, as bioinformatics researcher Kousuke Hashimoto of the University of Osaka, Japan, tells New Scientist’s James Woodford, inviting the possibility that the other tortoises also had unique variants that were not identified. Nevertheless, he calls the study “fascinating.”
“The results integrate very well in the wider puzzle of what longevity is,” Björn Schumacher, who studies aging at the University of Cologne in Germany and was not involved in the study, tells the New York Times.
Jonathan was born in the Seychelles, an island nation in the Western Indian Ocean. But as a gift to the governor, he was brought to Saint Helena in 1882, when he was photographed as an adult. Since then, he has been living at Plantation House, the governor’s home, with other giant tortoises.
Hollins took charge of Jonathan’s care in 2009, when the animal was around 180 years old and not in great shape. Among markers of age, such as cataracts and a loss of smell that prevented him from finding his own food, the tortoise suffered from a soft beak that made it hard to graze. The veterinarian hand-fed Jonathan, who recovered and developed a razor-sharp edge to his beak within the next couple of years.
“He is symbolic of resilience, longevity, endurance,” Hollins tells Reuters’ Marta Serafinko, “a persistent presence throughout huge historic events.”