Jonathan the 194-year-old tortoise could help humans live longer
By Jacopo Prisco, CNN
(CNN) — A new genetic analysis has revealed potential clues to the longevity secrets of a giant tortoise named Jonathan, the world’s oldest land animal. Researchers say the findings could eventually inform treatments aimed at slowing age-related cellular decline in humans.
Believed to be 194 years old, Jonathan is an Aldabra giant tortoise — a species native to the islands of Seychelles in the Indian Ocean — and he has spent most of his life on the remote South Atlantic island of St. Helena, a British Overseas Territory.
Giant tortoises are among the longest-lived land animals on Earth, with some records indicating they can regularly survive for more than a century. But Jonathan, approaching his 200th birthday, is an extreme example in this already special group.
One explanation for these animals’ extended lifespan might be that they take life very slowly — even at the genetic level, according to a new study published Wednesday in the journal Science Advances.
“The assumption has always been that their metabolic rate is very low compared to us,” said study coauthor Justin Gerlach, a fellow in biology at the University of Cambridge in the United Kingdom. “That means that the processes that are going on inside the cells are slower, so there are fewer chemical reactions and therefore less damage to the cells and to the DNA.”
Gerlach and his colleagues tested those assumptions by examining Jonathan’s genome — the complete DNA set — as well as his epigenome, the switches that turn genes on and off. The researchers found 287 gene variants associated with protecting the animal from the inevitable cellular damage that comes with time.
“He does have some genes that are particularly good for DNA repair and reducing inflammation,” said Gerlach, referring to two key mechanisms that are known to slow down aging processes.
More specifically, the analysis suggests that Jonathan can continue expressing the right genes at the right levels even in old age. This process typically starts to break down much earlier in most other animals, including humans, Gerlach said.
“Our cells start doing the wrong things and we get cancers, for example. But Jonathan has still got the genetic controls of a much younger animal,” he added. “We don’t know whether that’s because he is exceptional, or whether actually that’s what giant tortoises do. But it does mean that their bodies are much fitter than we would expect for their age, compared to what would happen with humans.”
Other members of the animal kingdom, including species of whales, sharks and clams, are also known to reach older ages, but scientists know little about the genetic and molecular mechanisms that drive an animal’s lifespan to be long or short, said Joao Pedro de Magalhaes, chair of molecular biogerontology at the UK’s University of Birmingham, who was not involved with the study.
“Understanding why some species live much longer than others would represent a major breakthrough in our understanding of ageing and longevity, with potential applications to human health,” he added via email.
A blueprint for resilience
Jonathan’s exact age is unknown. Scientists have estimated the great reptile is around age 194 based on a photograph from 1882 that depicts him in St. Helena already at adult size. Giant tortoises typically reach this size at about 50 years old, allowing researchers to deduce his current age from a photo taken 144 years ago.
Based on this estimate, St. Helena’s governor in 2022 gave Jonathan an official birthday — December 4, 1832; Abraham Lincoln, Charles Darwin and Queen Victoria would have all been alive then and in their young age.
However, Jonathan could be even older — 200 years old or more, according to Gerlach. The animal’s arrival in St. Helena was likely because the public in the 1800s regarded giant tortoises as “curiosities,” and as such he would have made for an interesting gift for a colonial administrator. This fate spared him from a far more gruesome one that was common for the species at the time. Crews on exploration vessels often captured the giant creatures and kept them as food supplies.
“The ships would collect tortoises from the Seychelles, the Galápagos or Mauritius, and they could keep them on board for months without bothering to feed them or give them water,” Gerlach explained. “They’d still be alive and edible. It was a grim practice that contributed to the extinction of the Mauritian species.”
Weighing about 400 pounds (180 kilograms), Jonathan is still active despite having lost his eyesight to cataracts. He is a popular tourist attraction, and earlier this year he was the subject of a viral April Fools’ Day joke that wrongly claimed he had died, prompting the government of St. Helena to confirm he was still alive and well.
Due to the animal’s old age and to avoid any risk of infection, the study authors collected DNA samples by swabbing his mouth, rather than drawing blood. The team noted that the saliva samples prevented the use of more accurate DNA sequencing techniques.
The researchers compared Jonathan’s DNA and epigenome with that of much younger members of his species found on the Aldabra Atoll of Seychelles and saw remarkable similarities. In addition, his mitochondria, the cell structures that produce energy, were in surprisingly optimal shape.
“We don’t yet know if this is common to his species, but one of our next goals is to analyze other Aldabra tortoises to find out,” said senior study author Dr. Stephen Clark, the founder of Kallel Foundation, a Nashville-based nonprofit dedicated to increasing human longevity.
“There is some data showing that mitochondrial health is important for long-lived species, and it has been shown that human supercentenarians have more efficient mitochondria, so our results in Jonathan fit with these findings,” Clark said in an email, referring to people who reach the age of 110 or more.
Jonathan’s genome offers a map for cellular resilience that could translate into treatments for people, Clark added. “We are very interested in finding generic human drugs that improve mitochondrial health, and we want to bring these drugs into human clinical trials within the next year or two.”
More specimens needed
With a single animal, the new findings cannot tell researchers exactly why Jonathan has lived so long, and more giant tortoises and other long-lived species are needed to get a better picture of genetic drivers of longevity, according to Handan Melike Dönertaş, an assistant professor and genomics researcher at the Middle East Technical University in Turkey. She was not involved with the study.
“By comparing such extreme individuals with others, not only among humans such as centenarians, but also in other species, we can start to learn what makes them special, and with advances in medical technology we may find ways to apply what we learn,” she said in an email.
Jonathan is an ideal research subject for investigating genetic changes that may be linked to longer life, making the new study compelling, said Vincent J. Lynch, a professor in the department of biological sciences at the University at Buffalo in New York.
However, some of the study’s methods are prone to give false negative and false positive results, said Lynch, who was not involved with the work. “We’ve developed computational methods to determine if mutations are adaptive, good or deleterious,” he wrote in an email. “But these methods are very sensitive to assumptions we make about how genes evolve. The model they used, while common, makes unrealistic assumptions that can lead to good mutations being called bad and bad mutations being called good.”
Still, the study is a valuable complement to a growing body of research and further supports that giant tortoises are unique in their ability to defy expectations for lifespan and health, said Ylenia Chiari, an associate professor, faculty of Medicine & Health Sciences, at the University of Nottingham in the UK. Chiari has also studied the longevity of giant tortoise species in the Galápagos but was not involved in the recent work.
“These findings are beginning to unravel the complexity of the mechanisms that allow some organisms to achieve exceptional longevity,” Chiari said in an email. “Ultimately, one of the goals of studying these and other exceptionally long-lived animals is to gain insights that may be transferable to human ageing and cancer research.”
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