Jonathan, the 194-year-old tortoise: what his genes reveal about aging more slowly

When Jonathan hatched, around 1832, there were no electric light bulbs, no telephones and no modern anesthesia. Today, at about 194 years old, this Aldabra giant tortoise is still wandering the gardens of the governor's residence on St Helena, an island in the middle of the South Atlantic. He is considered the oldest known living land animal, and this week he made headlines around the world again.

The reason: a team of scientists analyzed his genome and published a study in Science Advances pointing to a combination of genetic variants and chemical marks on his DNA that may explain, at least in part, how he has weathered the years so well.

A life spanning two centuries

Jonathan arrived on St Helena from the Seychelles in 1882, already an adult, as a gift to the island's governor. A photograph taken between 1882 and 1886 shows him fully grown, which lets experts estimate he was at least 50 at the time. Since then he has outlived dozens of governors, two world wars and the arrival of the internet.

Today he is blind from cataracts and has lost his sense of smell, but his carers say he still has a good appetite and good hearing. His vet hand-feeds him once a week with a diet rich in fruit and vegetables to supplement what he grazes on the lawn.

What they found in his DNA

Jonathan's species, Aldabrachelys gigantea, is long-lived to begin with: many individuals pass 80 or 100 years. But Jonathan goes far beyond that. The researchers compared his genome with those of other tortoises and other animals and found distinctive features in genes linked to several key processes in aging:

• DNA repair: mechanisms that fix the damage that builds up in genetic material over time.
• Telomeres: the "caps" that protect the ends of chromosomes and shorten every time a cell divides.
• Energy and insulin metabolism: pathways that, in many animals, are tied to lifespan.
• Mitochondria: the "power plants" of the cell.
• Cancer prevention: genes that help keep cell growth in check.

Beyond the genetic code itself, the team studied epigenetic marks, small chemical tags on DNA that control which genes are switched on. These marks shift with age and are used as a biological "clock". In Jonathan, that clock seems to tick more slowly than expected.

Why tortoises age so slowly

Turtles and tortoises have fascinated biologists for years. In 2022, a major study in Science analyzed 77 species of reptiles and amphibians and found that many turtles show "negligible" aging: their risk of dying barely rises with age, something very unusual in the animal kingdom. Possible explanations include their protective shells, slow metabolism and continued growth throughout life.

What does this mean for humans?

Caution is needed here. Studying a single exceptional individual has limits: you can't draw general conclusions from one animal. And above all, there is no pill or supplement based on these findings. What this work does offer is a list of biological processes that seem important for aging well, many of which are also studied in people.

Researchers quoted in the science press point out that comparing very long-lived species — tortoises, bowhead whales, naked mole-rats — helps reveal "solutions" that evolution has found several times independently. Those clues may guide medical research in the future.

In the meantime, the science of human longevity keeps pointing to the familiar basics: don't smoke, move every day, sleep well, eat plenty of plants, stay socially connected and keep blood pressure and blood sugar in check.

An island icon

Jonathan appears on St Helena's five-pence coin, receives fan mail from around the world and, in 2022, celebrated his "official" 190th birthday with a cake made of fruit and vegetables. Other giant tortoises live on the island too, including David, Emma and Fred, who share his garden.

His story is also a reminder about conservation: giant tortoises were decimated by sailors who hunted them as a source of fresh meat on long voyages. Today, the Aldabra populations are protected and the atoll is a UNESCO World Heritage Site.

Three facts to impress your friends

• Aldabra giant tortoises can weigh more than 250 kilos.
• They can go long periods without food or water thanks to their slow metabolism.
• Like many turtles, their sex depends on the temperature at which the eggs are incubated.

Jonathan may not hold the recipe for eternal youth, but every day he lives gives us a lesson in patience... and in biology.