Jonathan is believed to have been born in 1832. Nearly two centuries later, this giant tortoise is still alive, and his DNA is beginning to reveal clues about his remarkable longevity.
When Jonathan emerged from his egg, the United States was celebrating its 56th year with just 24 states, Charles Darwin was still sailing the seas without knowing he would revolutionize biology, and the future Queen Victoria was only 13 years old.
Jonathan, a giant tortoise living at Plantation House on the island of Saint Helena, photographed on August 21, 2022.
Photo: Kevin Gepford, CC BY-SA 4.0, via Wikimedia Commons.
The animal currently lives on the island of Saint Helena, in the South Atlantic. At around 194 years old, he is considered the oldest known living land animal. His age remains an estimate, but his existence spans several human generations.
How can a tortoise live that long? To better understand this, researchers analyzed Jonathan's DNA and compared it with that of other giant tortoises, which were considerably younger. They did not simply read his genes: they also studied how his body uses them.
The first analysis revealed 287 distinctive genetic variants in Jonathan. Some are involved in mechanisms that contribute to DNA repair, insulin regulation, fighting inflammation, and protection against cancer. These are all important functions for keeping cells in good condition over the years.
Visitors photograph Jonathan, the giant tortoise living at Plantation House on the island of Saint Helena.
Photo: Luke McKernan, CC BY-SA 2.0, via Wikimedia Commons.
DNA also contains small chemical marks that help determine which genes are active. Their distribution generally changes with age. The researchers therefore examined these marks, known as epigenetic marks.
They found another distinctive feature: certain regions of Jonathan's DNA showed an organization that had remained surprisingly stable. These regions include genes involved in the functioning of mitochondria, the small structures that provide energy to cells, as well as in the maintenance of genetic material.
The study suggests that, in some areas, his body has preserved a particularly orderly structure despite the passage of time. This ability could help important mechanisms for cell survival function more effectively.
It is nevertheless impossible to identify a “longevity gene” responsible for his extraordinary age. The study focuses mainly on a single exceptional animal. The differences observed could result from his personal history, his species, or several mechanisms acting together.
By comparing more very old tortoises, researchers hope to determine which characteristics regularly occur in those that live the longest. Jonathan therefore does not yet hold a recipe for extreme old age, but he offers a rare opportunity to study what nearly two centuries can leave in DNA.