Jonathan, the giant tortoise, is 198 years old. Here is his secret

Jonathan is an Aldabra giant tortoise who lives at the residence of the governor of St Helena. He is 194 years old, the oldest living land animal on Earth today: the upper limit of the life expectancy for Aldabra tortoises is 93.68 years, making him some 100 years older than the typical upper lifespan limit for his species.

The longevity of Jonathan, who was likely a contemporary of Charles Darwin and Queen Victoria, has confounded scientists: but now the enigma may have been partly unravelled in a study published in Science Advances. It isn’t just “good genes” but his “epigenome” (chemicals and proteins that turn genes on or off), that keeps Jonathan youthful, scientists found.

Researchers analysed Jonathan’s genome and his epigenome to understand his extraordinary longevity: and they found as many as 287 unique gene variants, which control DNA damage-repair, reduce inflammation, regulate insulin, and suppress cancer, thereby reducing the process of ageing.

This is not for the first time that long-lived species have been studied through comparative genomic analysis: the naked mole rat, the bowhead whale, Brandt’s bat and immortal jellyfish being a few examples. These studies have offered important insights into genes markers that slow ageing or curb cancer in these species.

This study, the first of its kind, was led by scientists who study longevity at the non-profit Kallel in the US. “Nature has already solved the puzzle of ageing in remarkable ways, and Jonathan’s genome provides a blueprint for cellular resilience,” said Stephen Clark, founder of Kallel and senior author of the study, in a release.

From Jonathan’s genome, scientists found ‘positively selected genes’ (genes that have, over time, accumulated advantageous mutations) involved in DNA repair and insulin regulation. A further investigation found genes involved in development, metabolism, and immunity. Another study indicated a substantially low resting heart rate of 21 beats per minute.

Aldabra tortoises are believed to have dispersed out of Africa, first from the eastern African coast to Madagascar, then to Granitic Seychelles, and lastly to the Aldabra atoll, located in the Indian Ocean. Today, the Aldabra atoll, a UNESCO World Heritage Site, is home to around 1,00,000 tortoises.

Dr. Clark added that their goal was to take these evolutionary insights and translate them into “practical, affordable treatments for everyday people.”

While humans live for about 80 years (and rare individuals 100 years), there are some animals, plants and fungi that can live for several hundred or even several thousand years, and often show negligible senescence (biological process of growing older), said a 2014 study published in Ageing Research Reviews. “The longest living animals are also among the simplest ones,” said the paper, citing corals, jellyfish, comb jellies, hydras, and sea anemones, which “can become in some cases potentially immortal.”

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