Scientists Read the DNA of Jonathan, a 194-Year-Old Tortoise

A research team has sequenced the genome of Jonathan, a 194-year-old Aldabra giant tortoise, and reports that he carries unique gene variants in most aging pathways. The comparison is with two other giant tortoises: one of his own species, Aldabrachelys gigantea, and one Chelonoidis abingdonii.

The authors say they read his genome and his methylome, the chemical marks that sit on DNA, to look for the molecular basis of his longevity. The paper, published Oct. 9, 2026, in Science Advances, describes Jonathan as the world's oldest terrestrial animal.

The methylation half of the work sets that single animal against a different group: four other Aldabras, from a 5-year-old juvenile to older adults. Against those four, the authors report substantial changes in Jonathan's methylation and in his methylation entropy, a measure of disorder. The regions of his methylome with the least disorder sat at gene promoters, the on-switches of genes. They clustered on genes of the mitochondrial electron transport chain, which releases energy inside cells, and on genes that process RNA.

This, the authors say, suggests that accurate copying of those genes may be crucial for long-lived species. They propose a model in which orderly methylation at gene promoters goes together with efficient energy production in mitochondria, efficient RNA processing and efficient genome repair.

Benjamin Vaisvil of Igenbio in Chicago is the paper's first author and Stephen W. Clark of the Kallel Foundation in Nashville its senior author. The author list spans Vanderbilt University, the St. Helena Government, the Technical University of Munich, Harvard Medical School and the University of California, Los Angeles.