The genetics of extreme longevity
The Galápagos giant tortoise (Chelonoidis niger) possesses a unique biology that effectively pauses the aging process at a cellular level. One famous female tortoise, Harriet, lived to an estimated age of 175, passing away in 2006. Her lifespan is not an anomaly; these reptiles exhibit what is known as negligible senescence, meaning their bodies show minimal decline over time. The reason for this ability lies in their chromosomes. At the end of each chromosome are protective caps called telomeres, which, in humans, shorten with every cell division. This shortening eventually stops cells from dividing and is a primary cause of aging. Galápagos tortoises defy this process. Their telomeres shorten very slowly or not at all, allowing their cells to retain a youthful regenerative capacity throughout their long lives.
In addition to their telomeres, the tortoises have a robust defense against cancer. Large, long-lived animals should theoretically have a higher risk of cancer simply because they have more cells dividing over a longer period. Yet, Galápagos tortoises rarely develop tumors. Genomic studies reveal they have extra copies of genes associated with tumor suppression. These genes make their cells highly sensitive to stress. If a cell accumulates damage that could lead to cancer, it is much more likely to self-destruct through a process called apoptosis. This efficient system of eliminating potentially cancerous cells before they can form tumors is a major reason for their longevity. Their genomes also show specific variants in genes related to DNA repair and a powerful immune response, with some immune-related genes duplicated up to 12 times compared to mammals.
