On giant tortoise longevity

The Galápagos giant tortoise lives on isolated islands near the equator, where the environment has been stable for a long time. With few predators and less pressure to adapt to major environmental change, evolution has favored long life over flexibility

Humans followed a different path. Over millions of years, our ancestors moved into new environments, changed how they lived, changed their diets, and developed larger brains, language, and tools. This meant humans faced stronger evolutionary pressure to adapt

One possible contributor to this adaptability is retrotransposons. These ancient virus-like sequences found in our DNA copy themselves to new places in the genome, which can change how genes are controlled. This has helped drive evolution and adaptation. But it comes at a cost. When retrotransposons become active at the wrong time, they may contribute to disease, including neurodegeneration, rare developmental disorders, and cancer

Retrotransposons and other transposable elements make up about 45% of the human genome. LINE-1 is the only type of retrotransposon that can still copy itself, and sometimes other DNA sequences, to new places in the genome. Humans have about 500,000 LINE-1 copies, although only about 80 to 100 are functional - the rest have been inactivated by mutations. Giant tortoises also once had active retrotransposons, but all of their copies have been inactive for tens of millions of years. This may be one reason for their unusually long lifespan, and they are not the only long-lived species that shows this pattern