Giant tortoises are characteristic reptiles of certain tropical islands. They occur (some species are now extinct) in such places as Madagascar, the Seychelles, Mauritius, Réunion, the Galápagos Islands, Sulawesi, Timor, Flores and Java, often reaching enormous size — they can weigh as much as 300 kg (660 lbs) and can grow to be 1.3 m (4 ft) long. However, giant tortoises also once lived on the mainland of Asia and Australia, as follows from fossil finds in the Shivalik Hills in India. Today, the world's largest population inhabits Aldabra Atoll in Seychelles, where there are approximately 100,000 individuals.
These animals belong to the most ancient group of reptiles, appearing about 250 million years ago. In the Upper Cretaceous, 70 or 80 million years ago some already became gigantic and about 1 million years ago these reptiles reached the Galápagos Islands. Until 100,000 years ago most of the gigantic species began to disappear for unknown causes and only 250 years ago there were at least 20 species and subspecies in islands of the Indian Ocean and 14 or 15 species in the Galapagos Islands. From those, only one of the species of the Indian Ocean survives in the wild, the Aldabra Giant Tortoise (two more are claimed to exist in captive or re-released populations, but some genetic studies have cast doubt on the validity of these as separate species) and 11 in Galápagos.
They are one of the world's longest-living animals, with an average lifespan of 100 years or more. Harriet the Turtle, (Charles Darwin's turtle) as reported by the Australia Zoo was 175 years old.