12 subspecies of the original 14-15 survive in the wild a 13th subspecies ( C. Specimens of these extinct taxa exist in several museums and also are being subjected to DNA analysis. Tortoise populations on at least three islands have become extinct in historical times due to human activities. The extinction of most giant tortoise lineages is thought to have also been caused by predation by humans or human ancestors, as the tortoises themselves have no natural predators. This decline was caused by overexploitation of the subspecies for meat and oil, habitat clearance for agriculture, and introduction of non-native animals to the islands, such as rats, goats, and pigs. Tortoise numbers declined from over 250,000 in the 16th century to a low of around 15,000 in the 1970s. Charles Darwin's observations of these differences on the second voyage of the Beagle in 1835, contributed to the development of his theory of evolution. On islands with humid highlands, the tortoises are larger, with domed shells and short necks on islands with dry lowlands, the tortoises are smaller, with "saddleback" shells and long necks.
Shell size and shape vary between subspecies and populations. Galápagos tortoises are native to seven of the Galápagos Islands. Spanish explorers, who discovered the islands in the 16th century, named them after the Spanish galápago, meaning "tortoise". For example, a captive individual, Harriet, lived for at least 175 years. Captive Galapagos tortoises can live up to 177 years. With lifespans in the wild of over 100 years, it is one of the longest-lived vertebrates. They are also the largest extant terrestrial ectotherms. It is the largest living species of tortoise, with some modern Galápagos tortoises weighing up to 417 kg (919 lb). The species comprises 15 subspecies (13 extant and 2 extinct). The Galápagos tortoise or Galápagos giant tortoise ( Chelonoidis niger) is a species of very large tortoise in the genus Chelonoidis (which also contains three smaller species from mainland South America).
12 extant subspecies, 2 extinct subspecies
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