Extinction

A species is extinct when no living members are left anywhere. It is endangered when it is at risk of extinction. Extinction happens when the environment changes faster than a species can cope: a new predator or disease arrives, its habitat is destroyed, the climate changes, or it is hunted.

Extinct	When	Why
Dodo	1600s	Sailors reached Mauritius; hunting, and the pigs, rats and monkeys they brought ate its eggs. It had never had predators
Woolly mammoth	Most about 10,000 years ago; the last, on Wrangel Island, about 4,000 years ago	A warming climate shrank its cold grassland, and humans hunted it
Passenger pigeon	1914	Once billions in North America; hunted for food and its forests cut down
Thylacine	1936	Hunted in Tasmania; the last one died in Hobart Zoo

Biodiversity is the variety of living things in a place, or on Earth. It matters because living things depend on each other in food webs, and because variety is what lets life cope with change. A species with lots of variation is more likely to have some individuals that suit new conditions. A species of copies has all its eggs in one basket.

Gene banks store hereditary material so that a species’ genes are not lost. Seed banks keep seeds cold (about −18 °C), dry and sealed, so they stay alive for decades. The Svalbard Global Seed Vault in Arctic Norway is built into a frozen mountain and holds more than a million samples from around the world; Kew’s Millennium Seed Bank in Sussex is the biggest store of wild-plant seeds. Frozen zoos keep eggs, sperm and cells from endangered animals. Breeding programmes in zoos raise numbers and keep variation. Gene banks keep samples from many plants of a species, not one, to preserve its variation.

Fossils. A fossil is the remains or traces of a living thing from long ago, preserved in rock: bones, shells, leaves, footprints. Fossils show that many species that once lived are now extinct, and that living things have changed over millions of years. In the early 1800s Mary Anning found the skeletons of extinct sea reptiles, ichthyosaurs and plesiosaurs, in the cliffs at Lyme Regis in Dorset.

Stretch Frozen is not saved: a species also needs a habitat to live in, so protecting habitats and setting up reserves comes first. Scientists have talked about bringing back extinct species such as the mammoth from frozen DNA, but nothing extinct has been brought back to live in the wild, and most scientists say protecting living species matters more.