Extinction is the disappearance of a species. Extinction usually involves (1) a decrease in population sizes within a species and (2) a decrease in genetic diversity within a species. These two processes are related, since small populations usually have less genetic diversity than large populations.

Extinction usually occurs for a variety of interrelated reasons, and it occurs one species at a time. When a large number of species becomes extinct at the same time, for the same reason, a mass extinction event is said to have occurred. Five mass extinctions have occurred during the history of life and have been important in the pattern of evolutionary history. Many biologists consider that a sixth mass extinction of species is now occurring, largely due to human disturbance of the environment, and that the mass extinction now under way may well prove to be the biggest in the history of life on Earth.

Changes in the environment, whether naturally occurring or caused by human activity, may impair the ability of organisms to reproduce; this will cause populations to decline. A species with a small number of populations is in much greater danger of extinction than a species with larger population number and size. For example, a plant species that is limited to a single locality may become extinct if that locality is disturbed by fire, flood, or human activity. The bush Franklinia alatamaha was discovered by the American botanists John and William Bartram in the 18th century. It was growing in just one location in the mountains of the colony of Georgia, on the plateau adjacent to the Altamaha River. The Bartrams took cuttings from these bushes and planted them in a garden; descendants of these bushes are still alive in gardens throughout the United States and Europe. The wild population has disappeared, perhaps when the forest that contained it was cleared for cultivation, perhaps even by a single farmer. The tree Ginkgo biloba was very nearly extinct in its habitat, the forests of north central China. Buddhist priests planted specimens of this tree in their monasteries. Ginkgo trees are now abundant throughout the world where they have been planted in cities, and more recently on plantations for the production of medicinal compounds. Franklinias and ginkgos survive today largely because a small sample of them was rescued from their very small and vulnerable wild populations. . .

Free term papers are not written to satisfy your specific instructions. You can use our professional writing services to buy a custom written research paper, term paper, or essay on Science at affordable price. CustomTermPapers is the best solution for those who seek help in writing term papers, essays, and research papers related to Science and other relevant topics.