Fossil records show that several thousand plants and animals have disappeared during the last 10 million years. Extinction results either from natural disasters, climatic changes, or unsuccessful competition for resources with other species. Over the course of earth's history, the average species survives for 5-10 million years, then disappears. Nevertheless, life continues to flourish because most parent species leave behind at least one lineage equipped to exist in a changing world. Natural extinction of ancestral species is a normal occurrence followed by the evolution of daughter species which quickly adapt and claim available niches.

Today's conservative rate of extinction is one species per day. The most familiar mass extinction ended 65 million years ago when the last dinosaur perished. During that period, one species disappeared every one to ten thousand years. Why is the rate so accelerated now? As our human population increases, more land is cleared for agriculture, livestock, timber, and development while resources are degraded and consumed faster than nature can replenish them.