Earth is richly supplied with different types of living organisms, including animals, plants, fungi, and bacteria. Various living organisms co-exist in their environments, forming complex, interrelated communities. Living organisms depend on one another for nutrients, shelter, and other benefits. The extinction of any one species can set off a chain reaction that affects many other species, particularly if the loss occurs near the bottom of the food chain. For example, the extinction of a particular insect or plant might seem inconsequential. However, there may be fish or small animals that depend on that resource for foodstuff. The loss can threaten the survival of these creatures, and larger predators that prey upon them. Extinction can have a ripple effect that spreads throughout nature.

In addition to its biological consequences, extinction poses a moral dilemma for humans, the only species capable of saving the others. The presence of humans on the planet has affected all other life forms, particularly plants and animals. Human lifestyles have proven to be incompatible with the survival of some other species. Purposeful efforts have been made to eliminate animals that prey on people, livestock, crops, or pose any threat to human livelihoods. Some wild animals have been decimated by human desire for meat, hides, fur, or other body parts with commercial value. Likewise demand for land, water, timber, and other natural resources has left many wild plants and animals with little to no suitable habitat. Humans have also affected nature by introducing nonnative species to local areas and producing pollutants that have a negative impact on the environment. The combination of these anthropogenic (human-related) effects with natural obstacles that limit survival, such as disease or low birthrates, have proven to be too much for some species to overcome. They have no chance of survival without human help.

As a result, societies have difficult choices to make about the amount of effort and money they are willing to spend to keep imperiled species from becoming extinct. Will people accept limits on their property rights, recreational activities, and means of livelihood to save a plant or animal? Should saving such popular species as whales and dolphins take priority over saving obscure, annoying, or feared species? Is it the responsibility of humans to save every kind of life form from disappearing, or is extinction an inevitable part of nature, in which the strong survive and the weak perish? These are some of the difficult questions that people face as they ponder the fate of other species living on this planet.