Interest in animals and curiosity about them has inspired art, literature, and religion since before the beginning of history. Thousands of years ago primitive peoples painted pictures of animals on rocky hillsides and on the walls of caves. Legends about animals have been handed down for generations. Many peoples have believed in a spiritual relationship between themselves and certain animals, which they revered as ancestors and guardians. In ancient times, many peoples worshiped gods in animal form, and believed that certain animals were sacred to the gods.

Use of Animals. People have made use of other animals and their products for thousands of years. The flesh, blood, and milk of various animals have provided food. Clothing has been made from hides and fur, and by weaving wool and silk into fabrics. Hides have also served for making tents and other shelters and—processed as leather—countless other useful articles. People use animals for transportation and other work, and as pets. Vaccines, antitoxins, hormones, and various drugs are derived from animal tissues. To better meet human needs, the characteristics of domesticated animals are often modified through controlled breeding.

Certain animals are used in laboratories for scientific research, such as the testing of new drugs. This research, sometimes called vivisection, has brought about many advances in medicine, psychology, and other fields, but has also aroused much opposition on the grounds that it is cruel and unnecessary. In the United States, the Animal Welfare Act (passed in 1966 and amended in 1970 and 1976) and certain Public Health Service guidelines establish standards for the treatment of laboratory animals.

Wild animals—such as lions and leopards in Africa and tigers in Asia—occasionally kill and eat humans. Weasels, wolves, rats, and bears sometimes prey on domestic animals. Plant-eating animals such as rabbits, gophers, and numerous insects destroy crops. Poisonous snakes, spiders, and scorpions, and certain biting and stinging insects, are a source of danger or annoyance in some localities.

The animals most harmful to humans are those that carry or cause disease. Certain mosquitoes spread malaria; in parts of Africa, the tsetse fly spreads trypanosomiasis (sleeping sickness in humans and nagana in domestic animals). Parasitic worms such as hookworms, tapeworms, trichina worms, and various flukes cause serious diseases in many parts of the world.

The domestication and controlled breeding of animals have changed the body structure and habits of many animals. The stocky build of beef cattle and the long, slender legs of race horses are examples of traits developed by controlled animal breeding.

Humans have transported animals from their natural habitats into new localities, often with unexpected results. Mongooses introduced into the West Indies to destroy rats also destroyed many harmless and desirable animals, and themselves became pests. Rabbits and deer introduced into New Zealand by Europeans became pests to agriculture and forestry, since there were no predators to control them.

In addition, humans have destroyed habitats and reduced the range of many animal species by the development of agriculture and industries. In many cases, this destruction has been beneficial to humans. In others, interference with natural conditions has resulted in harm to humans themselves. Recognition of this fact has led to the study of methods of wise conservation of animals and their natural environment.

In spite of various conservation efforts, however, dozens of species of wildlife have vanished from the earth during the past 200 years, mostly as the direct result of human alteration of their habitat or excessive hunting. Examples are the dodo, passenger pigeon, and Steller's sea cow. Hundreds of other animal species are in danger of extinction, and worldwide efforts to save them are underway. Endangered animals include the tiger, Brazilian tapir, giant otter, California condor, whooping crane, and numerous species of whales.