Worldwide it is estimated that the number of vertebrate animals—from zebrafish to non-human primates—ranges from the tens of millions to more than 100 million used annually.[2] Invertebrates, mice, rats, birds, fish, frogs, and animals not yet weaned are not included in the figures in the United States; one estimate of mice and rats used in the US alone in 2001 was 80 million.[3][4] Most animals are euthanized after being used in an experiment.[5] Sources of laboratory animals vary between countries and species; most animals are purpose-bred, while others are caught in the wild or supplied by dealers who obtain them from auctions and pounds.[6][7][8]
Supporters of the use of animals in experiments, such as the British Royal Society, argue that virtually every medical achievement in the 20th century relied on the use of animals in some way,[9] with the Institute for Laboratory Animal Research of the U.S. National Academy of Sciencesarguing that even sophisticated computers are unable to model interactions between molecules, cells, tissues, organs, organisms, and the environment, making animal research