Animal testing or animal research is the use of non-human animals in scientific experimentation. It is estimated that 50 to 100 million vertebrate animals worldwide — from zebrafish to non-human primates — are used annually. Although much larger numbers of invertebrates are used and the use of flies and worms as model organisms is very important, experiments on invertebrates are largely unregulated and not included in statistics. Most animals are euthanized after being used in an experiment. Sources of laboratory animals vary between countries and species; while most animals are purpose-bred, others may be caught in the wild or supplied by dealers who obtain them from auctions and pounds. The research is conducted inside universities, medical schools, pharmaceutical companies, farms, defense establishments, and commercial facilities that provide animal-testing services to industry. It includes pure research such as genetics, developmental biology, behavioural studies, as well as applied research such as biomedical research, xenotransplantation, drug testing and toxicology tests, including cosmetics testing. Animals are also used for education, breeding, and defense research. The topic is highly controversial. Supporters of the practice, 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, with the Institute for Laboratory Animal Research of the U.S. National Academy of Sciences arguing