Many opponents of animal experimentation argue that not only is modern medicine not the only cause for the decline in mortality, many medical advances that did contribute to human health were not the result of animal experimentation. Defenders of research have claimed that since there is a strong correlation between the practice of animal experimentation and medical advancement, the former caused the latter. Opponents of research reject this inference. After all, we have independent reasons to expect these phenomena to be correlated. Since the law prescribes that all new drugs, prosthetic devices, and surgical techniques be tried on animals before they are used in humans, we will subsequently find that all medical advances are correlated with prior experimentation on animals. Consequently, the correlation between animal experimentation and medical discovery is the result of legal necessity, not evidence that animal experimentation led to medical advances. Moreover, several influential physicians have offered historical evidence that animal experimentation has not been as responsible for biomedical discovery as defenders suggest. They claim that clinical discoveries played a more substantial role than animal researchers have led us to believe.