Animals give us inadequate or erroneous information about human disease & toxicology. If you flipped a coin to guess how a human will respond to a drug or chemical, your prediction would be as accurate as testing it on a nonhuman animal. While we are similar on the gross anatomical level, we differ at the cellular and molecular levels where disease occurs and medications act.
Even in a species whose DNA is nearly identical to humans, the chimpanzee, vast differences render them unnecessary models to study human health and disease. Now consider mice, who share even less DNA with humans yet are used in research by the millions. According to Dr. Richard Klausner, former Director of the National Cancer Institute, "We have cured cancer in mice for decades and it simply didn’t work in humans."
“The reason we use animal tests is because we have a comfort level with the process… not because it gives us any real new information we need to make decisions,” said Melvin E. Anderson, director of the division of computational systems biology at the Hamner Institutes for Health Sciences. www.neavs.org
Very important. Without it we wouldn't have all the knowledge we currently have. Of course we need to search for alternative ways other than using animals. I remember back when I found out I was pregnant the rabbit died. No really it died! They used to inject a woman's urine into the rabbit and if it died in 3 days, you were pregnant. Now they have better and more sure ways of telling that don't involve killing a rabbit. Back then it was the surest test they had.