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  • Animal tests can be very unreliable.

    It should be obvious to everyone that animals are very different from humans. They have different genes, different proteins, and different metabolic pathways. Different germs cause diseases, and different substances can cause cancer. The same genetic diseases can cause very different reactions. For these reasons, it is very risky to extrapolate data found in animals and use it for humans.

    In the last section, many cases of the triumph of animal testing were discussed. It is true that animal testing helped to improve science in these instances. However, in many other instances, animal testing hindered medical development. For example, decades ago, patient studies indicated a relationship between tobacco use and cancer. There was very strong evidence supporting this hypothesis, and many scientists held it to be true. However, during experiments using animals, tobacco repeatedly failed to produce cancer in test subjects. Due to these failed trials, warnings about the dangers of cigarettes were put off for many years. The same exact story was repeated when asbestos was linked to cancer, and alcohol linked to cirrhosis of the liver.

    Surgical experiments using dogs have also failed multiple times. When the technology to replace clogged arteries with a patient's own veins was first developed, the procedure failed miserably when tested on dogs. Scientists nearly gave up hope on the process, but it later proved to be successful in humans. Likewise, kidney transplants are quickly rejected when put into healthy dogs. Therefore, many scientists doubted the likelihood of successful transplants of this organ on humans. However, kidneys are much more readily accepted in humans. We now know that this is because kidney failure stifles the immune system response leading to organ rejection.

    Many diseases and substances act differently in humans than they do in animals. Transgenic mice containing the defective gene causing cystic fibrosis do not show the symptoms characteristic of the condition in humans. This makes them useless for studies. Many carcinogens do not act the same way in nonhuman animals. In one study, only 7 of the 19 tested carcinogens produced cancer in animal test subjects. Other tests found only a 70% correlation between known carcinogens and cancer in animal subjects (however, this correlation would be 50% simply by chance). Many drugs have been proven dangerous only after causing serious side effects in human patients. They may have passed the animal toxicity test with flying colors, but once they reached the market, they were deadly. One drug, Fialuridine, caused liver failure in 7 out of 15 patients who used it. Another, Milrinone, increased the mortality rate of patients with heart failure by 30%. During testing, it was shown to decrease this rate.

    And of course, another disadvantage of animal testing is the ethical issue. Many people feel squeemish when thinking about testing being done on animals, such as cats and dogs. It seems cruel that these animals should be caged up and forced to suffer all in the name of science. Still, many assert that the end justifies the means. Do humans have the right to use and exploit animals simply for their own benefit? This is a question that may never be resolved.

    site created by Catherine Militello, 2004.