Scientific Critique

FACTSHEET

Proponents of vivisection argue that animal experimentation advances human medicine. This is the main argument used to justify animal experimentation and to convince the public that vivisection is necessary. In fact, using animals to investigate human diseases is the least defensible of all types of animal research.

Species Differences

Modern evolutionary theory holds that new species develop in response to changes in the environment. Dolphins, once land mammals, now live under water. On the Galapagos Islands, fourteen different species of finches, called Darwin’s finches, evolved, all almost identical in appearance, except that each one has a different size and shape of beak designed to eat a particular type of food. One species has a strong, thick beak for cracking nuts and seeds, while another has a narrow, fine beak perfect for feeding on insects. Each and every species on the planet is a unique combination of structure (anatomy), function (physiology), biochemical, and behavioral patterns that allows it to occupy a special niche in the environment. No two species are exactly alike.

Humans, other primates, and guinea pigs must eat foods containing vitamin C or they will get a disease called rickets. Most other mammals don’t have to eat vitamin C-rich foods because they can manufacture vitamin C in their bodies. It is likely that they evolved the ability to do this because foods in their environment are low in this vitamin. Similarly, humans and cats differ in how they obtain vitamin A. Human bodies contain enzymes that allow them to synthesize vitamin A — necessary to prevent blindness — by converting carotene from certain plants, like carrots, into the vitamin. Cats no longer have the enzymes needed to make vitamin A in their bodies because they evolved to eat meat, and obtain vitamin A from the liver of their prey. If cat food does not contain liver, or if vitamin A is not added to cat food, cats will die.

Differences between species extend far beyond nutrition. Drugs can have completely different reactions in animals and people. Morphine sedates humans, but stimulates cats. Aspirin causes birth defects in rats and mice, poisons cats, and has no effect on horses. The common drugs paracetamol / acetaminophen (Tylenol) and ibuprofen (Advil, Motrin), are toxic to cats and dogs. Penicillin kills guinea pigs and hamsters. Benzene causes leukemia in humans, but not in any laboratory animals. Insulin, epinephrine, and certain antibiotics produce deformities in some laboratory animals.

Many drugs tested safe on animals, but they caused illness and death in humans. The anti-hepatitis drug FIAU, for example, tested safe on various mammals, including primates, but 4 out of 20 human patients who took the drug died from liver damage. Most recently, the FDA-approved anti-inflammatory Vioxx was taken off the market after it caused fatal heart disease in humans.

A 1990 General Accounting Office review of the risks of approved drugs revealed that more than 50% of drugs approved by the U.S. Food and Drug Administration (FDA) posed serious risks to humans, shown by label changes or withdrawal from the market. According to some studies, up to 80% of drugs failed human trials after passing animal tests (Molecules and Markets: A Survey of Pharmaceuticals, The Economist, Feb. 7, 1987, pp. 1-14).

Animal tests can also screen out useful drugs, such as the injectable contraceptive Depo-Provera. The FDA banned this drug in the U.S. around 1973 because it caused cancer in dogs and baboons. Twenty years later, the FDA removed the ban after two decades of experience in countries that permitted its use showed no evidence that it caused cancer in humans.

Despite the fact that animal tests have repeatedly been shown to be unreliable, companies still use them to protect themselves against law suits, while ignoring the results of more accurate non-animal tests, such as cell, bacterial, and tissue cultures. The Ames bacterial culture showed that the flame-retardant TRIS caused cancer, but because TRIS had not produced cancer in animal tests, it received FDA approval and was used in children’s sleepwear for years before being taken off the market.

Many discoveries important to human health have been made without the use of animals. Penicillin, human blood types, hormonal treatments for prostate and breast cancer, the development of anesthetics and x-rays, understanding of the need for certain vitamins, and the isolation of the AIDS virus are just a few of the many advances achieved without animal tests.

Researchers claim that tests on animals are essential in order to see the effect of a drug or treatment on a whole system, on all its cells and organs. As explained above, the biological systems of different species are different, and each system, human or non-human, is made up of many subsystems (respiratory, neurological, and circulatory) that are constantly interacting. Therefore it follows that the effect of a particular substance on the liver of a dog, for example, cannot predict its effect on the liver of a human. Yet diseases animals would never get in nature are artificially induced in them, and then the animals are given drugs in the expectation that the results can be extrapolated to humans. It should come as no surprise that the drugs do not have the same affect on the human as in the animal. Animal models of human diseases are bad science. 

Artifacts of the Experimental Process

In an attempt to compensate for species differences, experiments are often artificially manipulated to an extent that makes interpreting the results impossible. For example, since rodents can be less sensitive to cancer-causing substances than humans, scientists administer much higher doses of these substances to rodents than would be given to humans. Such high doses can kill cells which, at a lower dose, would have become cancerous.

If the rodents do get cancer, was it caused by the high dose, or by the substance itself? If the rodents don’t get cancer, was it because the high dose killed the cells, masking the cancer-causing properties of the substance tested? Would a low dose of the same substance, given to a human instead of to a particular animal species, produce cancer or not? Results based on animal models simply cannot be reliably extrapolated to humans.

The problem of artificially manipulating animal tests to compensate for species differences is not limited to toxicology research. The animal model used to study Parkinson’s disease provides an example. In nature, monkeys do not get Parkinson’s. To create an animal model of this disease, scientists inject monkeys with a toxic compound called MPTP, which destroys the dopamine-producing cells in their brain (sufferers of Parkinson’s have low dopamine levels). Scientists then compare these drugged monkeys to human sufferers of Parkinson’s.

The differences between the MPTP-drugged monkeys and human sufferers of Parkinson’s are great. Human Parkinson’s patients have low levels of certain brain chemicals besides dopamine, such as serotonin, while the serotonin levels of monkeys given MPTP are normal. Also, while the condition of Parkinson’s patients typically deteriorates over time, monkeys given MPTP often improve as soon as the toxic MPTP leaves their body. The cause and course of the disease is completely different in humans and animals. Results produced by the monkey model of Parkinson’s cannot predict results in humans.

The stress of being in a laboratory is yet another significant factor that can distort the findings of tests on animals. Stress affects many physiological processes, such as increasing the production of the hormone cortisone, which raises blood sugar levels and leaches calcium from the bones into the blood stream. Stress also suppresses the immune system, leaving the animal vulnerable to infections and cancer. Besides contributing to animal suffering, laboratory stress is another compounding factor that undermines the relevance of experiments on animals.

Animals and humans are alike in that both are intelligent, sentient beings, deserving of a life lived in freedom and dignity, free from oppression, in habitat that is natural to each. Animals and humans are also different, just as all species are unique. They differ biologically, anatomically, physiologically, neurologically, and behaviorally, so that attempts to apply the results of experiments on one to the other are scientifically invalid.