Scientists often site the structural and physiological similarities between animals and humans as the rationale for animal experimentation. They believe that because we share similar biological processes, data obtained from animal models can be extrapolated and applied to human conditions. Although this methodology has become the norm in research labs around the world, a closer look at the data makes it clear that species who share close evolutionary relationships or anatomical similarities do not necessarily undergo the same biochemical mechanisms or physiological responses. In fact, it can be dangerous to apply animal-derived data to humans.
Because evolution, molecular biology, and genetics show that animals and humans differ in profoundly important ways, animal models will never be able to accurately recapitulate what happens in the human condition. People, in general, have longer life expectancies than most nonhuman species, metabolize substances differently, and are exposed to a multitude of different environmental factors over our lifetimes. Diseases that develop in people differ in significant ways from artificially imposed symptoms or in animals that have been genetically engineered. The claim that animals can accurately predict human response is false, as today we know that miniscule differences in genes and their regulatory mechanisms within the human species make it difficult to foresee drug response in different people. When you need medical treatment, you want what works for you, not what works in a completely different species.
Even scientists are aware of the inherent flaws that come with using animals as models of human disease. They recognize that no one model can recapitulate the human condition. Although they have discovered some animal models which appear to mimic parts of what occurs in humans, and conclude they have a “good” model, the truth is, this so-called recapitulation of the human condition may arise by very different mechanisms in animals due to the intrinsic differences between species. There is very little consensus among researchers about what the “right” animal model to use is in many instances, because in reality, there is no such thing.
Drugs that may be effective in animals may not be safe or effective in humans (and vice versa), and there are many examples where reliance on animal models has proven to be misleading and detrimental to human health. Probably the best-known example is thalidomide, used in the 1950s as a sedative and prescribed to treat morning sickness in pregnant women. Thalidomide was safe when tested in animals, but when used by mothers-to-be, led to birth defects in over 10,000 children.
Another example is the widely used antibiotic, penicillin. Animal testing showed that penicillin was ineffective at treating infected rabbits (and was actually toxic to guinea pigs), yet later it proved safe and effective for treating bacterial infections in most humans. Even data collected from experiments on aspirin could not be accurately extrapolated from animal studies to humans, as it causes birth defects in mice and rats, but is harmless to the human embryo. Had we relied on animal testing as it is conducted today, we would have rejected aspirin based on its potential to induce adverse effects in animals. In fact, it has proven to be widely beneficial for multiple uses including: pain management, preventing strokes due to blood clots, and even cancer prevention.
Even model systems with more phylogenetic similarity to humans, like primate models, fail to predict what happens in humans. One of the best examples of this occurred when monkeys treated with a therapeutic antibody (anti-CD28 monoclonal antibody TGN1412) did not predict the potentially fatal immune response that was triggered in humans. These are just a few examples that demonstrate the dangers of applying data obtained in one species to another.
Whether discussing HIV/AIDS, cancer, heart disease, diabetes, drug testing, or virtually any other area of investigation, there are numerous examples of where animal models were not predictive, or contributed little to the understanding or treatment of these diseases. If you or a loved one is sick and needs medication, you want the comfort of knowing that the medication has been proven safe and effective in humans, and how it worked in animals is irrelevant. Humans are not mice or rats or chimpanzees, and it doesn’t make much sense to conclude that the drug’s effect on animals will directly apply to how it works in humans. Although similarities are shared among species, it is the differences between species that are ultimately responsible for how each individual animal or human responds to drugs.
Recent breakthroughs in genetics have given scientists greater insight into how subtle genetic variations among humans can affect many aspects of disease risk and progression, as well as response to various treatments. When you appreciate that genetic differences among humans can generate such varied responses, it becomes abundantly clear that animals, being so genetically different from humans, cannot possibly be accurate predictors of what might happen in people. Moreover, even if animals could be predictive on any level, the better question to ask is to which humans the data could be applied, considering the genetic variability among humans (as well as environmental differences such as diet and culture, which may further complicate extrapolation).
Individuals and organizations opposed to vivisection are not the only critics of the scientific community’s lack of progress in translating research findings into safe and effective treatments for people. The Director of the National Institutes of Health, Dr. Francis Collins, recognized that “the use of animal models for therapeutic development and target validation is time consuming, costly, and may not accurately predict efficacy in humans.” He recently proposed the establishment of a National Center for Advancing Translational Sciences (NCATS), intended to revolutionize the diagnosis and treatment of a broad range of diseases through the generation and validation of more human-relevant models.
NAVS agrees that experimenting on animals too often fails to translate into cures and treatments for people. And even if it did, would it really be progress when it perpetuates the suffering of other sentient creatures? We are convinced that science can do better.
How Many Animals are Used in Research?
Who Counts? Who Doesn't?
Examples of Animals Used in Research
Examples of Areas of Research that Use Animals
Common Sense: Framing the Scientific Argument