In this blog post, based on the arguments of Ray Grick and Jean Swingle Grick, I will analyze the case for animal experimentation in human disease research and examine whether its premises and conclusions are indeed valid.
What are the premises of the argument in favor of animal experimentation?
Ray Greig and Jean Swingle Greig (2005) discuss animal experimentation from the perspectives of physicians and veterinarians. Their main argument is that “animal experimentation has been of no help in the study of human diseases, and since there are sufficient alternative research methods to replace it, animal experimentation is not justified.”
Since this paper develops its argument based on the views of Ray Grick and Jean Swingle Grick (2005), it is necessary to first examine the extent of their expertise regarding the topics they discuss. The two authors are known as physicians and veterinarians who have critically examined animal experimentation and have pointed out the problems that can arise when applying the results of animal experiments to humans. Through their writings and activities criticizing animal testing, they have raised questions about its scientific validity and its applicability to humans.
This article proceeds from a standpoint that advocates the views of Ray Greig and Jean Swingle Greig (2005). The author shares their opposition to animal testing. In this paper, the author aims to critique the arguments of those in favor of animal testing by analyzing the logic of the pro-animal testing side—which is contrary to this position—and identifying and summarizing the flaws in that logic. However, the term “animal testing” used here is limited to “animal testing for the study of human diseases,” consistent with the scope addressed in the writings of Ray Greig and Jean Swingle Greig.
In this paper, I will critique the arguments in favor of animal experimentation in order to defend the arguments against it. Therefore, it is first necessary to analyze what the arguments in favor of animal experimentation entail. To analyze the commonly used arguments in favor of animal experimentation, this paper utilizes the “arguments in defense of animal experimentation” summarized by Choi Hoon (2013). These “arguments in defense of animal experimentation” were reconstructed by Choi Hoon based on the argument in defense of animal experimentation written by Cohen in Cohen and Regan (2001), as well as the arguments presented by Kim Myeong-sik (2007) and Jeong Ju-wan, Choi Gyeong-seok, and Kwon Bok-gyu (2007). Carl Cohen and Tom Regan are scholars who have put forward numerous arguments regarding animal rights and animal experimentation, representing the pro- and anti-animal experimentation positions, respectively. Cohen, from a pro-animal experimentation standpoint, has developed arguments justifying the use of animals in biomedical research. In light of this, this paper assumes the “argument in favor of animal experimentation” summarized by Choi Hoon (2013) to be the general logic representing the pro-animal experimentation position and seeks to critique this logic based on the author’s own position. The “argument in favor of animal experimentation” is as follows:
(1) Humans and animals are biologically similar.
(2) Animal experimentation is essential for human life and health.
(3) There are no reliable and credible alternatives to animal experimentation.
(4) Therefore, animal experimentation is justified.
Let us analyze the argument in favor of animal experimentation. First, if proposition (1) is true, then proposition (2) is justified.
If humans and animals are biologically similar, there will be a certain degree of similarity in how diseases or drugs manifest in both humans and animals; therefore, one can argue that animal testing is necessary for human life and health. Next, if propositions (1) and (2) are true, and proposition (3) is also true, then conclusion (4) can be derived. If, as proponents of animal testing argue, if propositions (1), (2), and (3) are all true, then one must conclude that animal testing is justified. No matter how cruel animal testing may be, if there are no comparable alternatives and if animal testing is absolutely necessary for human life and health, then it can be justified.
At first glance, the argument in favor of animal testing may appear to be free of logical flaws. However, the problem with the argument in favor of animal testing does not lie solely in the formal process by which the three premises lead to the conclusion. The core issue with this argument lies precisely in whether the three premises are actually true. In this paper, I will examine and critique the flaws in the three propositions that form the basis of the argument in favor of animal testing, drawing on the arguments of Ray Greig and Jean Swingle Greig (2005). If we can demonstrate that these three propositions are problematic, we cannot reach the conclusion that animal testing is justified; thus, we can critique the validity of the argument in favor of animal testing. Through this, we will be able to support the position against animal testing advocated by Ray Greig and Jean Swingle Greig (2005).
Does the biological similarity between humans and animals justify animal testing?
(1) Humans and animals are biologically similar.
(2) Animal experimentation is absolutely necessary for human life and health.
As we saw in the previous analysis of the argument, since proposition (1) serves as the basis for proposition (2), the truth value of propositions (1) and (2) can be discussed in the same context. In other words, we must examine whether the mere fact that humans and animals are biologically similar is sufficient to conclude that animal experimentation is absolutely necessary for human life and health.
As stated in proposition (1), animal experimentation is conducted based largely on the biological similarity between humans and animals. However, whether this similarity provides sufficient scientific grounds to reliably predict experimental results applicable to humans is a separate issue. Ray Greig and Jean Swingle Greig (2005) criticize the argument that the similarity between humans and animals—as claimed by advocates of animal testing—is not a scientifically verified conclusion but rather an inference based on observed similarities.
It is not entirely impossible for us to make such inferences based on these superficial similarities. It is possible.
However, speculation remains mere speculation, and scientific conclusions are a different matter altogether.
There are clear biological similarities between humans and animals. However, these similarities do not imply that the progression of specific diseases, the effects of drugs, or toxic reactions are identical. In particular, since different species exhibit differences in genes, physiological functions, immune systems, and drug metabolism processes, it is difficult to conclude that results observed in animals can be directly applied to humans.
One of the key reasons why visible similarities between humans and animals are unlikely to constitute scientifically meaningful similarities is that the manifestation of diseases or the effects of drugs and vaccines can vary across different species. In fact, it is well established that pathological responses and susceptibility to tuberculosis differ depending on the animal species. Therefore, one should not assume that a specific drug or treatment will produce the same effect in humans simply because it was effective in animals.
As such, there are clear biological differences between animals and humans. Therefore, rather than simply dismissing the proposition that “humans and animals are biologically similar” as false, the problem lies in the assumption that the mere existence of biological similarity is sufficient to accurately predict outcomes in humans. Ultimately, the similarity between animals and humans cannot serve as sufficient grounds to justify animal testing.
Animal testing has been used in the process of verifying the efficacy and side effects of new drugs under development. Those who argue that animal testing is necessary to verify the safety of new drugs claim that by testing them on animals before using them on humans—whose effects and side effects are not yet fully understood—it is possible to predict their effects. However, as mentioned earlier, there are differences between humans and other animal species in the progression of diseases, drug mechanisms of action, and metabolic processes. Therefore, there are limitations to accurately predicting the efficacy and safety of new drugs in humans based solely on results from animal testing; consequently, it is difficult to consider the claim that animal testing is absolutely necessary for human life and health to be sufficiently substantiated.
In fact, the thalidomide incident is a prime example of how animal testing results during the drug development process failed to fully predict the risks to humans. Thalidomide, which was used as a sedative and morning sickness remedy from the late 1950s onward, led to a major drug safety crisis when women who took it during pregnancy gave birth to children with severe congenital malformations. This incident is often cited as an example illustrating the limitations of animal models, as animal testing at the time was insufficient to adequately predict the risks to human fetuses. However, since subsequent studies confirmed fetal abnormalities caused by thalidomide in some animals, such as rabbits and monkeys, this incident should not be oversimplified to suggest that “thalidomide-related problems did not appear at all in any animal experiments.”
Rather than being a case that demonstrates animal testing itself provided no information, the thalidomide incident serves as an example showing that animal testing results may not adequately predict risks to humans and that outcomes can vary depending on the species. Therefore, it is risky to assume that the safety of new drugs can be ensured by relying solely on the results of animal testing.
Apart from the thalidomide incident, there are many other cases where it is difficult to argue that animal testing always leads to an efficient drug development process. In the development of diabetes treatments, it has been argued that the focus on extracting insulin from animals delayed the development of technology for synthesizing human insulin. As such, Ray Greig and Jean Swingle Greig (2005) argue that animal testing is not always essential for human life and health, and in some cases, it can even slow down the development of research methods directly relevant to humans.
Are there any research methods that can replace animal testing?
(3) There are no definitive and reliable alternatives to animal testing.
Supporters of animal testing argue that there are no viable alternatives and ask opponents whether they would conduct experiments on humans if animal testing were not an option. If “experiments on humans” were to mean confining living humans—as is currently done in animal testing—and administering drugs or pathogens to observe the resulting effects, this would raise significant ethical and legal issues. However, the research on humans that opponents of animal testing advocate for is not that kind of experiment. There are many ways to obtain information directly relevant to humans without raising ethical concerns. Clinical studies on patients, in vitro studies, autopsies, and epidemiological surveys are prime examples.
One method that can provide information more directly relevant to humans than animal testing is clinical research. Ray Greig and Jean Swingle Greig (2005) describe clinical pharmacology as follows:
This process, known as clinical pharmacology, is the only way to determine how safe and effective a drug is for humans and what dosage should be administered. Such research replicates many of the procedures that pharmaceutical companies perform on animals.
However, while animal models provide information specific to those animals, clinical pharmacology provides data that is actually applicable to humans. As is often the case, the data they provide are entirely different.
Methods other than clinical research also play an important role in the study of human diseases. In the case of in vitro research, advances in cell culture technology have made it possible to conduct various studies on cytotoxicity using human cells and tissues. In particular, recent advancements in three-dimensional cell models—such as human-derived organoids—have made it possible to more closely replicate the structure and function of human tissues, and these models are being utilized to study disease pathogenesis as well as the efficacy and toxicity of drugs. Although organoids cannot yet fully replicate the complex functions of the entire human body, they are evolving into a new research method for studying human physiology and disease.
These changes demonstrate that alternatives to animal testing are not merely theoretical possibilities. In 2026, the U.S. Food and Drug Administration (FDA) also issued guidelines aimed at reducing animal testing in the new drug development process and utilizing new research methodologies more directly relevant to humans, pointing toward a direction of validating and utilizing new approaches such as organoids and organ-on-a-chip technologies.
Autopsies are also one of the key methods for studying human diseases. Autopsies have not only aided research into various diseases—such as diabetes, hepatitis, and appendicitis—but have also been used as a method to effectively illustrate the characteristics of diseases that are difficult to confirm through clinical diagnosis alone. As such, there are various methods for studying human diseases, including clinical research, in vitro studies, autopsies, and epidemiological investigations.
Therefore, the claim that there are no research methods to replace animal testing is difficult to accept. Of course, each research method has its advantages and limitations, and no single alternative method can completely replace all animal experiments. However, methods that utilize data directly relevant to humans, as well as human-derived cells and tissues, to study human diseases are continually advancing, and the potential to reduce the need for animal experiments is also growing. Therefore, it is difficult to accept the proposition that “there are no definite and reliable alternatives to animal experiments” at face value.
Can Animal Testing Really Be Justified?
In this blog post, I have critiqued the arguments in favor of animal testing summarized by Choi Hoon (2013), based on the logic and evidence presented by Ray Grick and Jean Swingle Grick (2005). The argument in favor of animal testing consists of four propositions and is structured on the logic that, assuming the first three propositions are true, the concluding proposition—“Therefore, animal testing is justified”—is also true. However, this article critiques that conclusion by examining whether the three premises constituting the argument have been sufficiently substantiated.
While there are clear biological similarities between humans and animals, these similarities do not guarantee that the results of animal experiments will apply identically to humans. Although animal experiments can provide certain insights for research on human health, there are limitations to accurately predicting the effects and risks that will manifest in humans based solely on the results of animal experiments. Furthermore, various research methods exist for studying human diseases, such as clinical trials, in vitro studies, autopsies, and epidemiological surveys; recently, new alternative and complementary research methods, such as human-derived organoids and organ-on-a-chip technologies, have also been developing.
Therefore, it is difficult to accept at face value the premise that animal testing is absolutely necessary for human life and health and that no alternative research methods exist. To assess the ethical justification of animal experimentation, one must not rely solely on the fact that humans and animals are biologically similar; rather, one must also examine how accurately the scientific benefits derived from animal experimentation can be applied to humans, as well as whether the same or more useful information can be obtained through other research methods more directly relevant to humans.
In this regard, animal experimentation can be considered a research method that requires ongoing scrutiny not only from an ethical perspective but also in terms of scientific efficiency and its applicability to humans.
