Conclusions following abstract ethical approaches such as deontology and utilitarianism are open to challenge on the grounds that the theories themselves are ethically flawed. The reasoning being that if the theories themselves are flawed, then their conclusions are also flawed, and hence those who wish to continue committing some presumably immoral act are free to continue doing so until the ethical theories in question are proven to their satisfaction. In The Commonsense Case against Animal Experimentation,  Mylan Engel Jr. moves to counter this line of reasoning, not through an attempt to demonstrate the absolute truth of any particular ethical theory, but by constructing an argument against animal experimentation which consists of premises presumably already held by the interlocutor, forcing her—if she is willing to be consistent—to accept eventually the conclusion that animal experimentation is unethical.
Engel begins by explicating three premises which he shows to be uncontroversial by virtue of the fact that they are already implied by the work of Carruthers and Cohen, two authors advocating animal experimentation. In triplicate combined, these are that it is wrong to intentionally harm, to cause suffering, or to kill sentient animals for no good reason. He then establishes three more premises that are entailed by the first set. Again in triplicate combined, these are that it wrong to perform harmful, painful, or lethal experiments on conscious sentient animals for no good reason. Engel concludes this section by noting that biomedical research generally is harmful, painful, and lethal for the animal subjects. The question then arises: are there good reasons for biomedical research? This question is analyzed in the next section, “The Scientific Case against Using Animals in Biomedical Research.”
Engel begins this section by noting that belief in the strong efficacy of biomedical research is pervasive among both the general public and the scientific community, but that is in in fact unjustified, a claim he demonstrates through two vectors: first, that some types of research offer only “idiosyncratic information that has no relevance to human beings,” and second, that other types of research which are thought to beneficial are actually not. Engel exemplifies the former with a discussion on measurements of LD50 in nonhuman animals. The LD50 is the level at which 50% of a given population of a species will perish upon the administration of some substance. For example, the LD50 of aspirin in rats is 200mg/kg, meaning that upon consumption of this dose of aspirin among a population of rats, 50% of them will die. This information, Engel notes, contributes nothing of value to human knowledge and thus violates the premises established in the previous section, in that it harms, causes pain, and kills animals for no good reason.
The next issue to be decided then is whether the benefits derived from other types of biomedical research (e.g. medicinal research) satisfice a standard that would preclude them from violating the same premises. Said another way, Engel’s inquiry becomes one of establishing whether animal research is in actu beneficial, for if not, then it is undertaken for no good reason. On this, he argues that the results derived from animal experimentation are misleading “in at least four ways along two distinct vectors,” safety and efficacy . The safety vector can mislead by generating false positives and false negatives. Meanwhile, the efficacy vector can mislead through “false efficacy predictors” and “false inefficacy predictors.”
Beginning with the safety vector, false negatives occur when a drug shows no or little negative effect in animal models, but would be in fact harmful to humans. Engel exemplifies this with the Thalidomide tragedy, in which an additive cleared for use by pregnant women because it was unproblematic in animal models went on to cause teratogenic (birth defects) effects in humans. False positives, on the other hand, refer to drugs that cause negative effects in animal models but would be perfectly safe in humans. Such circumstances are problematic as drugs, to be approved for human consumption, must first be demonstrated safe in animals. Hence, by relying on unreliable animal models, potentially safe drugs are shelved before they have a chance to be tested in humans. Engel exemplifies this possibility with a hypothetical scenario in which penicillin—perhaps the most important medical discovery of the 20th century—if subject to the necessity of animal testing, might have been discarded had it been tested first on species like rats or Guiney pigs where it has teratogenic and fatal effects, respectively.
Similarly, along the efficacy vector, false inefficacy predictors arise when an experiment produces evidence of inefficacy in animal models, when the drug would in fact be efficacious for humans. Like false positives, drugs with falsely inefficacious results are shelved before having the opportunity to be demonstrated in humans. False efficacy predictors, meanwhile, are those drugs which show efficacious results in animals while being inefficacious in humans.
After Engel establishes throughout this section that such cases are not rare, the conclusion to be drawn is that animal experimentation is an unreliable model of drug safety and efficacy in humans. On the one hand, by their failure to act as the canary in the coal mine, or so to speak, and on the other, by their susceptibility to negative effects that wouldn’t present in humans, animal models are poor informers of drug safety. Conversely, by their failure to accurately predict efficacy in humans, they are poor indicators of drug performance.
Having established the misleading nature of animal models, Engel has completed the syllogism he introduced in the first section:
(P1) It is wrong to intentionally harm conscious sentient animals for no
(P2) It is wrong to cause conscious sentient animals to suffer for no good reason.
(P3) It is wrong to kill conscious sentient animals for no good reason.
(P4) Animal experiments are some combination of harmful, painful, or lethal.
(P5 It is wrong to intentionally perform harmful experiments on conscious sentient animals for no good reason (from P1, P4).
(P6) It is wrong to perform painful experiments on conscious sentient animals for no good reason (from P2, P4).
(P7) It is wrong to perform painful experiments on conscious sentient animals for no good reason (from P3, P4).
(P8) Animal models offer no good reason to cause harm, pain, or lethality.
(C) Animal experimentation is wrong.
Finally, Engel considers alternatives modalities of research, noting first that even if there were no alternatives, animal research is still not worth pursuing due to the reasons elucidated above. Next he briefly offers examples of alternatives such is in virto, in silico, and microdosing. In each of these alternatives, he argues, the data collected reflects more accurately “information specific to humans,” and hence offers a better pre-clinical trial alternative than animal research.
In his conclusion, Engel summarizes his findings, and closes by reiterating the rhetorical power of his argument: that it applies just as well regardless of one’s personal “views on speciesism, animal equality, and animal rights,” and even to those who value “humans over nonhumans.” For if the premises introduced are accepted, as they presumably are, then consistency with those premises in light of the problems with animal experimentation demands one accept the conclusion that animal experimentation is immoral.