For animal research that causes sentient nonhuman animal suffering to be justifiable, I believe that two conditions must be met. First, harming animals for human benefit must be morally justified; this is the speciesism justification. Second, animal research must have utility—that is, it must produce useful, empirically valid knowledge that successfully increases our understanding of human illness and treatments and that could not reasonably be obtained through other means; this is the utility justification. In other words, (some) animals must be sufficiently different from humans in morally relevant ways to allow the morality of speciesism, and (some) animals must be sufficiently similar to humans biologically for cross-species extrapolation to have utility. Both conditions are necessary, and neither by itself is sufficient to justify animal experimentation.
I focus exclusively on the utility justification. I do not defend the morality of using animals in experiments, nor do I review the alternatives and refinements that can minimize laboratory animal suffering. I will argue that I and the medical scientists with whom I work have a sound rationale to continue the work we do.