It would appear, then, that Lieutenant Colonel Grossman’s appeals to biology and psychology are flawed, and that the bulwark of his historical evidence—S.L. A. Marshall’s assertion that soldiers do not fire their weapons—can be verifiably disproven. The theory of an innate, biological resistance to killing has little support in either evolutionary biology or in what we know about psychology, and, discounting Marshall’s claims, there is little basis in military history for such a theory either. This is not to say that all people can or will kill, or even that all soldiers can or will kill. Combat is staggeringly complex, an environment where human beings are pushed beyond all tolerable limits. There is much that we do not know, and plenty that we should be doing more to learn about. Grossman is clearly leading the way in posing these questions. Much of his work on the processes of killing and the relevance of physical distance to killing is extremely insightful. There is material in On Combat about fear, heart rate, and combat effectiveness that might be groundbreaking, and it should be studied carefully by historians trying to understand human behaviour in war. No disrespect to Lieutenant-Colonel Grossman is intended by this article, and it is not meant to devalue his work. I personally believe that some of the elements of his books, particularly the physiology of combat, would actually be strengthened if they were not shackled to the idea that humans cannot kill one another. But there are still questions that need to be asked, and the subject should not be considered closed. Grossman’s overall picture of killing in war and society is heavily informed by a belief in an innate human resistance to killing that, as has been offered here, does not stand up well to scrutiny. More research on the processes of human killing is needed, and although On Killing and On Combat form an excellent starting point, there are too many problems with their interpretation for them to be considered the final word on the subject. I believe that, in the future, the Canadian Forces needs to take a more critical posture when it comes to incorporating Grossman’s studies into its own doctrine. It is imperative that our nation’s military culture remain one devoted to pursuing the best available evidence at all costs, rather than one merely following the most popular consensus.