The motivation for biological aggression is an inherent and common aspect of the human behavioural repertoire.

According to a widespread opinion shared by the vast majority of historians, instances of aggression using pathogen weapons constitute extremely rare events in human history. Similarly, students of human behaviour tend to believe that their science plays no role in explaining this phenomenon, which is held to be exceptional and abnormal. Contrary to this dominant view, I argue that Hamiltonian spite - like Hamiltonian altruism - is an inherent part of the human behavioural repertoire and it includes the use of pathogens for spiteful purposes. This paradigm is supported by the following observations. The use of pathogens as weapons emerged far before the scientific understanding of the nature of infections and epidemics, though it has been underrepresented in written history ever since. It is also present in our expectations concerning the likely behaviour of an enemy and it is also a frequent component of threats. Several languages appear to bear linguistic references to our motivation for biological aggression in profanity. Finally, given that wartime epidemics kill people at a rate comparable to (or exceeding) that of mechanical weapons, all wars fought in recorded history incorporated an element of aggression through biological means. On the basis of these arguments, I claim that the motivation for biological aggression is an inherent and common aspect of past and present human behaviour.