New comparative analysis of 100 primate species, including humans, finds that ordinary aggressive behaviours and lethal violence do not form a single behavioural continuum. The research shows that species prone to frequent non-lethal fights or displays of hostility are not necessarily more likely to commit lethal attacks. Instead, extreme acts such as infanticide and fatal confrontations appear to follow different evolutionary patterns from routine aggression.
The investigators examined patterns of conflict across a broad sample of primates, cataloguing incidences of mild aggression, territorial fights and lethal events. Their assessment distinguishes between everyday hostility—threat displays, minor skirmishes and dominance contests—and rare, severe behaviours that result in death. Across the dataset, rates of common aggression did not predict the occurrence of lethal violence, suggesting distinct selective pressures shape these behaviours in different lineages.
These results have implications for how researchers frame the origins of violent behaviour in humans and other animals. The study challenges simplified evolutionary narratives that link frequent, low-level aggression directly to the capacity for killing rivals. By separating behavioural categories, the findings encourage more nuanced approaches in fields such as evolution, behavioural ecology and the study of human violence, where assumptions about a single aggression spectrum have informed hypotheses and comparative models.
The authors caution that identifying separate evolutionary trajectories for non-lethal and lethal actions does not downplay the consequences of violence nor erase the need to understand its causes. Instead, the work highlights that different forms of aggression may arise from distinct ecological, social and life-history drivers. Further comparative research will be necessary to map those drivers and to determine how well patterns observed across other primates apply to hominins and to modern human societies, without drawing simplistic parallels between everyday antagonism and extreme lethal behaviour.
