Human violence may not be a single, fixed natural trait shaped entirely by evolution, according to new research that challenges long-standing assumptions about violence. A study led by Bonaventura Majolo at the University of Lincoln suggests that different forms of aggression follow separate evolutionary paths rather than forming one continuous pattern.
Published in Evolution Letters, the research analyzed five types of aggression across 100 primate species that live in groups. These included mild conflicts within and between groups, killings of adults in both settings, and infanticide. By separating these behaviors, researchers aimed to test whether everyday aggression naturally escalates into lethal violence.
The findings indicate that low-level aggression is only weakly linked to deadly attacks. Species that frequently engage in minor disputes are not necessarily more likely to commit killings. This challenges the idea that aggression increases along a simple scale from harmless conflict to fatal violence.
Aggression shows distinct evolutionary patterns
Instead of a single pattern, the study found stronger connections among different forms of lethal aggression. Killings within groups and between groups were closely related, and both showed links to infanticide. These patterns were most pronounced when males carried out the attacks.
Researchers also examined the role of shared ancestry, known as phylogeny. The influence of evolutionary history appeared uneven. It played a limited role in shaping mild aggression but had a stronger effect on lethal behaviors, especially male infanticide. This suggests that deadly violence may be more deeply rooted in evolutionary history than everyday conflict.
The findings challenge a common question in science and public debate: whether humans are naturally violent or shaped mainly by culture. By treating aggression as multiple behaviors rather than one trait, the study presents a more complex view of how violence develops.
Rethinking how violence is understood
The research highlights that different types of aggression may serve different purposes and occur under different conditions. Mild conflicts can be part of normal social interaction without leading to more serious harm. This means a species can appear aggressive in daily life without being more prone to lethal violence.
The study also found that infanticide was more widespread than adult killings. It appeared in 65% of the species examined, compared with 22% for between-group adult killings and 19% for within-group killings. Researchers suggest this gap may reflect lower risks when targeting infants and the difficulty of observing rare lethal events in the wild.
Overall, the study does not deny the presence of violence among primates. Instead, it shows that aggression cannot be reduced to a single label. Different forms of violence likely have separate evolutionary origins, offering a more nuanced understanding of human behavior.