Primates, human violence and aggression: What a new study reveals

For decades, experts have debated whether humans are violent from birth or become perpetrators through their environment, society and stress. A recent study of primates now suggests that the answer is far more complicated than the idea of violence escalating step by step.

How we have explained violence until now

Many people imagine aggression as a volume control: a shove comes first, followed by a punch and, potentially, a fatal attack. On this view, someone who argues frequently is more inclined towards extreme violence.

An international research team led by evolutionary biologist Bonaventura Majolo of the University of Lincoln is now challenging that picture. The researchers argue that aggression is not a single package of behaviours, but comprises different forms, some with entirely separate evolutionary histories.

The central message is that frequent minor conflicts in everyday life do not automatically make a species more “murderous”.

This puts the team at odds with earlier models, which generally treated aggression as one character trait that was simply stronger or weaker in different species.

What the primate study examined

Rather than focusing solely on humans, the researchers examined the entire primate family tree, encompassing monkeys, apes and humans.

The team analysed behavioural data from 100 primate species and distinguished five clearly defined forms of aggression. These included:

• Frequent everyday conflicts within a group
• Attacks on adult rivals
• The killing of infants (infanticide)
• Territorial violence between groups
• Threatening displays and gestures of dominance that cause no physical harm

Their aim was to establish whether species with many harmless conflicts really resort to lethal violence more often, or whether these behaviours evolved independently.

The surprising findings

The analysis produced a clear result. Species in which shoving, scuffling and minor attacks occur frequently do not automatically exhibit more lethal violence. The researchers found no evidence of a linear relationship.

A different pattern emerged instead: forms of lethal aggression, such as infanticide and targeted attacks on adult rivals, are partly related to one another, but are largely separate from everyday, comparatively harmless disputes.

Lethal violence appears to follow its own rules: it is not the “endpoint” of ordinary quarrels, but a response to particular social and ecological conditions.

The researchers regard this as a strong argument against simple rankings that place species on a scale from “peaceful” to “violent”. Such tables overlook the range of motives and circumstances in which aggression arises.

What this says about humans

The study goes to the heart of a sensitive question: are humans fundamentally violent beings kept in check only by rules, or primarily cooperative creatures who lash out under pressure?

The new data suggest that human behaviour cannot be reduced to a simple scale. Everyday aggression, such as a road rage incident or a heated workplace debate, has different roots from extreme acts including murder, war crimes and targeted killings in the gang world.

For the debate about human nature, this means that labelling people as simply “brutal by nature” overlooks crucial distinctions.

Aggression has many forms

Across the primate world, aggression takes very different forms: threatening gestures, vocalisations, hunting behaviour, struggles for rank, territorial defence and targeted attacks on the young of other groups.

Whether these behaviours occur, and how strongly they are expressed, depends on several influences, including:

The study suggests that extreme, lethal violence in particular is linked to specific triggers, such as intense competitive pressure or unstable social conditions. Consequently, lethal aggression can remain rare even in species with many minor conflicts, provided those particular conditions are absent.

What does this mean for everyday violence?

The distinction is highly relevant when considering human societies. Frequent verbal disputes, scuffles at school or heated discussions online are unpleasant, but they do not necessarily lead to an increase in serious violent offences.

This offers a practical approach to prevention: anyone seeking to reduce violence should not just tackle “aggression in general”, but also address the specific circumstances that encourage lethal escalation, such as:

• Extreme social inequality and a lack of prospects
• Armed groups that reward status gained through violence
• Breakdowns in the rule of law that leave offences unpunished
• Strong perceptions of rival groups as enemies

Everyday conflicts can usually be defused through better communication, clear rules and social support. Lethal violence, by contrast, requires an additional push, such as ideology, access to weapons, group pressure or a personal sense of having no way out.

Biology alone does not explain human violence

The researchers stress that human violence cannot be attributed solely to genes or to culture. Biological predispositions provide a repertoire of possible responses, but the environment is the main influence on whether that repertoire is used.

The question is less “Are we violent by nature?” than: under what conditions do people choose violence, and when do they choose not to?

Historical and present-day examples show that societies with similar biological characteristics can have very different rates of violence. Strict gun laws, stable institutions, good education and social security systems can substantially reduce extreme violence without “reprogramming” human beings.

What aggression means from the sofa to the street

In everyday life, it can help to distinguish between forms of aggression rather than condemning them all. Firmly disagreeing in a meeting or defending personal boundaries is not the same as physical brutality. Some forms of assertiveness can even protect against assault by sending clear signals.

The danger arises when three factors come together:

• Intense emotional arousal, such as anger, fear or despair
• A situation in which violence appears to be a “solution”
• A lack of internal or external brakes, such as empathy, social norms or consequences

Recognising and defusing precisely these situations is central to violence prevention, whether in families, schools, stadiums or conflict zones.

How the study changes our view of ourselves

The publication in the journal Evolution Letters offers no simple all-clear: humans are undoubtedly capable of frightening brutality. It does, however, correct the idea that lethal violence is an inevitable endpoint of everyday aggression.

This more nuanced understanding can make debates more measured. Instead of viewing humans simply as a “predator in a suit”, attention turns towards the specific triggers, social dynamics and political decisions that make violence more or less likely.

For politics, the justice system and education, there is a quiet but important reason for hope: if lethal violence is not a fate dictated by nature, conditions can be shaped to give the peaceful side of our behavioural repertoire more room.