Why Animals Fight: New Framework Unites Ecology, Psychology and Brain Science of Aggression

Aggression is one of the most consequential behaviors in the natural world. It decides who mates, who eats, and who survives, and it does so across species as different as crickets, ravens, chimpanzees, and humans. Yet the scientific study of aggression has long been split across three research traditions that rarely speak to one another: behavioral ecology, which models fighting decisions in evolutionary terms; human social psychology, which dissects the motives behind violent acts; and behavioral neuroscience, which maps the brain circuits that launch or restrain attacks. A new perspective article published in Frontiers in Ethology argues that these three fields, when integrated, can produce a far more complete and even mathematically rigorous account of why animals, including people, fight, threaten, escalate, and back down.

The article, authored as a synthesis across disciplines, builds on a deceptively simple observation: all three fields already distinguish between offensive, proactive aggression and defensive, reactive aggression. Offensive aggression is initiated to gain something, such as territory, food, or status, while defensive aggression is triggered in response to a threat and aims to protect the animal. What has changed, the authors argue, is the growing recognition in all three disciplines that each type of aggression is driven by a central motivational state, an internal neural state that persists over time and scales behavior from subtle threat displays to full attack or eventual submission.

This idea of a persistent motivational state is central to the new framework. Rather than viewing each aggressive act as a discrete response to an immediate trigger, the authors describe aggression as organized into sequences, such as the escalation from threat to attack, that are generated and scaled by underlying states in the nervous system. These states do not flicker on and off with each stimulus; they build, persist, and can override other motivations. The authors propose that such states can be modeled mathematically as attractor functions, neural dynamics that settle into stable patterns and resist brief perturbations, which helps explain both why aggressive moods last and why they can suddenly intensify.

Behavioral ecology has long approached aggression through the lens of evolutionarily stable strategies, asking when it pays, in evolutionary currency, to fight, display, retreat, or escalate. Classic models weigh the value of a resource against the costs of injury and energy expenditure, predicting that animals should adjust their willingness to fight based on what they stand to gain and what they risk losing. The concept of resource holding potential, essentially an animal’s fighting ability relative to its opponent, anchors much of this modeling. The new article argues that this framework, while powerful, has been missing something important: the internal neural machinery that actually implements these decisions in real time.

That is where behavioral neuroscience enters. Neuroscientists have identified subcortical brain systems, including circuits in the hypothalamus and midbrain, that plan, execute, and inhibit offensive and defensive aggression, with cortical networks modulating and constraining these deeper structures. The authors argue that these neural systems provide brain-based constraints on function that could make behavioral ecology models more physiologically realistic and reduce unexplained variance in behavioral data. In other words, if ecologists know what the brain can and cannot easily do, their models of fighting strategy should become sharper and more predictive.

The exchange runs in the other direction as well. Behavioral ecology raises questions that neuroscience is well positioned to answer, such as how animals value resources internally and how they decide to quit a contest. The timing and thresholds of submission, a decision that carries life-or-death consequences, likely reflect neural computations of cost that ecologists have modeled abstractly but that neurobiologists can now begin to localize in specific circuits. The authors suggest that this crosstalk could resolve long-standing puzzles about why animals sometimes persist in losing battles or withdraw from winnable ones.

Human social psychology brings its own vocabulary and findings to the table. The authors draw a direct typological equivalence between the ecological concept of resource holding potential and the psychological construct of formidability, the perception of an individual’s capacity to inflict harm. They also note that the ecological term retaliation cost efficiently captures the constraint that formidability imposes on human aggression, essentially formalizing the intuition that people are less likely to attack those capable of punishing them in return. These are not merely linguistic parallels; the authors argue they reflect shared underlying mechanisms shaped by common evolutionary pressures.

One of the most provocative claims in the article concerns positive reinforcement. Social psychologists and neuroscientists have recognized that offensive, proactive aggression can be positively reinforcing, meaning the act of aggression itself can be rewarding to the aggressor, not just the resource it secures. Behavioral ecology, the authors contend, has yet to reckon with the implications of this finding. If aggression is intrinsically rewarding, then evolutionary models that treat fighting purely as a means to an external end may be missing a key motivational driver, one that could explain why some individuals escalate beyond what resource value alone would predict.

The framework also grapples with phenomena that cut across species lines, including aggression contagion, in which the aggressive arousal of one individual spreads to nearby group members; redirection, in which an animal attacked by a dominant individual vents aggression on a bystander; and motivational override, in which a persistent aggressive state suppresses competing motivations such as fear or hunger. The authors argue that a common account of central motivational states, instantiated in subcortical circuits and modulated by cortical networks, can explain all three phenomena within a single mechanistic vocabulary, drawing on observations from many different taxa as befits a concern with pan-species evolutionary stability.

Human variation presents a genuine challenge to this unification. Personality differences and cultural norms shape human aggression in ways that simple ecological models, built on the assumption of species-typical strategies, struggle to accommodate. The authors acknowledge that behavioral ecology modeling must become more inclusive if it is to apply fully to humans, but they argue that the payoff justifies the effort. By integrating behavioral ecology, social psychology, and neuroscience into a shared framework, researchers may not only better understand aggression across the animal kingdom but also identify new avenues for reducing violence in human societies and improving welfare for animals held in captivity, where abnormal aggression is a persistent welfare concern.

Subject of Research: An integrative framework unifying behavioral ecology, social psychology, and neurobiology to explain the motivational and neural mechanisms of offensive and defensive aggression across species.

Article Title: Integrating the behavioral ecology, social psychology, and neurobiology of aggression

Article References: Potegal, M., & Elwood, R. W. (2026). Integrating the behavioral ecology, social psychology, and neurobiology of aggression. Frontiers in Ethology, 5, Article 1771240. https://doi.org/10.3389/fetho.2026.1771240

Image Credits: AI Generated

DOI: 10.3389/fetho.2026.1771240

Keywords: aggression, behavioral ecology, social psychology, neuroscience, resource holding potential, formidability, motivational state, attractor dynamics, evolutionarily stable strategies, offensive aggression, defensive aggression, animal behavior