4.3.8 - Ethological and evolutionary explanations of aggression

Aggression as adaptive instinct

A territorial fish attacks a coloured model; a person threatens a rival. Ethological and evolutionary accounts ask related questions, but a mechanism that releases a behaviour is different from an explanation of why a tendency may have been selected across generations.

Konrad Lorenz (1966) argued that aggression is an evolved instinct. In ethology, the focus is usually intraspecific aggression: aggression between members of the same species. The key claim is not that aggression is "bad temper". It is that aggressive displays can perform adaptive functions.

Two functions are especially useful for AQA.

Pettit, Bakshi, Dodge and Coie (1990) give useful support for the dominance idea in humans. They studied twenty groups of six unacquainted boys from first and third grade. The boys met for five 45-minute semi-structured play sessions, and their behaviour was video-coded. Dominance hierarchies emerged in the groups. This does not prove that human aggression is a fixed instinct, but it supports the broader ethological idea that competition and dominance can organise social relationships.

Lorenz argued that many animal fights are ritualised. Animals may bare teeth, raise fur, posture, charge, growl or display weapons such as antlers. These signals are threatening, but they often prevent a full fight. The loser may then give an appeasement display, such as exposing a vulnerable body part or lowering posture. The winner usually stops attacking. Avoiding serious injury can improve an individual's survival and future reproductive opportunities; natural selection does not require behaviour to evolve for the good of the species.

AO2 example: Two dogs meet in a new home. One stands tall, growls and shows its teeth. The other lowers its body, rolls over and stops challenging. If neither is injured and one dog later eats first or controls the best sleeping place, an ethological explanation would describe ritualistic aggression helping to establish a dominance hierarchy.

IRMs and FAPs

The ethological explanation becomes more precise through innate releasing mechanisms and fixed action patterns.

The environmental input to that mechanism is called a sign stimulus.

Once the mechanism is activated, the resulting behaviour is the fixed action pattern.

The causal chain is:

sign stimulus -> innate releasing mechanism -> fixed action pattern

Classic accounts describe fixed action patterns using the following features. They are features of the model, to be tested against observations, rather than proof that every aggressive response is completely rigid.

Tinbergen's sticklebacks

Tinbergen (1951; 1952) studied male three-spined sticklebacks during the breeding season. Males develop a red underside, establish territories and attack rival males. Tinbergen presented territorial males with models of different shapes. A realistic model without a red underside did not trigger much aggression, but even a crude model with a red underside did. The key sign stimulus was therefore the red underside, not the whole fish shape.

This supports the IRM-FAP account because a specific environmental cue released a predictable aggressive response. The red underside acted as the sign stimulus; the fish's built-in mechanism detected it; the result was a species-typical attack display.

AO2 shortcut: If a scenario says an animal attacks whenever one specific cue appears, identify the cue as the sign stimulus. Then explain the IRM-FAP chain.

Evaluating ethological aggression

Evidence for a releaser in one species must be distinguished from evidence that all aggression is rigid or self-limiting.

AO3 strength: controlled evidence for releasers. Tinbergen's stickleback research is strong because he systematically varied the stimulus. Shape and colour were separated, making it clearer that red was the effective releaser. This gives the ethological explanation more precision than simply saying "animals are aggressive by instinct".

AO3 strength: naturalistic observation. Ethologists often study behaviour in natural or semi-natural contexts. This matters because animal aggression can be tied to territory, mating state and social rank. A laboratory-only approach might miss the ecological function of the behaviour.

AO3 limitation: ritualistic aggression is not universal. Goodall and colleagues' observations at Gombe challenged the idea that intraspecific aggression is always harmless and self-limiting. Between 1974 and 1978, a split chimpanzee community experienced lethal intergroup conflict. Later reviews of chimpanzee intergroup relations also report coalitionary aggression, territorial competition and lethal attacks. This weakens any simple claim that same-species aggression normally ends in safe appeasement.

AO3 limitation: fixed action patterns may be less fixed than the name suggests. Later ethologists questioned whether the term "fixed" overstates rigidity. Schleidt (1974) asked how fixed a fixed action pattern really is, and Barlow's term modal action pattern is often used to emphasise that species-typical behaviours can still vary with context, motivation and experience. This weakens a fully deterministic version of Lorenz's account.

AO3 limitation: extrapolating from animals to humans is risky. Human aggression is affected by cognition, culture, learning, law, moral judgement and social norms. Cohen, Nisbett, Bowdle and Schwarz (1996) found that US southern White male students reacted more strongly to an insult than northern students on cognitive, hormonal and behavioural measures, supporting the role of "culture of honour" norms. This kind of cultural variation suggests human aggression is not simply an automatic IRM-FAP sequence.

The best conclusion is interactionist. Ethology gives a clear biological model for some animal aggression, especially where a specific cue triggers a species-typical display. It becomes weaker when it is used as a complete explanation for flexible, socially shaped human aggression.

Sexual jealousy and mate retention

Evolutionary accounts connect some aggressive behaviour to proposed ancestral problems involving partners and reproduction.

Evolutionary explanations of human aggression ask why aggression might have solved adaptive problems. Buss and Duntley (2006) argued that aggression may have served several functions, including acquiring resources, defending against attack, increasing status, deterring rivals, preventing partner defection and obtaining mates.

In the evolutionary account, that threat is linked to a specific proposed reproductive cost.

Sexual jealousy is central to evolutionary accounts of male aggression in heterosexual reproductive contexts. In the ancestral reproductive contexts assumed by this account, the person giving birth could identify their offspring directly, whereas a male partner could not directly observe genetic paternity. Males therefore faced a proposed risk of cuckoldry. If a male invested time, protection and resources in a rival's offspring, his reproductive success was reduced. Evolutionary psychologists argue that jealousy and mate retention strategies may have evolved to reduce this risk.