Dominance hierarchy

A Dominance hierarchy is a rank order among animals, expressed when individuals yield to some others and prevail over others. The book distinguishes hierarchies arising from general memories of winning and losing from those grounded in recognition of particular opponents. Both can reduce repeated fighting, but the meaning of that reduction is contested: it may be an incidental result of individual strategies, or, in Wynne-Edwards’s interpretation, part of a population-level system that limits reproduction.

How Rank Emerges

In crickets, memories of past fights need not identify an opponent. A cricket with many recent wins becomes more likely to behave hawkishly; one on a losing streak becomes more dovish. R. D. Alexander demonstrated the effect by using a model cricket to beat real crickets: afterward, the treated animals were more likely to lose fights against other real crickets. The account interprets this as each animal continually revising its estimate of its fighting ability relative to the population average.

When crickets with this general memory live together in a closed group, their outcomes can sort into a rank order even if initial wins and losses were random. Those accustomed to winning become increasingly likely to win, while those accustomed to losing become increasingly likely to lose. Individuals lower in the order tend to give way to higher-ranking ones, and serious fights gradually become less frequent. Because crickets do not recognize one another as individuals, the book calls this a kind of dominance hierarchy rather than using the term in its stricter sense.

Recognition and Established Groups

A stricter hierarchy depends on specific memory: individuals recognize particular opponents and remember the outcome of earlier encounters. Hens and monkeys are given as examples. A monkey is more likely to lose to one that has beaten it before, making it advantageous to be relatively dovish toward a known previous victor.

The example of hens shows how recognition can settle relations within a group. When hens that have never met are brought together, fighting is initially frequent. As each learns its place relative to each of the others, the fighting subsides. The resulting order does not eliminate every contest: individuals sometimes fight earnestly, and an animal may rise above a former immediate superior. But submission by lower-ranking animals means that prolonged fights are uncommon and serious injuries seldom occur.

The book also associates stable membership with a measurable group difference. Established groups of hens, where fierce fighting is rare, have higher egg production than groups whose membership changes continually and whose members therefore fight more often. This association helps explain why biologists have described the reduction of overt aggression as the biological advantage, or function, of a hierarchy. The author cautions that this framing assigns evolutionary purpose to a group property rather than to individual behavior. The analysis is better made in terms of evolutionarily stable strategies in asymmetric contests where individuals recognize and remember one another.

Rank as Reproductive Entitlement

Wynne-Edwards gives dominance hierarchies a more explicitly population-regulating interpretation. In his account, high-ranking individuals are more likely to reproduce, either because females prefer them or because high-ranking males physically prevent lower-ranking males from approaching females. Rank thus becomes a ticket of entitlement to breed: rather than contesting directly over females, individuals compete over status and then, if they do not rank highly enough, accept that they are not entitled to reproduce.

This proposed restraint is not the absence of competition. Animals may still contest for higher status, which can improve their indirect prospects of breeding. Wynne-Edwards’s claim is that accepting the result of status contests limits reproduction: populations are kept somewhat below the point at which starvation would itself impose a limit. The interpretation therefore treats hierarchy not merely as a consequence of how individual animals respond to remembered contests, but as a means by which a population moderates its growth.

Two Explanations of the Same Order

The accounts differ over what can legitimately be inferred from a rank order. In the individual-strategy explanation, repeated wins and losses, or recognition of specific opponents, shape animals’ subsequent behavior. Reduced aggression follows from those individual adjustments; it need not be an adaptation for the good of the group. In Wynne-Edwards’s account, submission and social rank amount to accepted rules about who may breed, helping regulate population size.

The distinction is consequential: observing that a hierarchy reduces fighting does not by itself establish that reducing group aggression is its evolutionary function. Nor does the existence of rank alone prove Wynne-Edwards’s population-regulation explanation. The hierarchy is the visible group pattern; its causes and evolutionary significance depend on whether the evidence is interpreted through individual strategies in asymmetric contests or through a proposed system of reproductive restraint.