Herd behaviour is the term used to describe situations in which the individuals of any particular group react coherently. Examples of behaviours described in this way include

• flocking in birds, animals evading a predator,
• also some human phenomena such as stock market bubbles, and behaviour in political demonstrations.

Herd behavior in animals

In the case of animals evading a predator, it can be shown that each individual can minimise the danger to itself by choosing the location and behaviour that is as close to the centre of the group as possible; this was the subject of a famous paper by evolutionary biologist W. D. Hamilton called Geometry for the selfish herd. In this case, clearly the "herd behaviour" is as far from a pack mentality as possible, since it emerges from the unco-ordinated behaviour of self-seeking individuals.

Herd behavior in human societies (crazes)

The phrase "herd behaviour" has acquired a certain currency in popular psychology, where herding instinct is offered as an explanation of such phenomena, also labelled as crazes.

A craze is an excessive fad or collective mania due to herd behavior.

• Some crazes have mild consequences (fashions).

• But others lead to the excesses of mass hysteria where the individual personality disappears and regresses to the lowest emotional instinctive denominator of crowd sentiment.

The latter form causes often destructive results, for example stock market bubble, stock market crash, street violence, demonizing and persecution of minorities, political or religious zealotry, etc.

However, some consider highly unlikely that these behaviours have much in common other than the superficial fact that they all involve a number of individuals doing more or less the same thing. In their view, attributing such collective behaviour to a "pack mentality" or "group mind" explains little, and might divert attention from the true explanation of the group's actions. Here are cases that shows that not all group behavior are the same

Some examples

In the case of stock market bubbles, the optimal behaviour for an individual may again be to do what everyone else is doing, because even though everyone knows that they are in a bubble, until it bursts, most profit is to be made by staying in the market; again the irrational "collective" behaviour emerges from unco-ordinated individual choices, even if it shows here some abandonment of risk aversion that is not totally rational, as the crash usually occurs without much warning. These phenomena are now much better understood as a result of investigations in experimental economics and behavioral finance, particularly by Nobel laureates Vernon Smith and Daniel Kahneman.

In the case of behaviour in demonstrations, the idea of a "group mind", groupthink or "mob behaviour" was put forward by the French social psychologists Gabriel Tarde and Gustav Le Bon, and was widely adopted by right-wing politicians, particularly in the inter-war years, to justify the repression of demonstrations.

In the case of guruism, a common ferment of such phenomena can come from collective mind control by charismatic leaders (in the broad meaning of charismatic as showing a capacity to influence and seduce others)) playing on emotional arguments to federate the opinions in the direction of their own goals

See also

• Groupthink
• Herd
• Hive mind
• Mob rule
• Mob mentality