From shoals of fish to human society: social organisms need to make collective decisions. And it is not always the majority that prevails. In some cases, a small, resolute group may succeed in bending the whole community to their will.

Using computer models and behavioural studies of fish, a team of scientists, including researchers from the Max Planck Institute for the Physics of Complex Systems in Dresden, has discovered that uninformed individuals support the decision of the majority and may prevent a particularly determined minority from prevailing over the rest.

For a democratic society, this means that individuals who are undecided need not necessarily present a risk to the democratic decision-making process; on the contrary, they can offer protection against the dominance of a small but strong-willed group.

History holds many examples of how a handful or even a single determined individual has succeeded in gathering whole societies behind them and directing their fate. The commonly held view is that such groups will always prevail when they are faced with large numbers of poorly informed and undecided individuals. The latter tend to follow the decisions of others and adopt the resolute determination of the group - even if the group is itself in the minority.

A group of researchers, including colleagues from the Max Planck Institute for the Physics of Complex Systems, has now arrived at a different result. Using a variety of computer models, the scientists have demonstrated that uninformed individuals can also bring about a majority decision, even if the minority is more determined than the majority.

"Our simulations initially confirmed what we expected: A small group that resolutely pursues a specific objective can dominate a larger group. What surprised us was that a group of uninformed or undecided individuals can prevent this from happening," says Thilo Gross, who has meanwhile moved from the Max Planck Institute in Dresden to the University of Bristol.

Evidently the size of a group has a greater attraction than the determination of a smaller party. The urge to go along with a relatively even-tempered majority frequently prevails over the attraction of an extremely determined minority. For this to happen, however, there must be sufficient undecided individuals to join in with the majority.

The scientists used their computer models to simulate a decision-making situation offering two choices, with the facility to vary the number of individuals preferring one option or the other. They also varied the strength of feeling with which individuals preferred either option. The models were based on just a few generalised assumptions.

"Our results are therefore applicable to all systems in which individuals would rather follow one another than enter into conflict and make decisions in the interests of their neighbours. This is true of various social organisms such as, for example, shoals of fish, flocks of birds or herds of mammals. And of course our findings are also transferable to human societies," Ian Couzin from Princeton University explains.

As a reality check for the model, the researchers also studied the behaviour of shoaling fish. By introducing food, they trained two groups of golden shiners, Notemigonus crysoleucas, to swim towards either a yellow or a blue disc.

Under the conditions of the experiment, the fish began with a predilection for the colour yellow, so that those trained to swim to the yellow disc acquired a much stronger preference than those trained to swim to the blue disc.

An analysis of their behaviour confirmed the results of the computer model: five fish trained to prefer yellow - creatures with a stronger predilection for this colour - prevailed over six fish trained to prefer blue, but with a weaker focus on this colour: The whole shoal swam towards the yellow target.

However, when, in a second series of tests, the researchers introduced five or ten untrained fish, these altered the outcome of the collective decision. Despite their strong predilection, the fish trained to prefer yellow were unable to prevail. The untrained and therefore uninformed fish sided with the majority, and all of them then headed for the blue disc.

When transferred to humans, this means that uninformed and therefore undecided individuals play an important role in collective decisions. They can facilitate a democratic outcome and prevent a minority from taking control.

However, the calculations also show that the number of uninformed individuals must not be excessive. In such cases, decisions are no longer predictable and follow a random pattern.

Iain D. Couzin, Christos C. Ioannou, Guven Demirel, Thilo Gross, Colin J. Torney, Andrew Hartnett, Larissa Conradt, Simon A. Levin, Naomi E. Leonard; Uninformed Individuals Promote Democratic Consensus in Animal Groups. Science 16 December 2011: Vol. 334 no. 6062 pp. 1578-1580 DOI: 10.1126/science.1210280