A. It has long been held that decisions made collectively by large groups of people are more likely to turn out to be accurate than decisions made by individuals. The idea goes back to the jury theorem of Nicolas de Condorcet, an 18th-century French philosopher who was one of the first to apply mathematics to the social sciences. Condorcet's theory describes collective decisions. If, for example, each member of a jury has only partial information, the majority decision is more likely to be correct than a decision arrived at by a single juror. Moreover, the probability of a correct decision increases with the size of the jury.
B. Now it is becoming clear that group decisions are also extremely valuable for the success of social animals, such as ants, bees, birds and dolphins. Bees make collective decisions, and they do it rather well, according to Christian List of the London School of Economics, who has studied group decision-making in humans and animals. Researchers led by Dr List looked at colonies. Among the bees that depart to form a new colony are some that have searched for and found some new nest sites, and reported back using a characteristic body movement known as a 'waggle dance' to indicate to the other bees the suitable places they have located. The longer the dance, the better the site. After a while, other bees start to visit the sites signalled by their fellow workers and, on their return, also perform new waggle dances. The process eventually leads to a consensus on the best site and the breakaway swarm migrates. The decision is remarkably reliable, with the bees choosing the best site even when there are only small differences between alternative sites.
C. But exactly how do bees reach such a robust consensus? To find out, Dr List and his colleagues used a computer-generated model of the decision-making process. By experimenting with it they found that, when bees in the model were very good at finding nesting sites but did not share their information, this dramatically slowed down the migration, leaving the swarm homeless and vulnerable. Conversely, problems also arose when bees in the model blindly followed the waggle dances of others without first checking. The researchers concluded that the ability of bees to identify successfully and quickly the best site depends on both the bees' interdependence in communicating the whereabouts of the best sites, and their independence in confirming this information for themselves.
D. Another situation in which collective decisions are taken occurs when animals are either isolated from crucial sources of information or dominated by other members of the group. José Halloy of the Free University of Brussels in Belgium used robotic cockroaches to subvert the behaviour of living cockroaches. The artificial bugs were introduced to the live ones and soon became sufficiently socially integrated that they were perceived by the real cockroaches as equals. By manipulating the robots, which were in the minority, Halloy was able to persuade the living cockroaches to choose an inappropriate shelter, even one which they had rejected before being infiltrated by the robots.
E. The way insects work out effective collective decisions can be as complex and as important as the decisions themselves. At the University of Bristol in the UK, Nigel Franks and his colleagues studied how a species of ant establishes a new nest. Franks and his associates wanted to know how the insects reduce the problems associated with making a necessarily swift choice. If the ants' existing nest becomes suddenly threatened, the insects choose certain ants to act as scouts to find a new nest.
F. How quickly they accomplish the transfer to a new home depends not only on how soon the best available site is found, but also on how quickly the migration there can be achieved. Once the suitable new nest is identified, the chosen ants begin to lead others, which appear to stay behind, to the new site, by a method known as tandem running. The study emphasised the necessity, for people as well as insects, of having active leaders in order to execute decisions successfully.