Now, the researchers find, the same is true in schools of stickleback fish making the decision about which leader to follow. Ward presented groups of three-spined sticklebacks with two fish replicas differing in characteristics, including size, fatness, shade, and spottiness, that reflect something about the health or fitness of the individual. For instance, a plump belly can indicate success in food gathering, while spots may indicate a parasitic infection.
He then ran trials in which one, two, four, or eight sticklebacks had to choose between two replica fish, one of which had been shown to be more attractive on the basis of the team's earlier studies. As group size increased, the fish made more accurate decisions, the researchers report, better discriminating subtle differences in the replicas' appearances.
In the majority of trials, either all or all but one of the fish followed the more attractive leader, they found. But the consensus method sometimes led the fish astray. In a substantial minority of trials, all or all but one of the fish followed the less attractive leadernot quite reaching Condorcet's philosophical ideal.
A simple quorum rule, in which an animal's probability of committing to a particular option increases sharply when a threshold number of other individuals have committed to it, proved sufficient to explain the observations, suggesting that animals can make accurate decisions without the need for complicated comparisons of the information they possess.
"Our results show rather that submission to peers and occasional cascades of incorrect decisions can be explained as a by-product of what is usually accurate consensus decision-making," the researchers wrote. Indeed, Sumpter said, humans make the same types of errors.
"A good example here is the stock exchange," he said. "Just now there is a lot of discussion about traders unable to make their own assessment and panic selling because ot
|Contact: Cathleen Genova|