When following the leader can lead into the jaws of death

Dr Ward added: “Our experiments examined whether groups of fish could be led by replica individuals of the same species. We explored following behaviour both in a neutral situation and in a potentially dangerous situation where the subject fish had to be persuaded to swim past a model of a predatory fish. That the test fish regarded the model predator as a threat was confirmed by our control experiments, where fish showed a strong aversion to the predator model. Despite this, solitary test fish were prepared to follow a replica leader towards the predator model, suggesting that an isolated member of a social species will pay almost any cost to stick close to a ‘friend’. When test fish were in larger groups of 4 and of 8 fish, however, the picture was very different: a solitary replica leader was ignored. Instead, it required 2-3 replica leaders to influence these larger groups.

“By adopting this ‘quorum response’, where subjects are prepared to follow a leader only when a threshold number of individuals behave in a particular way, animals can reduce the likelihood of spreading non-adaptive following behaviour. Whereas a single, maverick individual may act irrationally in a given situation, it is far less likely that two individuals will act so strangely.”

The researchers say that in order to benefit fully from information transfer, animals - and this would include humans - may have to follow quorum rules to filter out maverick behaviour.

The researchers conclude: “The reason why this study is important is that while quorum responses have been shown in invertebrates, like ants, bees and cockroaches, this is the first time (as far as we know) that it has been shown in so-called higher animals with relatively complex brains. The quorum decision rule is simple, but extremely effective, and it has important implications for human decision-making. In fact some of the group who have worked on the fish research have recently shown that groups of humans can be persuaded to take group decision guided by just one informed individual.

“We chose to test quorum decision-making with fish because they're easier to work with, but although we tend to think that we are more complex than fish in our decision-making, the reality is that we're more similar to them than we may choose to admit!

“Much human action is driven by simple decision rules and our work illustrates how those rules are common throughout the animal kingdom. A better understanding of this decision-making mechanism in humans and other animals helps us understand how people behave in crowds and shows why sometimes people in groups do apparently stupid things, such as stand in the street and stare skyward when there’s nothing to see, just because someone else is doing it.”

Full pdf preprints of the articles that accompany these titles and include these authors are available at: http://www.eurekalert.org/pio/pnas.php