Emergence of group rationality from irrational individuals

Evolutionary theory predicts that decision-makers should be rational. Despite this, violations of rationality have been found repeatedly in both humans and animals. While past research has focused on individuals, many highly integrated groups, such as ant colonies, regularly make collective choices. These decisions emerge from local interactions among many group members, none of whom take on the whole burden of decision-making. Here we show that lone ants are vulnerable to irrational errors, but intact ant colonies are not. We conclude that individuals are unable to adequately process the information needed for fully rational choice. Colonies evade these limitations by distributing their decision-making across many individuals. These results show how animal groups can suppress the systematic errors of cognitively limited group members.