Cognitive scientists tend to focus on the behavior of single individuals thinking and perceiving on their own. This is natural because our own introspection provides us with unique insight into this level. However, interacting groups of people also create emergent structures that are not intentionally produced by any individual. People participate in collective behavior patterns that they may not even be able to perceive, let alone understand. Social phenomena such as rumors, linguistic conventions, the emergence of a standard currency, transportation systems, the World Wide Web, resource harvesting, crowding, and scientific establishments arise because of individuals beliefs and goals, but the eventual form that these phenomena take is rarely the goal of any individual.