Herd mentality and herd behavior have been prevalent descriptors for human behavior since people began to form tribes, migrate in groups, and perform cooperative marketing and agricultural functions. The idea of a "group mind" or "mob behavior" was first put forward by 19th-century French social psychologists Gabriel Tarde and Gustave Le Bon. Herd behavior in human societies has also been studied by Sigmund Freud and Wilfred Trotter, whose book Herd Instincts in Peace and War is a classic in the field of social psychology. Sociologist and Economist Thorstein Veblen's Theory of the Leisure Class illustrates how individuals imitate other group members of higher social status in their consumer behavior. More recently, Malcolm Gladwell in The Tipping Point, examines how cultural, social, and economic factors converge to create trends in consumer behavior. In 2004, the New Yorker 's financial columnist James Suroweicki published The Wisdom of Crowds.
21st-century academic fields such as marketing and behavioral finance attempt to identify and predict the rational and irrational behavior of investors. (See the work of Daniel Kahneman, Robert Shiller, Vernon L. Smith, and Amos Tversky.) Driven by emotional reactions such as greed and fear, investors can be seen to join in frantic purchasing and sales of stocks, creating bubbles and crashes. As a result, herd behavior is closely studied by behavioral finance experts in order to help predict future economic crises.