High-Speed Natural Selection in Financial Markets with Large State Spaces

Recent research has suggested that natural selection in financial markets may be a very slow process, taking hundreds of years. We show in a general equilibrium model that it may be much faster in markets with large state spaces. In many cases, the time it takes to wipe out irrational investors is inversely proportional to the number of stocks in the market, i.e., if it takes about 500 years with one stock, it takes about one year with 500 stocks. Thus, theoretically, natural selection can be very efficient even when there is high market uncertainty. The speed of the natural selection process is a known function of irrational investors' sentiment and of the real characteristics of the stock market. According to a calibration to U.S. stock data, it takes about fifty years for an irrational investor to be wiped out. This is in line with studies of individual investor underperformance.