"The occurrence of independent contributions by 2 or more scientists can be interpreted in terms of zeitgeist, genius, or chance. The relative adequacy of these 3 theories was examined by examining the general and intradisciplinary probability distribution of multiples and the relationship of individual eminence with multiple production and priority. An analysis of 579 multiples and of 789 scientists and inventors gave the most support to the chance theory, followed by the zeitgeist theory. Results are integrated into a single probabilistic perspective that incorporates some of the major features of all 3 theories. A small group of highly productive individuals is most likely to participate in multiples, including independent rediscoveries. These same persons are also unusually intimate with the 'technoscientific' zeitgeist and perhaps equally gifted with an inordinate amount of good luck."