Historians and sociologists have remarked on the occurrence, in science, of “multiple independent discovery”. Robert K. Merton defined such “multiples” as instances in which similar discoveries are made by scientists working independently of each other. “Sometimes the discoveries are simultaneous or almost so; sometimes a scientist will make a new discovery which, unknown to him, somebody else has made years before.” Commonly cited examples of multiple independent discovery are the 17th-century independent formulation of calculus by Isaac Newton, Gottfried Wilhelm Leibniz and others, described by A. Rupert Hall; the 18th-century discovery of oxygen by Carl Wilhelm Scheele, Joseph Priestley, Antoine Lavoisier and others; and the theory of the evolution of species, independently advanced in the 19th century by Charles Darwin and Alfred Russel Wallace. Multiple independent discovery, however, is not limited to only a few historic instances involving giants of scientific research. Merton believed that it is multiple discoveries, rather than unique ones, that represent the common pattern in science. Merton contrasted a “multiple” with a “singleton”—a discovery that has been made uniquely by a single scientist or group of scientists working together. Merton’s hypothesis is also discussed extensively in Harriet Zuckerman’s Scientific Elite.