to neglect of the details in historical biology, which he considered all-important. In the early 1990s this led him into a debate with Derek Briggs, who had begun to apply quantitative cladistic techniques to the Burgess Shale fossils, about the methods to be used in interpreting these fossils. Around this time cladistics rapidly became the dominant method of classification in evolutionary biology. Inexpensive but increasingly powerful personal computers made it possible to process large quantities of data about organisms and their characteristics. Around the same time the development of effective polymerase chain reaction techniques made it possible to apply cladistic methods of analysis to biochemical and genetic features as well. Technical work on land snails Most of Gould's empirical research pertained to land snails. He focused his early work on the Bermudian genus Poecilozonites, while his later work concentrated on the West Indian genus Cerion. According to Gould "Cerion is the land snail of maximal diversity in form throughout the entire world. There are 600 described species of this single genus. In fact, they're not really species, they all interbreed, but the names exist to express a real phenomenon which is this incredible morphological diversity. Some are shaped like golf balls, some are shaped like pencils. ... Now my main subject is the evolution of form, and the problem of how it is that you can get this diversity amid so little genetic difference, so far as we can tell, is a very interesting one. And if we could solve this we'd learn something general about the evolution of form." Given Cerion extensive geographic diversity, Gould later lamented that if Christopher Columbus had only catalogued a single Cerion it would have ended the scholarly debate about which island Columbus had first set foot on in America. Influence Gould is one of the most frequently cited scientists in the field of evolutionary theory. His 1979 "spandrels" paper has been cited more than 5,000 times. In Paleobiology—the flagship journal of his own speciality—only Charles Darwin and George Gaylord Simpson have been cited more often. Gould was also a considerably respected historian of science. Historian Ronald Numbers has been quoted as saying: "I can't say much about Gould's strengths as a scientist, but for a long time I've regarded him as the second most influential historian of science (next to Thomas Kuhn)." The Structure of Evolutionary Theory Shortly before his death, Gould published