that evolution was often mutation-limited. Modern biologists such as Douglas J. Futuyma conclude that essentially all claims of evolution driven by large mutations can be explained by Darwinian evolution. Developments leading up to mutationism Geoffroy's monstrosities, 1822 Prior to Charles Darwin, most naturalists were saltationists, believing that species evolved and that speciation took place in sudden jumps. Jean-Baptiste Lamarck was a gradualist but similar to other scientists of the period had written that saltational evolution was possible. In 1822, in the second volume of his Philosophie anatomique, Étienne Geoffroy Saint-Hilaire endorsed a theory of saltational evolution that "monstrosities could become the founding fathers (or mothers) of new species by instantaneous transition from one form to the next." Geoffroy wrote that environmental pressures could produce sudden transformations to establish new species instantaneously. Darwin's anti-saltationist gradualism, 1859 In his 1859 book On the Origin of Species, Charles Darwin denied saltational evolution. He argued that evolutionary transformation always proceeds gradually, never in jumps: "natural selection acts solely by accumulating slight successive favourable variations, it can produce no great or sudden modification; it can act only by very short steps". Darwin continued in this belief throughout his life. Thomas Henry Huxley warned Darwin that he had taken on "an unnecessary difficulty in adopting Natura non facit saltum ["Nature does not take leaps"] so unreservedly." Huxley feared this assumption could discourage naturalists (catastrophists) who believed that major leaps and cataclysms played a significant role in the history of life. von Kölliker's heterogenesis, 1864 In 1864 Albert von Kölliker revived Geoffroy's theory that evolution proceeds by large steps, under the name of heterogenesis, but this time assuming the influence of a nonmaterial force to direct the course of evolution. Galton's "sports", 1892 Darwin's cousin, Francis Galton, considered Darwin's evidence for evolution, and came to an opposite conclusion about the type of variation on which natural selection must act. He carried out his own experiments and published a series of papers and books setting out his views. Already by 1869 when he published Hereditary Genius, he believed in evolution by saltation. In his 1889 book Natural Inheritance he argued that natural selection would benefit from accepting that the steps need not, as Darwin had stated, be minute. In his 1892 book Finger Prints, he stated directly that "The progress of evolution is not a smooth and uniform progression, but one that proceeds by jerks, through successive 'sports'