Matthew, Darwin and Wallace are the only three people considered to have independently discovered the principle of natural selection as a mechanism for speciation (macroevolution). Others prior to Matthew had proposed natural selection as a mechanism for the generation of varieties or races within a species: James Hutton suggested the mechanism in 1794 as leading to improvement of varieties, and an 1813 paper by William Charles Wells proposed that it would form new varieties. In 1835, after Matthew's book, Edward Blyth published a description of the process as a mechanism preserving the unchanging essence of stable species.