THE GENETICAL THEORY OF NATURAL SELECTION.

The Genetical Theory of Natural Selection by Sir Ronald Aylmer Fisher FRS (17 February 1890 – 29 July 1962), a British statistician and geneticist, is widely cited as one of the founding documents of  so-called "modern synthesis" of Darwinian natural selection and Mendelian genetic inheritance. This first edition published in 1930 by The Clarendon Press, is the book that essentially gave birth to the field of mathematical population genetics.

The book combines the ideas of Mendelian particulate inheritance with Charles Darwin's theory of natural selection, with Fisher being the first to argue that "Mendelism therefore validates Darwinism" and stating with regard to mutations that "The vast majority of large mutations are deleterious; small mutations are both far more frequent and more likely to be useful", thus refuting orthogenesis. 

It is commonly cited in contemporary biology books and scientific papers, outlining many concepts that are still considered important such as Fisherian runaway, Fisher's principle, reproductive value, Fisher's fundamental theorem of natural selection, Fisher's geometric model, the sexy son hypothesis, mimicry and the evolution of dominance.