 The tide of opinion turned with the adoption of mathematical modelling and controlled experimentation in population genetics, combining genetics, ecology and evolution in a framework acceptable to positivism.In 1918, R. A. Fisher wrote the paper "The Correlation between Relatives on the Supposition of Mendelian Inheritance," which showed mathematically how continuous variation could result from a number of discrete genetic loci.In this and subsequent papers culminating in his 1930 book "The Genetical Theory of Natural Selection", Fisher showed how Mendelian genetics was consistent with the idea of evolution driven by natural selection.