 The 19th century ideas of natural selection and Mendelian genetics were put together with population genetics, early in the twentieth century.The modern synthesis also addressed the relationship between the broad-scale changes of macroevolution seen by palaeontologists and the small-scale microevolution of local populations of living organisms.The synthesis was defined differently by its founders, with Ernst Mayr in 1959, G. Ledyard Stebbins in 1966 and Theodosius Dobzhansky in 1974 offering differing numbers of basic postulates, though they all included natural selection, working on heritable variation supplied by mutation.