Modern Synthesis

The Modern Synthesis is the mid-twentieth-century unification of Darwinian natural selection with Mendelian genetics and population genetics, consolidating the view that evolution proceeds through the selection of heritable genetic variation — and only genetic variation. The Synthesis, developed by Fisher, Haldane, Wright, Dobzhansky, Mayr, and Simpson between roughly 1930 and 1950, established the gene as the exclusive unit of inheritance and natural selection as the primary creative force in evolution. Its defining move was the rejection of Lamarckian inheritance and orthogenesis: there is no directed variation, no inheritance of acquired characters, no goal toward which evolution tends.

The Modern Synthesis succeeded spectacularly as a research program for half a century. Its current status is contested: the Extended Evolutionary Synthesis argues that epigenetic inheritance, niche construction, and phenotypic plasticity require revisions to its core assumptions, while defenders argue these phenomena are fully accommodatable within the standard framework. The debate is unresolved but empirically tractable — and the empirical record is not uniformly friendly to the Synthesis in its strictest form. What is not in dispute is that the Synthesis was a genuine scientific achievement; what is disputed is whether it was a completed theory or a framework whose limits are only now becoming visible.