 The full reconciliation was achieved in the 1920s and early 30s, thanks to the mathematical work of Fisher, Haldane and Wright (Fisher 1930, Haldane 1930–32, Wright 1931). These theorists developed formal models to explore how natural selection, and other evolutionary factors such as mutation and random drift, would modify the genetic composition of a Mendelian population over time. This work marked a major step forward in evolutionary biology, for it enabled the consequences of various evolutionary hypotheses to be explored quantitatively rather than just qualitatively. Verbal arguments about what natural selection could or could not achieve, or about the patterns of genetic variation to which it would give rise, were replaced with explicit mathematical arguments. The strategy of devising formal models to shed light on the evolutionary process remains the dominant methodology of population genetics today, though unlike in the 1930s, today’s modellers have a wealth of empirical data against which to test their predictions (Hartl 2020).