Rates of Evolution

Darwin thought evolution is slow. Evolution is slow on long time scales, but the fundamental process works on a generation-to-generation scale, not long time scales. Phenotypic variation is geometric normal, with normality reflecting its underlying polygenic source; ln transformation is part of the measurement process. The natural rate unit is the haldane, particularly H0, representing change in standard deviations per generation on a timescale of one generation. When appropriately sampled, rates calculated on longer scales can be projected to a generational timescale. Empirical studies are reviewed concerning: (a) rates of polygenic mutation, (b) rates of response to human versus natural disturbance; and (c) rates of change in a classic study of punctuated equilibrium. Rate studies commonly find phenotypic change on the order of H0 = 0.1 to 0.3 standard deviations per generation. This is fast by any standard. Darwin was wrong on rates, but more right than we knew on natural selection.