Change in some trait measure from M₀ to M₁ over some interval of time T₀ to T₁
             [Use of logarithmic scale removes size effects]

       Darwin (D) = proportional change of e / million years [e = 2.817....]
           E.g., an organism that increase 2.8-fold in size over 10⁶ years evolves at 1 D (1000 mD)

          Ex. (1) Cranial capacity in Homo:                                442 mD over 1 Myr
                       850cc  1330cc in 1 Myr => increase of  ~0.01 cc / generation

                  (2) Dental evolution in horses (Equidae):            40 - 1000 mD over 55 Myr
                        Molars become hypsodont (high-crowned) co-incident with evolution of grasslands

                  (3) Body size in European sparrows (Passer):    100,000 mD over 100 yr
                        Rapid size increase after introduction to New World