Haldane concluded as Darwin had that the rate of evolution by natural selection in the world around us must be infinitesimally slow, far too slow to watch, that it could only be watched in the long, slow additions of the fossil record. Rates in the living world would have to be measured in millidarwins. In artificial selection, he said, you get rates of thousands of darwins, but that is not something you would see in the wild: "Rates of one darwin would be exceptional in nature."
Source: wiktionary