21,000,000 years, we are also able to put the whole ancestral series to a test by expressing each great stage in generations. The result is very satisfactory. The whole enormous stretch from the lowest fish-like creatures to man has been resolved into more than 5,000,000 successive generations, and each of these means a little step forwards in onward Evolution.
Nothing is to be gained for the understanding of our problem of Evolution if we multiply this enormous number of generations by ten or any other multiple. We are not able to conceive changes so small as those which necessarily have existed between Pithecanthropus and man if the whole striking difference is analysed into 17,000 steps. Every one of these stages in the modifications of the muscles, the skeletal framework, increase of brain, shortening of the trunk, lengthening of the legs, improvement of the hands, loss of the hairy coat, etc., is truly microscopical, imperceptible, just as
