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The story of the evolution of man may at some distant date come to an end, but apparently it never had a definite beginning. In order to get a reasonable historical perspective let us open the story at a period which, for the sake of illustration, may be thought of as a billion years ago. At that time by far the greatest advance toward the human type had already been made, for living matter, according to our present evidence, was already in existence. All the myriads of years before that in which the components of living matter had gradually been built up had passed. The birth-throes of the central sun, which under the gravitational attraction of another passing sun had whirled out great tidal arms (somewhat like the streamers of a pin-wheel) and given rise to the planets, had long since been forgotten. The earth and the other planets had settled down nearly into their present orbits, and the surface temperature of the earth was not materially, if at all, higher than it is to-day. Moreover, the waters of the earth’s surface had long since been gathered together into oceans, the continents (whatever their outlines) were already in balance with the oceans, and the well-nigh eternal round of rock erosion, deposition, consolidation, sinking, and uplifting had gone on for hundreds of millions of years. Occasionally there were terrific disturbances of the