THE LINEAGE OF MAN 

 By William King Gregory 



Professor of Vertebrate Palaeontology, Columbia University 



Early Stages of Life 



The story of the evolution of man may at some distant date 

 come to an end, but apparently it never had a definite begin- 

 ning. In order to get a reasonable historical perspective let 

 us open the story at a period which, for the sake of illustra- 

 tion, 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 pres- 

 ent 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 (some- 

 what 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, sink- 

 ing, and uplifting had gone on for hundreds of millions of 

 years. Occasionally there were terrific disturbances of the 



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