144 EVOLUTION OF THE EARTH 



gregarious, probably submitting to the leadership of such as 

 by strength or cunning could enforce their authority, but not 

 until the terrestrial life was attained was the higher communal 

 life with cooperative division of labor possible. 



By means of this cooperation and his individual prowess 

 man has attained dominion over the organic world, while 

 through his subduction of nature's forces he conquers all of 

 her varied realms from the equator to the poles, adapting him- 

 self to environments which mold their creature denizens most 

 profoundly and through which he passes unimpressed by the 

 laws which compel their adaptation, for he is swifter than the 

 eagle in his flight and he passes through the waste of the 

 waters unscathed by nature, a victim, if such he be, only to 

 others of his own kind (Fig. 30). 



SUMMATION 



As the physician, by a clever device, can record graphically 

 the pulsations in the blood stream which are synchronous with 

 the throbbing of the human heart, so I have drawn a curve to 

 show the correspondence between the pulse of life and the 

 T^^T^ rrr p ^ T In this curve (Fig. 14) 



the evolutionary crises and periods of expansive evolution are 

 represented by upward movements, while extinctions are indi- 

 cated by the downward plunge of the racial line. This curve 

 is broken where as yet we have no tangible evidence to validate 

 our theory, solid when the fossil record changes theory into 

 fact. 



Thus the first recorded crisis, the origin of vertebrates, is 

 drawn coincident with the revolution at the close of the Pro- 

 terozoic era, but the actual vertebrate record begins in mid- 

 Ordovician time at the numeral i. The development of lungs 

 is connected with the disturbance at the close of the Silurian 

 uplift, the first recorded lung-fishes appearing at the numeral 2, 

 in the Lower Devonian, while the first footprint at 3, in the 



