14 COSMIC FHILOSOPHY. [pt. il 



of the well-adjiisted mean would be incessantly cut off b} 

 natural selection, and species would be immutable. It is 

 needless to say that no such state of things has ever existed. 

 Constant change has been the order of things ever since our 

 planet first became fit to support organic life. No part of 

 the earth's surface is now, or ever has been, at rest. Oon- 

 tinents are rising and sinking, seas are growiog deeper and 

 shallower, soils are constantly altering in chemical composi- 

 tion, rivers are ever changing their beds, solar radiance is 

 ever gaining or losing in intensity, according to the earth's 

 ever-varying position in space, the density and moisture ol 

 the air are continually increasing and diminishing, and every 

 species of plant and animal is continually pressing upon the 

 limits of the area within which it is confined. All these 

 changes are going on to-day, and have been going on during 

 millions of ages. Though so slight as to be recognized only 

 by the most careful observation during the period covered 

 by human history, these changes have during longer periods 

 sufficed to submerge every continent and perhaps to make dry 

 land of every sea and ocean on the face of the globe. They 

 have raised mountains like the Andes and the Himalayas at 

 the rate of a few inches per century ; they have converted ex- 

 tensive tropical swamps into the desert of Sahara ; they have 

 repeatedly covered Europe and ISTorth America with glaciers ; 

 and they have hidden beneath solid rocks vast treasures of 

 carbon stealthily purloined from the dense atmosphere of an 

 older age. 



Since such changes have ever been going on, it follows that 

 organisms have been unable to remain constant and live. A 

 race of animals or plants in which no individuals ever varied 

 would sooner or later inevitably be exterminated, leaving no 

 progeny to fill its place. Observation shows, however, that 

 there is no such race. The members of each species are evei 

 slightly varying, but, so long as the environment remains 

 constant, natural selection prevents the variations from 



