THE EVOLUTION OF 

 LIVING ORGANISMS 



CHAPTER I 



THE NATURE AND ORIGIN OF LIFE 



THE variety of living things is so great, the manifesta- 

 tions of life so diverse and wonderful, that it may seem 

 at first sight impossible to explain them all as the result 

 of the continuous and uniform action of certain funda- 

 mental "natural causes." Yet this is the ambition of 

 the scientific student of nature. But, before attempting 

 to describe the process of evolution, and estimate the im- 

 portance of the several factors which have contributed to 

 bring about the development of life, let us see what 

 science can teach concerning the physical and chemical 

 properties of living organisms. 



All living things have certain characteristics in com- 

 mon as regards their structure and composition, their 

 properties and activities. They all feed, grow, and re- 

 produce. But if we say that in the possession of these 

 characteristics living matter differs from non-living 

 matter, we do not mean to imply that the difference is 

 absolute, that a perfectly hard and fast line can be drawn 

 between them, that the gap separating the living from 



