vii LAW AND PRINCIPLE 185 



Natural laws like those of Newton, Joule and Ohm 

 bear any strain to which they may be subjected ; they 

 connect cause and consequence so closely that predictions 

 based upon them can be made with complete confidence. 

 Each of these three laws refer to inanimate or mechanical 

 conditions ; the things embraced by them belong to 

 the regions of dead matter and blind force, and when 

 we pass to the biological world where organisms possess 

 individuality call it soul or spirit if you will no such 

 perfect truths as are found in physical science can be 

 expected. It is possible, however, to arrive at broad 

 generalisations, and the greatest of these is that of 

 organic evolution and its causes. 



More than six hundred thousand different species of 

 animals have been described, while about half that 

 number of species of plants are known, and probably 

 natural science has not yet on its registers one half of 

 the numbers of animals and plants which actually exist. 

 Each of these separate species could be, and formerly was, 

 assumed to have been an object of special creation, but 

 a more reasonable view is that the various forms have 

 been evolved as the result of the action of natural pro- 

 cesses. 



The idea of evolution goes back to Aristotle and other 

 early Greek philosophers who attempted to face the 

 problems of the origin and development of forms of life. 

 No real advance was, however, made in the use of 

 the idea in the long period of theologians and natural 

 philosophers which lasted until about the beginning 

 of the seventeenth century, when Greek traditions were 

 largely shaken off and the modern method of inductive 

 observation and reasoning may be said to have begun. 

 Among the lay writers of that century who suggested 

 that species of animals and plants might undergo change 



