INTRODUCTION. 21 



and adopted new methods. Even the problems 

 which it tried to solve were radically changed. 

 Hitherto the attempt had been made to find in- 

 stances of purpose in nature. The marvellous 

 adaptations of living beings to their conditions 

 had long been felt, and the study of the purposes 

 of these adaptations had inspired many a mag- 

 nificent conception. But now the scientist lost 

 sight of the purpose in hunting for the cause. 

 Natural law is blind and can have no purpose. 

 To the scientist, filled with the thought of the 

 reign of law, purpose could not exist in nature. 

 Only cause and effect appeal to him. The present 

 phenomena are the result of forces acting in the 

 past, and the scientist's search should be not for 

 the purpose of an adaptation, but for the action 

 of the forces which produced it. To discover the 

 forces and laws which led to the development of 

 the present forms of animals and plants, to ex- 

 plain the method by which these forces of nature 

 have acted to bring about present results, these 

 became the objects of scientific research. It no 

 longer had any meaning to find that a special 

 organ was adapted to its conditions ; but it was 

 necessary to find out how it became adapted. 

 The difference in the attitude of these two points 

 of view is world-wide. The former fixes the 

 attention upon the end, the latter upon the means 

 by which the end was attained; the former is 

 what we sometimes call ideological, the latter 

 scientific ; the former was the attitude of the study 

 of animals and plants before the middle of this 

 century, the latter th*e spirit which actuates 

 modern biology. 



