1 6 THE EVOLUTION OF MAN. 



the entire process of the evolution of the individual presents 

 to the eye a connected series of diverse animal forms ; and 

 these various animal forms exhibit very diverse conditions 

 of external and internal structure. The reason why every 

 human individual must pass through this series of forms in 

 the course of his embryonic evolution, was first explained 

 to us by the Theory of Descent of Lamarck and Darwin. 

 From this theory we first learn the efficient causes (causce 

 efficientes) of individual evolution ; by the aid of this theory 

 we first perceive that such mechanical causes alone suffice 

 to effect the evolution of the individual organism, and 

 that the co-operation of designing, or teleological causes 

 (causce finales), which were formerly universally assumed, 

 is unnecessary. Of course, these final causes still play an 

 important part in the prevailing school-philosophy ; but in 

 our new natural philosophy we are enabled to replace them 

 entirely by the efficient causes. 



I allude to this matter at this early stage, in order to 

 call attention to one of the most important advances made in 

 any branch of human knowledge during the past ten years. 

 The history of philosophy shows that in the cosmology of 

 our day, as in that of antiquity, final causes are almost 

 universally deemed to be the real ultimate causes of the 

 phenomena of organic life, and especially those of the life 

 of man. The prevailing Doctrine of Design, or Teleology, 

 assumes that the phenomena of organic life, and in particular 

 those of evolution, are explicable only by purposive causes, 

 and that, on the contrary, they in no way admit of a 

 mechanical explanation, that is, one entirely based on 

 natural science. The most difficult problems in this respect 

 which have been before us, and which seemed capable of 



