PBE8ENT ASPECTS OF EVOLUTION 279 



tlie forces of environment. It is not a cause in any 

 proper sense of tlie word, but a result of a myriad of 

 interacting forces. The combination of these forces in 

 a process of natural selection leading directly to a 

 moral and spiritual goal demands an explanation in 

 some ultimate cause. This explanation we have al- 

 ready tried to find. 



It is a process of extinction. It favors the fittest, 

 but only by leaving them to enjoy the food and place 

 formerly claimed, or still furnished, by the less fit. In 

 any advancing group, as the less fit are crowded out, 

 and the better fitted gain more place and food and 

 more rapid increase, the whole species becomes on an 

 average better conformed. More abundant nourish- 

 ment and increased vigor seem also to be accompanied 

 by increased variation. And by the extinction of the 

 less fit the probability is increased that more fit indi- 

 viduals will pair with one another and give rise to even 

 fitter offspring, possessing perhaps new and still more 

 valuable variations. 



But if, of a group of weaker forms, those alone sur- 

 vive which adopt a parasitic life, those which in adult 

 life move the least will survive and reproduce ; there 

 will result the survival of the least muscular and ner- 

 vous. This degeneration will continue until the 

 species has sunken into equilibrium, so to speak, with 

 its surroundings. Here natural selection works for 

 degeneration. Sessile animals have had a similar his- 

 tory. But these parasitic and sessile forms had 

 already been hopelessly distanced in the race for life. 

 Their presence cannot impede the leaders ; indeed 

 their survival is necessary to directly or indirectly fur- 

 nish food for the better conformed. In the animal 



