The Survival of the Fittest 



tentment, that of Crustacea before an impassable 

 barrier, an unscalable cliff. The path of verte- 

 brates, steep and difficult, led ever upward. 



The change from water to land brought with 

 It many difficulties and disadvantages. Motion, 

 so easy in the water, was hard under the new 

 conditions. The crawling, helpless amphibian 

 seems a poor creature compared with the darting 

 fish. But life in the air was furnishing more 

 oxygen, was preventing the loss of heat, and was 

 thus raising the temperature of the blood, was 

 leading to a higher and freer life. But at first 

 the disadvantages of the change were more ap- 

 parent than the gains. 



The immediate use of mammalian structure 

 was to insure survival by saving eggs or young. 

 Its grand final advantage was family life and 

 the social life which was based upon this. The 

 marked advantages came late. 



Hand and brain are exceedingly complex or- 

 gans, and are correspondingly slow in their de- 

 velopment. It takes time for them to attain and 

 prove their real value. They have vast capaci- 

 ties, but these are realized to only a very small 

 extent in their earlier stages. All these struc- 

 tures of higher mammals, while useful from the 



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