290 Proofs of Evolution. 



A change in environment effects a corresponding change 

 in functional activities, which leads to structural modifica- 

 tion. Common observation and experience show us the 

 effect of the use or disuse of an organ or part. This is 

 likewise observable in determining the greater or less acute- 

 ness and activity of all the senses. An organ lying dormant 

 during many generations will gradually atrophy, and appear 

 as a rudiment, finally vanishing altogether. Fishes and 

 animals dwelling in underground caves into which no light 

 enters, are sightless, as they have no use for eyes. They 

 have lost them by disuse. The wonderful development of 

 the gymnast and athlete is achieved by intensified use of 

 the muscular system. If use or disuse is continued from 

 generation to generation, heredity will transmit the result. 



Natural Selection, or Survival of the Fittest, grows out 

 of the struggle for self-preservation. It is based on the 

 law of hunger. It develops strength, cunning, or agility. 

 It is an enemy to the weak and poorly conditioned. We see 

 this principle exemplified every day in the struggle for su- 

 premacy among individuals, communities, nations, and races. 

 The strongest and best-favored survive ; the weakest perish. 



Sexual Selection is not concerned with hunger, but with 

 beauty and the desire for offspring. As well stated by 

 Prof. LeConte, "In Natural Selection there is a struggle 

 of all for food, or means of living. In Sexual Selection 

 there is a struggle among the males for the possession of 

 the females and the means of procreation. The one is re- 

 lated to the nutritive appetite, the other, to the sexual 

 appetite." 



In animal life, Natural Selection most obtains among 

 mammals; sexual selection is more predominant among 

 birds, those having the most beautiful plumage, or sweetest 

 songs, winning the choicest mates. The former fight for 

 existence ; the latter, like the warriors bold of the Middle 

 Ages, battle for love. This warfare is in the world to-day 

 wherever there are life and movement. These principles 

 of evolution are still everywhere operating. Heredity 

 preserves these jewels of descent, without which we would 

 go back to " chaos and old night." 



PROOFS FROM (GEOLOGY. 



Among the strongest proofs of Universal development, 

 are those drawn from geological study. The earth has en- 



