354 BIOLOGY 



advance over the last. The struggle for existence and the sur- 

 vival of the fittest are repeated generation after generation, and 

 in each successive generation the only members to survive will 

 be those with qualities that make them better able to contend 

 in the struggle for existence than their rivals. Hence every 

 individual character which gives its possessor any slight advan- 

 tage over its rival will be sufficient to enable its possessors to 

 survive the struggle for existence, by bringing about the exter- 

 mination of the less fortunate individuals that did not have the 

 favorable character in question. This character will be trans- 

 mitted to subsequent generations, when the struggle will be 

 repeated again, and once more the best characters of the 

 next generation will be selected. As this goes on without 

 cessation age after age, there will be a constant accumula- 

 tion of favorable characters, and thus the race will in general 

 constantly advance. 



Natural Selection and Adaptation. This law of natural 

 selection is especially well fitted to explain the marvelous adap- 

 tations of organisms to their environment. Since the different 

 members of any species of animals or plants are not alike, it 

 will follow that at any period in the history of a race, some indi- 

 viduals will be more closely adapted to their environment than 

 others. Since there is always an overproduction of individuals, 

 so that many more are born than can live, it will follow that the 

 individuals best adapted to their environment will be the ones 

 that will survive, while those less adapted to the conditions of 

 life will be the ones to be exterminated in the struggle for exist- 

 ence. Hence it will follow that at the close of any generation 

 the individuals left alive will be those that have the most favor- 

 able adaptation to environment. These will necessarily be the 

 parents of the following generations, and, by the law of heredity, 

 the next generation will inherit the characteristics of these 

 parents and yrillTbe, on the average, a little better adapted to the 

 environment than the last generation. If this process is repeated 

 generation after generation, it will follow that each generation 



