248 EVOLUTION OF TO-DAY. 



the numerous breeds of pigeons indicates the value 

 of such isolation in producing change. Wagner, 

 therefore, believes that the only conditions where 

 new species can arise is where one or two individ- 

 uals are by some sort of isolation prevented from 

 crossing with others of the same species. He sug- 

 gests that if we suppose a small number of indi- 

 viduals, or perhaps a single pair, to migrate into a 

 new country, and be prevented from returning, such 

 an isolation will be obtained. All injurious crossing 

 will be prevented. The offspring of this pair will 

 be obliged to breed with each other, and thus any 

 variations which may appear will have the chance 

 to accumulate. For a time all of the offspring will 

 tend to have the same variations, since produced 

 under the same conditions by the same parents. 

 These variations will not then be eliminated by 

 crossing, and the result will be, therefore, a rapid 

 development of a new species. In this manner, by 

 eliminating the factor of crossing favored with un- 

 favored varieties, one of the most fatal objections 

 to Darwin's theory is avoided. Wagner uses his 

 theory to account for the origin of man something 

 as follows : The progenitors of man, some sort of 

 an ape, lived in tropical Asia. One pair, or perhaps 

 a few pairs, migrated from their home in the north- 

 ern part of the continent, and their return was pre- 

 vented perhaps by glaciers. This pair were now in 

 a very different climate, and were obliged to strug- 

 gle more severely for their existence than they did 

 in the luxurious tropics. This active struggle pro- 

 duced rapid changes, and since they were not able 



