SEXUAL AND ASEXUAL REPRODUCTION 261 



evident. Inasmuch as the chromosomes contain the substance 

 which transfers the hereditary traits, it follows as a result of 

 this cell union that the individual that is to arise from the 

 fertilized egg will inherit traits of character, not from one but 

 from two parents. This will naturally produce a greater 

 variety in the offspring. If an individual arose simply as a 

 result of the division of a single parent, it would be expected 

 that it would have a tendency to show a much greater like- 

 ness to its parent than if it arose from the fusion of cells from 

 two parents, each of which possessed its own individual char- 

 acteristics. Thus, as a result of this sexual union, there will 

 be introduced into the offspring a tendency toward variety, 

 which would hardly be expected if they were produced always 

 by the non-sexual methods of simple division. It is believed 

 by biologists that one purpose of sex union is to produce 

 variety among organisms, i. e., to introduce what is technically 

 called variation. The importance of variation will be discussed 

 later; here it will be sufficient to say that upon the phenomena 

 of variation is based the whole problem of the evolution of 

 animals and plants, and therefore, without this phenomenon 

 of sex union, the evolution of animals and plants could hardly 

 have taken place, at least not in the form in which it has oc- 

 curred in the actual history of living things. 



The process thus becomes intelligible. Sex union brings 

 about the combination in the offspring, of the qualities of two 

 parents, and thus produces a succession of generations which, 

 though much alike, still show a certain amount of variation 

 among themselves and hence a variation from the ancestral 

 type. 



