EVOLUTION 363 



of recombination through crossing cannot, therefore, always be foretold. 

 The possibilities of evolution through hybridization are thus greatly 

 increased, and its range enormously widened. In view of these facts, 

 it is not surprising that some biologists have regarded the new characters 

 frequently arising in the fruitfly and the evening primrose as the result 

 of recombinations of genes, and not as mutations at all. But, as pointed 

 out before, even if this view should be correct, it would merely push back 

 to an earlier time the production of the characters whose genes are sup- 

 posed to be now shifting from one combination to another. For the 

 various factors producing eye color in flies can hardly have existed in 

 their present form from an indefinitely early time, even before flies 

 had come into existence in the evolution of animals. They must have 

 originated sometime in order to be recombined now, if this recombination 

 is all that is happening. Their origin was probably the sort of chemical 

 change which we call mutation. 



Artificial Evolution. — The possibility of evolution through hybridiza- 

 tion has been seized upon by man for his own advantage. The breeding 

 of animals has occupied his attention in a commercial way for centuries 

 and has resulted in striking improvements. But for a further statement 

 regarding animal breeding the reader is referred to the chapter on Genetics. 

 The attempt to bring about evolution by the artificial production of 

 mutations has been attended with doubtful success. A few biologists, 

 as pointed out above, believe they have altered the hereditary traits 

 of animals by changing such features of the environment as temperature, 

 nutrition and humidity; but their results have seldom been entirely 

 satisfactory. The majority of biologists, on contemplation of their 

 experiments, have usually been impelled to bring in the Scotch verdict 

 of "not proven." 



References 



Darwin, Charles. The Origin of Species. 



Darwin, Charles. "Variation of Animals and Plants Under Domestication. 



Lull, R. S. Organic Evolution. 



Morgan, T. H. A Critique of the Theory of Evolution. 



Scott, W. B. The Evolution Theory. 



