7o THE HAZARDS OF LIFE 

 Mutation 



A DESCRIBED by De Vries, mutation consists of a varia- 

 tion in the size of the organs or tissues from parent to 

 offspring due to changes in the chromosomal constituents 

 of the germ cells. Mutation often modifies individual man 

 and animals. Natural selection, according to De Vries, 

 incorporates and stabilizes the favorable mutations into 

 the permanent equipment of the species. 



Mutation is most common in hybrids and least common 

 in line breeding, as seen in herd animals. In civilized man 

 and the thoroughbred horse out-crossbreeding is common. 

 We should therefore expect to find the highest incidence 

 of mutation in civilized man and in the thoroughbred horse. 



The instabilities of civilized man, in contrast to native 

 man, appear to indicate that the civilized state is so new 

 that inheritance exhibits striking mutations. In the opera- 

 tion of the bipolar mechanism in both the thoroughbred 

 horse and in civilized man, mutation of certain energy-con- 

 trolling organs may be so excessive as to defeat normal func- 

 tion and become a pathologic physiology and even a disease. 



Influence of Mutations on Behavior as 



Exemplified by a Thoroughbred 



Horse and a Gangster 



In Chap. 17 we saw how, through breeding by man, such 

 mutations in the brain, the heart, and the adrenal-sym- 

 pathetic system have occurred as to render predictable and 

 unpredictable certain behavior characteristics. Among the 

 many thoroughbred horses studied we cited the example of 

 Brown Eyes, a thoroughbred of great promise that, due to 

 mutation, was a failure in behavior. 



As stated above, mutation in animals appears most fre- 

 quently and in the greatest extremes in those animals 



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