IV 

 GENETICS 



During the twentieth century the science of 

 genetics has given us a valuable account of the 

 transmission of hereditary characters, and associ- 

 ated cytological studies have disclosed many de- 

 tails of the material basis for these phenomena. 

 The association of genetics with the problems of 

 evolution is not wholly a happy one, for it has set 

 up in the minds of some scientists a new bias, no 

 less enthusiastically received and supported than 

 those of the past. Therefore, while genetics is one 

 of the most promising fields for the investigation 

 of evolution, it is like other fields in presenting 

 material which must be very carefully estimated. 



The fundamentals of Mendelian heredity are, 

 presumably, known to every serious student of the 

 problems of evolution. The basic concepts of ge- 

 netics are very different. We may regard the exist- 

 ence of genes as definitely established. Certainly 

 there are few if any competent judges who now 

 deny that the chromosomes are responsible for 

 the transmission of hereditary characters, whether 

 or not they accept the modern idea of genes as 

 subordinate units within the chromosomes. Grant- 



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