HERITAGE OF THE INDIVIDUAL 



269 



the progeny. This has long been known as ATAVISM. Finally, 

 characters of still more remote ancestors may crop out, and 

 constitute REVERSIONS. (Fig. 136.) 



3. Mutations 



But quite different results now and then occur. Characters 

 which have no place in the ancestry appear and are trans- 

 mitted to the descendants. Sometimes these new inherited 

 variations are only slight departures from the parental condi- 

 tion, while in other instances they are quite abrupt . However, 

 the studies of deVries and others 

 have led to the realization that 

 there is no fundamental difference 

 between the two classes It is 

 chiefly^ one of degree and so 

 we speak of alTTieritable varia- 

 tions, which are not the result of 

 recombinations, as mutations, 

 and contrast combinations and 

 mutations sharply with modifica- 

 tions which are not transmitted to 

 the offspring and are the results of environing conditions on 

 the soma during embryonic development or later. The im- 

 portance of this distinction can hardly be overemphasized 

 because it makes comprehensible many of the inconsistencies 

 in earlier work on genetics, as will immediately appear. 



B. GALTON'S 'LAWS' 



The studies of Galton, a cousin of Darwin, on the inheri- 

 tance of definite characters open the modern era of scientific 

 investigations in genetics. In particular, his work on the 

 inheritance of characters in Man, such as stature and. intel- 

 lectual capacity, is a biological classic judged by the momen- 

 tous consequences which followed from the discussion it 



136. Diagram to illustrate 

 three types of inheritance which fol- 

 low recombinations of parental char- 

 acters. A, alternative; B, mosaic; 

 C, blending. (From Conklin, after 

 Walter.) 



