70 MODES OF RESEARCH IN GENETICS 



differentiated, in respect to both parent and 

 offspring, from certain other groups in the 

 same table. It does not tell us what the basis 

 of this differentiation is. It may be inheritance, 

 as it is assumed to be in the illustration here under 

 discussion ; it may be local environmental differ- 

 ences or it may be anything whatever so far as 

 the correlation method per se helps us. The 

 only way to determine whether the "differences" 

 indicated by the correlation method are really 

 heritable is to apply the method of individual 

 pedigree analysis to the complex, heterogeneous 

 material of the table. If it is possible to isolate 

 and propagate distinct genotypes from the ma- 

 terial, then it may be concluded that the primary 

 basis of the differentiation or heterogeneity 

 detected by the correlation coefficient was in- 

 heritance. 



There can be, of course, no valid objection to 

 the study, in and for itself, of the correlation exist- 

 ing between genetically related individuals in 

 respect of somatic characters. Such studies may, 

 indeed, for one reason or another, have a high in- 

 trinsic interest. The point I would emphasize, 

 however, is that in dealing with such correlations 

 one should always keep clearly in mind that he is 

 not dealing directly and primarily with phenomena 

 of inheritance, but only indirectly and secondarily. 



To summarize this discussion, it may be said 

 that to attempt to draw conclusions in regard to 



