440 



EDWIN CARLETON MacDOWELL 



be expected from larger numbers. The three periods marked 

 out above stand out clearly (fig. 5). The highest degree of cor- 

 relation appears in the first period; the middle period gives 

 strong correlation in generations 27-31, with smaller amounts 

 in the two preceding groups; the third period shows no- correla- 

 tion at all. With no knowledge of the influences back of the 

 coefficients in the middle period, it would be easy to assume that 

 these positive coefficients indicate genetic variability, whereas 

 according to the preceding discussion it appears that they are 

 probably due to non-genetic causes. 



TABLE 5 



Straight-line equations showing the regression of grade of offspring upon grade of 



parents; generations in groups of jive. S, grade of son; D, grade 



of daughter; p, grade of parents 



Conclusions 



Considering the tables and figures alone, it may be concluded 

 that generations 2-6 show more unquestionable positive 

 correlation than appears in any other group of generations in 

 the whole series. It is during these early generations that the 

 means indicated that selection was effective. The middle period 

 of generations taken at the face value of the correlation co- 

 efficients would not promise much success for selection, for, 

 although there are positively correlated generations, there are 

 also significantly negative correlations which would immedi- 



