14 



AN ANALYSIS OF THE EFFECT OF SELECTION. 



the 1002 inbred plus line; 2 individuals (in cultures 937 and 1074) 

 from the Dichcet stock; culture 1004, which was made up from exactly 

 the same sources as 1002 (see above), and differed from that culture 

 only in that a single male was used. 



This material was mated in various ways, but brother-sister matings 

 were practised infrequently, and then (see Appendix) not often in 

 successive generations. All the cultures in this set were descended 

 from the 864 inbred line; and the " generation" of each culture has 

 been taken as the greatest number of generations from 864 shown by 

 any line of the ancestry of that culture. This method is somewhat 

 misleading, since in every case the ''generation" thus given is higher 

 than the average number of selected generations, and still higher than 

 the average number of crossbred selected generations in the pedigree. 

 For example, the first culture in the series, 937, is recorded as F 3 , 

 since the father came from the F 2 generation of the 864 line; but the 

 mother was an unselected individual from the Dichset stock. Cul- 

 ture 1074 is recorded as F 5 , though the father was unselected and the 

 mother was from the inbred 864 line. Culture 1254 is recorded as 

 F 7 , though one parent belonged to F 5 , and the only grandparent 

 not an F 4 came from 1074, above. This method of grouping the data 

 has been adopted because it is convenient to handle, and because it 



TABLE 10. Crossbred Plus Series. 



is desirable for purposes of comparison and computation to have the 

 generations expressed in whole numbers. The errors involved all 

 tend to make it appear that selection has been applied longer than is 

 actually the case, and this should be borne in mind when studying 

 table 10 and the curve (fig. 5) for this series. The pedigrees may be 

 traced from the data in the Appendix, if anyone cares to make a differ- 

 ent classification. 



Selection has apparently been successful in raising the mean of this 

 series; but this conclusion is not certainly correct, because of the en- 

 vironmental possibilities discussed above. 



