MULTIPLE FACTORS 201 



The test of reversing the direction of selection was 

 tried. The parents belonged to the 6 (and "6y/') 

 generation of the minus selection series, and aver- 

 aged —1.86. The average grade of the offspring was 

 — 1.56, a regression of 0.30, and their range was from 

 to —2.50. Some of the low-grade offspring ranging 

 from —0.37 to —0.87 were chosen for the return 

 selection. They produced 118 offspring whose aver- 

 age was —1.28, a regression of 0.68, which is in the 

 opposite direction from the regression obtained in the 

 former (minus) selection. For six generations the 

 reversed selection went on and carried the race back 

 along its former course, i.e., toward its original con- 

 dition. The fact that selection in the original direc- 

 tion w^as still producing some effect when the reversed 

 selection began, means, on the multiple factor 

 hypothesis, that the stock was still heterogeneous, in 

 some factors at least, and, therefore, reversing the proc- 

 ess would be expected to give the results that Castle 

 and Phillips obtained. 



These important results of Castle and Phillips ful- 

 fil so entirely the expectation for multiple factors 

 that they might have been utilized as a good illustra- 

 tion of the effects of selection on a group in which a 

 particular character owed its modifications to multi- 

 ple factors. Castle has, on a number of occasions, 

 made use of these results to expound a very different 

 interpretation. The experiments were begun, in fact, 

 to see whether selection in a given direction of a 

 varying character that gave a continuous series of 

 types would tend to further variation in the same 



