PLUS SELECTION OF 



"EXTRACTED HOODED" 



RATS. 



21 



regression of 0.71 toward 0. We should expect the regression of the 

 offspring of such parents to be less than that of the offspring of the 

 2.50 parents, and so it would be if it were not for one aberrant indi- 

 vidual. Larger numbers of offspring would undoubtedly have given 

 the expected result. 



From among the F 3 offspring were chosen parents for the next gen- 

 eration (F 4 ). The chosen parents ranged in mean grade from +2.25 to 

 +3.12 (Table 45), average +2.52. They produced 205 young ranging 

 in grade from 0.25 to +3.50, mean +1.86, a regression of 0.66. 



The parents for the next generation (Table 46) ranged in mean grade 

 from +2.00 to +3.00, the mean being +2.27. They produced 119 off- 

 spring of mean grade +2.06, a regression of only 0.21. 



TABLE B. Comparison of the present series with the more general plus selection scries. 



The parents chosen from among these offspring ranged in mean grade 

 from +2.37 to +3.25, average +2.69. They produced 194 offspring 

 of grade +0.50 or higher (F 6 , Table 47), the range for the first time 

 lying wholly in the plus direction. The mean grade of the offspring was 

 +2.41, a regression of 0.28. 



The parents of the next generation (F 7 , Table 48) range in mean grade 

 from +2.62 to +3.37, their average being +2.80. Their 154 offspring 

 range from +0.75 to +3.75, mean +2.46, a regression of 0.34. 



The parents of the last generation in this experiment (F 8 , Table 49) 

 were of mean grade +3.08. They produced 45 offspring of mean grade 

 +2.67, a regression of 0.41. 



As a result of a single cross with a wild race followed by six successive 

 selections, a narrow-striped or minus family has thus been converted 

 into a wide-striped or plus family. Considering the smaller number of 

 offspring from which selections could be made, progress was quite as 

 rapid in this series as in the larger plus selection series. The regression 

 is surprisingly similar, generation by generation, in the two series. (See 

 Table B.) But it seems improbable that the closeness of the agreement 

 has any significance. This series has the theoretical advantage of being 

 derived from a single individual of the minus selection series. 



