MENDELISM AND SELECTION 



The result of the selection is shown graph- 

 ically in Fig. 41 (compare Table I). The 

 offspring in the narrow series became with 

 each generation narrower; those in the wide 

 series became with each generation wider, with 

 a single exception. In generation two the wide 

 stock was enlarged by the addition of a new 

 strain of animals. This caused a temporary 

 falling off in the average grade of the young, 

 the two series overlapping for that generation. 

 No new stock was at any other time intro- 

 duced in either series, the two remaining dis- 

 tinct at all times except in generation two. 

 It will be observed that a change in the aver- 

 age grade of the parents is attended by a 

 corresponding change in the average grade 

 of the offspring. The amount of variabil- 

 ity of the offspring is not materially affected 

 by the selection, but the average about which 

 variation occurs is steadily changed, as are 

 also the limits of the range of variation. 



The interesting feature of this experiment 

 is the production, as a result of selection, of 

 wholly new grades ; in the narrow series, of ani- 

 mals having less pigment than any known type 



125 



