SELECTION EXPERIMENTS. 267 



mature beetles, and from these, two groups of copulating pairs of 10 each 

 (A and B) were selected and reared in the third generation, but showed no 

 modifications as the result of selection. These hibernated, and selections 

 from each lot were reared in the fourth generation, but showed no modifica- 

 tion. I now felt sure that the material was pure, that is, normal, and carried 

 no tendencies to appear in divergent extreme variations. Accordingly, from 

 the two series selection was made of as nearly modal individuals as possible, 

 and the two selected lots were mixed and divided into two lots of 10 pairs 

 each, C and D. These were placed, as soon as possible after emerging, in 

 surroundings productive of dark and light conditions of coloration, and 

 allowed to breed, producing in the fifth generation two distinct lots of 

 descendants, one light, the other dark. These hibernated, and after emerging 

 in the following spring were allowed to breed, when it was found that out of 

 50 mated pairs 31, or 62 per cent, were able to transmit their particular varia- 

 tion in full strength, a huge increase over that found in selections from 

 nature. From each group 5 pairs were selected as the parents of the sixth 

 generation. These gave, as was expected, distinct lots of individuals more . 

 melanic and more albinic than their parents, and each also produced indi- 

 viduals differing in many respects from the parent stock, and beyond the 

 usual range of variability. In the five following generations the same thing 

 was repeated, as may be seen from plate 29; that is, from each group of 

 selected parents there came a general population less and less variable, and a 

 greater or less number of highly divergent forms beyond the normal range of 

 variability of the species. These latter we shall consider in another place. 



In this series of cultures a normal parent stock has been subjected to 

 artificial selection aided by powerful environmental stimuli, both having the 

 production of the same end in view. The results, however, were a keen dis- 

 appointment ; the inability to produce in this experiment by selection and 

 powerful environmental influences a race much beyond the normal limits of 

 variability of the species might easily be taken to indicate the impotency of 

 selection. The ease with which the beetles moved back toward the species 

 mode when selection was no longer practiced and the conditions of existence 

 became modal, when joined to the data of place and geographical variations, 

 allows only of the conclusion that while differently colored races and modifica- 

 tions of this beetle occur in nature and are produced in experiment by artificial 

 selective processes and local environmental influences, such modifications are 

 limited by the natural limits of variation of the species and persists only as 

 long as the maintaining processes are present, and are utterly incapable of 

 existence under adverse or even natural conditions, reverting to the species 

 type. That is, artificial selections or local influences are able to modify, and 

 to a certain extent create races founded upon those variations which are 

 ordinarily killed off by natural selection (Chapter IV) ; but in the creation 



