-42 Heredity and Eugenics 



range of variation of the species. Tiiat is, artificial selection can, as 

 DeVries points out, produce races and maintain them, but its power 

 to develop these races beyond the natural range of variability is yet 

 to be demonstrated. 



From the series of cultures represented in Fig. 77, it is shown that 

 it is easy by selection to create races from a species, which would as 

 long as the artificial selection lasted, breed true to the ideal chosen. 

 Another such an experiment and two races breeding true that were 

 produced are represented in Fig. 78. From the parent generation tw'o 

 selected groups, one melanic (B), the other albinic fA), W'ere taken, 

 and from these, two clearly defined races without trace of intermediate 

 condition were produced. During each of eight consecutive genera- 

 tions slightly variable, light and dark races were maintained. At the 

 end of this time the material was divided and selection was stoppjed 

 in one group and continued in the other, but the lots were not allowed 

 to interbreed. The removal of the selective factor at once resulted in 

 a regressive shifting of the mode of each unselected race and in 

 increased variability, and this change continued through the eleventh 

 generation, when both unselected lots had moved back to the mode of 

 the species. 



These experiments with color characters show very clearly that 

 artificial selection is with transmissible variations a powerful factor 

 and can greatly accentuate any character and maintain it in an 

 extreme condition, but that there are limits beyond which I was 

 not able to niodify the characters by this agency. The experiments 

 also show that artificial selection works rapidly, and not, as has Ijeen 

 so often assumed, with extreme slowness. True, in experiment I 

 practiced a most rigorous selection, but not more rigorous than that 

 which the natural selectionists believe exists in nature. 



The ex])erimental production of general color variations and their 

 preservation by selective breeding give many points of interest. In 

 this I have confined my attention almost entirely to extreme light 

 and dark forms. To produce light forms I have used hot and dry 

 conditions, and for dark forms warm and moist. The experiments 

 herein recorded dift'er from those already given in that the entire life 

 of the beetles was passed in the conditions of the experiment, and 

 not the larval and pupal stages alone as in the experiments upon 

 coloration. 



