38 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 



did not distinguish between somatic and germinal variations. The 

 essential feature of mutations is that they are germinal in origin and 

 therefore come forth full-fledged in the first generation arising from 

 the changed germ. Darwin recognized "saltatory variations" or 

 "sports," which are mutations, but did not consider them of suffi- 

 ciently frequent occurrence to furnish an adequate material for 

 selection. 



De Vries, on his side, did not discard the principle of selection, 

 but showed that selection acted as between mutants, serving to elimi- 

 nate those which are unfit and allowing the sufficiently fit to survive 

 alongside the parent-types. According to Darwin's view, the new 

 types arose only at the expense of the old, for only through the elimina- 

 tion of the old (less fit) types could the new types progress toward 

 further fitness. Darwin's view was ill suited to explain the origin of 

 new distinct types, because the process of selection proceeded by 

 imperceptible steps. De Vries's view gives us distinctly different, 

 pure breeding types at once that, if isolated, would be new elementary 

 species from the first. 



In conclusion it may be said that the mutation theory was at 

 first intended as a substitute for natural selection, but that later the 

 selection idea was adopted as a directive principle, guiding mutations 

 toward adaptiveness. 



THE RISE AND VOGUE OF BIOMETRY 



No historical account of the development of the evolution idea 

 would be complete without a statement of the role played by biometry 

 in the study of evolutionary data. Biometry is the statistical study 

 of variation and heredity. During the last decade of the nineteenth 

 century it became obvious to those who had followed the progress 

 of the subject that farther advance toward the solution of the 

 problem of the causes of evolution must come from a better under- 

 standing of variation and heredity, the two fundamental factors 

 involved. Three main modes of attack were developed during these 

 years: the statistical (biometry), the experimental (chiefly breeding 

 work), and the microscopical (cytology or the study of the minute 

 structure of the germ cells). 



Sir Francis Gallon, a cousin of Charles Darwin, was the founder 

 of biometry. He applied certain already understood principles that 

 had been developed mainly in the study of the laws of chance to the 

 study of variations, and, by comparing the boiled-down formulas 



