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 Vnies, 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 réle 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 Galton, 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 
