CHAPTER XIII 
INFLUENCE OF SELECTION 
ARTIFICIAL selection is par excellence an experimental pro- 
cess, and has been applied with success to all of the known forms 
of variation. It has been used in the case of elementary varieties, 
that follow the law of discontinuous variation and inheritance 
as described in the preceding chapters. Whenever, in these 
cases, Mendel’s law holds, the formation of “pure” races can 
be quickly brought about by selecting the extracted dominants 
and extracted recessives. Where more than a single character 
is involved, the formation of a new race by selecting individuals 
containing two, three, or more desirable characters is more in- 
volved, and yet can be carried out with certainty. Selection 
produces nothing new in such cases, except in forming new com- 
binations of already existing characters. 
Selection may be applied to elementary species, which are new 
forms or sports that present one or more new characters. In 
this case isolation is the conserving principle of most impor- 
tance; but in cases where a single individual alone comes into 
existence, it must be crossed with the parent type, and from the 
offspring obtained selection of those that have the new character 
must be made. If the new character is transmitted to all the 
offspring, no selection amongst them may be necessary; but if 
the new character follows the Mendelian law of splitting in the 
second generation, selection and isolation may be necessary to 
obtain as quickly as possible a new race. In this form of selec- 
tion, also, nothing new is created, but what has appeared ‘‘spon- 
taneously” is preserved. 
The third form of selection is that applied to fluctuating 
variations. In the present chapter this topic especially will be 
198 
