200 APPENDIX II—INTENSIVE SEGREGATION. 
(9) Environal selection.—As environal selection involves not only 
the superior propagation of the better fitted, but the inferior propa- 
gation of the less fitted and the non-propagation of the least fitted, 
it may be described as the exclusive propagation of those better fitted 
to the environment through the failure to propagate of the less fitted. 
Transformation by means of environal selection depends on the vary- 
ing degrees of adaptation to the environment in creatures that are in- 
tergenerating, the higher degrees being possessed by other than aver- 
age forms. Divergence is produced by environal selection only when 
to the above conditions producing transformation are added causes 
that prevent intercrossing between the sections that are being inde- 
pendently transformed. In other words, independent environal selec- 
tion produces divergence. 
(10) Sexual selection is the exclusive propagation of those better 
fitted to the sexual instincts of the species through the failure to 
propagate of the less fitted. In the words of Darwin, ‘‘It depends on 
the advantage which certain individuals have over others of the same 
sex and species solely in respect of reproduction.”* It is the form 
of reflexive selections which has received Darwin’s attention, and is 
consequently familiar to all. There are, however, certain points that 
need to be emphasized. 
This is the principle in accordance with which correspondence is 
secured between the external characters and the sexual instincts of a 
species, and also between the instincts of the two sexes, in so far as 
they relate to reproduction. This result is secured partly by the 
failure to propagate of those whose powers of attraction and conquest 
do not reach the standard demanded by the instincts of the other sex 
and partly by the failure of those whose instincts diverge too widely 
from the typical characteristics of the other sex. For example, on 
the highlands of North China I have observed a species of creeping 
cricket of the genus Bradyphorus, the male of which calls the female 
by a sharp stridulation, to which the female responds by approaching 
the male and finally climbing upon its back.. Now, we can well under- 
stand that the call of the male has been brought to its present shrill, 
penetrating perfection through the failure to attract mates in the case 
of males that were but feebly endowed, but it is equally certain tha’ 
those females whose sluggish instincts have been capable of respond- 
ing only to an unusually intense call have for the most part failed of 
leaving offspring, and, if any have been so unreasonable as to wait for 
the male to seek them out, they have, doubtless, perished without per- 


* “Descent of Man,” p. 3 of Chap. VIII. 
