246 s NATURAL SCIENCE [October 
although there is much evidence to the contrary; but, in either case, 
isolation by sexual selection is necessary for the preservation of any 
variations the males may possess. 
From this examination of the place of isolation in organic 
evolution I conclude that species generally originate by the pre- 
servation of individual variations by means of geographical or 
physiological isolation, which may be brought about in many ways ; 
and that, in most, but by no means all, cases they are improved and 
developed by competition and natural selection; and this competi- 
tion they find only in large and well-populated areas. 
I, W. Horio 
