DEVIOUS PATHS 
the “migratory species evince a greater amount of 
individual variation than do non-migrating species” 
because they are subject to more varying conditions 
of food and climate. I think we may say, then, if 
there were no struggle for life, if uniformity of 
temperature and means of subsistence everywhere 
prevailed, there would be little or no variation and 
no new species would arise. The causes of variation 
seem to be the inequality and imperfection of things; 
the pressure of life is unequally distributed, and 
this is one of Nature’s ways that accounts for much 
that we see about us. 
