EVOLUTION MADE TLAIN 27 
mals—artificial selection—interferes with the 
work of natural selection. For one thing, man 
makes a radical change in the environment of 
every plant and animal he domesticates; for 
another, man selects for other purposes than 
the one Nature has in view—that is, if it 
can be said that Nature has a purpose. 
From the same parent stock man breeds one 
strain of cattle for beef, another for milk and 
butter; one variety of the horse for the saddle 
and another for draft purposes. Nature adapts 
the species to the environment—never the en¬ 
vironment to the species—sacrificing those in¬ 
dividuals that do not measure up to her stand¬ 
ard. She seems to care only for the species, 
not for the individuals, or only for those indi¬ 
viduals that give promise of a better species. 
This secret wrung from Nature (natural se¬ 
lection as a factor in progressive development) 
is man’s most precious truth, for it is the key 
to his further progress. 
To summarize: organisms tend to increase 
at a great rate; this intensifies the struggle for 
existence; organisms vary; in the struggle for 
existence the vast majority die early, leaving 
those that vary in the favorable direction to 
live and reproduce; this means change, prog¬ 
ress. This is natural selection. 
There is also De Vries’ “Mutations theory” 
which some scientists believe to have been an 
important factor in evolution. It is the theory 
that at times a species may progress by “jumps” 
—that is, that occasionally individuals come 
into existence that vary extremely from the 
mass, and that they may become the parents 
