56 CONTROLLED NATURAL SELECTION 
two specific environments. Species generally 
occupy common environments without com- 
petition because there is no crowding there. 
Common environments do not give rise to 
specific structures. 
3. New species are formed by differentiation 
of their specific environments. 
4. The environment becomes similarly sexu- 
ally and socially differentiated. 
5. Change in environment will produce 
either evolution or degeneration. If ontogeny 
and phylogeny give the history of a species, 
they should also give the history of its en- 
vironment. 
The earliest forms of life were probably all aquatic. 
The embryos of nearly all vertebrates and invertebrates 
have some characters and structures which indicate that 
their distant ancestors lived in water. 
The conceptions or confessions of faith 
embodied in most of the above arguments are 
of course not new; they have been recalled 
because they lead the way to the subject 
under consideration, namely, the power of 
enemies as selecting agents. 
Particular attention is directed to con- 
clusions Nos. 2 and 3, which state that 
common environments do not give rise to 
specific structures, or in other words, the 
