50 CONTROLLED NATURAL SELECTION 
geneous environment, then living matter would 
assume an infinite number of different forms, 
corresponding to the infinite number of the 
diversities of its environment ; and each form 
would be infinitely restricted (see Fig. 3). 
Associated with this adaptation must be 
structural alteration; function and structure 
are inseparable—these are acquired char- 
acters. 
Nevertheless, in spite of this power of adap- 
tation, one cannot conceive a variation of a 
species, whatever its nature, displacing another 
species from its specific environment, which 
it completely fills and perfectly fits ; to accom- 
plish this, the variation would have to differ 
from the parent in a great number of struc- 
tures, be a great mutation and would have 
at the same time to fit perfectly a new 
environment, in fact more perfectly than the 
former occupier, which itself is a perfect fit ; 
can such a correlation come about through 
Chance ? 
Change in Environment.—Change in en- 
vironment may be quantitative; the specific 
environment may increase, decrease, or dis- 
appear entirely, in which case the species will 
become common, rare, or extinct. The change 
may be qualitative, and consist in the addi- 
