TRANSFORMATION AND MONOTYPIC EVOLUTION. 187 
2. Eight Forms of Monotypic Evolution. 
Let us now consider how this initial segregation, which is always 
- present in the case of asmall colony, is enhanced and intensified by the 
codperation of other principles, and how forms segregated through 
possessing different characters in some one respect come to diverge in 
other respects. For example, when differences of color become the 
occasion for sexual and social segregation, how does this open the way 
for divergent transformation in habits of feeding and in a thousand 
other respects? The principles codperating with independent genera- 
tion in producing this enhanced divergence are all causes of simple 
transformation, or monotypic evolution when there is free intergen- 
eration. Divergent breeds of domestic animals have always been 
produced when the different sections of a species in the care of different 
races of men have been prevented from interbreeding, thus securing 
their independent transformation during the process of domestication. 
So in nature, when any form of independent generation has been 
established, any cause of transformation that may afterwards arise 
will always produce more or less divergent evolution, and never that 
which is in every respect parallel. But we must defer the discussion 
of this subject till we have enumerated the more manifest of the prin- 
ciples of monotypic evolution: 
(1) Assimilational transformation, or modification due to deficiency 
with economy, or redundance with profusion, of growth, resulting 
from different degrees of assimilative power. ‘‘ Economy of growth” 
is a term already in use, but a term is needed that shall include both 
this and its opposite. 
(2) Stumulational transformation, or modification produced by 
changed motions in the fluids of the organism responsive to changed 
influences in the environment. Under this principle we may place 
the direct influences of light, heat, electricity, the dampness of the air 
or the saltness of the water in which the organism is bathed, the qual- 
ity of the food, and all stimulation from physical and chemical causes, 
exclusive of those resulting in muscular activity or the movement of 
the organs. 
(3) Suetudinal transformation, or modification due to the effects of 
use, disuse, and habitual effort in producing motions, and in resisting 
the strain of gravity and other forces tending to produce motion. Sue- 
tude is not found in the dictionary, but I venture to use it as including 
assuetude, which is being accustomed to, being practiced in, habitual 
use; and deswetude, which is disuse, discontinuance of practice. 
