WHAT IT IS AND WHAT IT IS NOT. 35 
It seems to me that the word evolution is now legiti- 
mately used in four different senses. It is the name of 
a branch of science; it is a theory of organic existence; 
it is a method of investigation; and it is the basis of a 
system of philosophy. 
As a science, evolution is the study of changing be- 
ings acted upon by unchanging laws. It is a matter of 
common observation that organisms 
change from day to day, and that day 
by day some alteration in their envi- 
ronment is produced. It is a conclusion 
from scientific investigation that these changes are 
greater than they appear, They affect not only the in- 
dividual animal or plant, but they affect all groups of 
living things, classes or races or species. No character 
iS permanent, no trait of life without change; and as 
the living organism and groups of organisms are under- 
going alteration, so does change take place in the ob- 
jects of the physical world about them. “Nothing 
endures,” says Huxley, ‘save the flow of energy and 
the rational order that pervades it.” The structures 
and objects change their forms and relations, and to 
forms and relations once abandoned they never return; 
but the methods of change are, so far as we can see, im- 
mutable. The laws of life, the laws of death, and the 
laws of matter never change. If the invisible forces 
which rule all visible things are themselves subject to 
modification and evolution we have not detected it. If 
these vary, their aberrations are so fine as to defy human 
observation and computation. In the control of the uni- 
verse we find no trace of “ variableness nor shadow of 
turning.” “It is the law of heaven and earth, whose 
way is solid, substantial, vast, and unchanging.” 
But the things we know do not endure. Only the 
shortness of human life allows us to speak of species or 
The science 
of organic 
evolution, 
