many good people, and the "religion" of as many more equally good, it
may be worth while to consider what it still means, and what it does not
mean. For if we that use the word can agree on a definition, half our
quarrel is over.

It seems to me that the word evolution is now legitimately 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.

_The Science of Organic Evolution, or Bionomics._ As a science,
evolution is the study of changing beings 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 environment is
produced. It is a matter of scientific investigation that these changes
are greater than they appear. They affect not only the individual 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 or group of organisms is undergoing
alteration, so does change take place in the objects 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, immutable. 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. Its cosmic movements are so fine as to defy human
observation and computation. In the control of the universe 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 even of individuals as permanent
entities. The mountain chain is no more nearly eternal than the drift of
sand. It endures beyond the period of human observation. It antedates
and outlasts human history. So does the species of animal or plant
outlast and antedate the lifetime of one man. Its changes are slight
even in the lifetime of the race. Thus the species, through the
persistence of its type among its ch