i6
The term “preservation” is obviously ambiguous, for it
may mean the preservation of the best and most useful,
and of these alone; or it may mean the preservation of the
best, and most useful, in company with those which are
not the best. Now we are told that both these kinds of
“preservation” take place alike in Art and in Nature.
It would facilitate the clear understanding of the sub
ject if the two kinds of selection were to be distinguished
by distinctive terms. We have to distinguish between
preservation of the fittest alone, and preservation of the
fittest and of some not the fittest. The latter is well
expressed by the phrase “ elimination of the worst.”
In order that Natural Selection should take place, there
must be a change of external conditions, otherwise there
would be no advantage in a modification of organism.
There must also be a struggle for existence, or there
could be no Natural Selection. It therefore becomes a
question of considerable interest to ask whether or not
external circumstances frequently change; and whether or
not the struggle for existence is always going on, seeing
that on these questions depends the continuous or the
intermittent action of Natural Selection.
Speaking of the change in external conditions, in his
demonstration of the origin of species by Natural Selection,
Mr. Wallace places on his list of proved facts : “Change
of external conditions universal and unceasing.”* In his
Darwinism he mentions: “Changes of climate which are
continually occurring, owing either to cosmical or geo
graphical causes,”-f- “under the ever-changing conditions
both of the inorganic and organic universe.”* But else
where he says: “Under conditions which do not perceptibly
vary from year to year and from century to century.”^
* Contributions, p. J02.
+ p. 22. i p. 122. § p. IOJ.