suppression, so neither do they imply more; for
nothing is a condition of existence, in so far as its power of effecting
the modification of any animal is concerned, which does not also involve
more or less difficulty or struggle; for if there is no difficulty or
struggle there will be nothing to bring about change of habit, and hence
of structure. This identity of meaning may be also seen if we call to
mind that the conditions of existence can be only a synonym for "the
conditions of continuing to live," and "the conditions of continuing to
live" a synonym for "the conditions of continuing to live a longer
time," and "the conditions of continuing to live a longer time," for
"the conditions of survival," and "the conditions of survival," for "the
survival of the fittest," inasmuch as the being fittest is the condition
of being the longest survivor.

But we have already seen that "the survival of the fittest," is,
according to Mr. Darwin, a synonym for "natural selection"; hence it
follows that "the conditions of existence" imply neither more nor less
than what is implied by "natural selection" when this expression is
properly explained, and may be used instead of it; so that when Mr.
Darwin says that "natural selection" is the main but not exclusive means
of modification, he must mean, consciously or unconsciously, that "the
conditions of existence" are the main but not exclusive means of
modification. But this is only falling in with "the views and erroneous
grounds of opinion," as Mr. Darwin briefly calls them, of Lamarck
himself; a fact which Mr. Darwin's readers would have seen more readily
if he had kept to the use of the words "survival of the fittest" instead
of "natural selection." Of that expression Mr. Darwin says[356] that it
is "more accurate" than natural selection, but naively adds, "and
sometimes equally convenient."

I have said that there is a practical identity of meaning between
"natural selection" and "the conditions of existence," when both
expressions are fully extended. I say this, however, without prejudice
to my right of maintaining that, of the two expressions, the one is
accurate, lucid, and calculated to keep the thread of the argument well
in sight of the reader, while the other is inaccurate, and always, if I
may say so, less "convenient," as being always liable to lead the reader
astray. Nor should it be lost sight of that Lamarck and Dr. Erasmus
Darwin maintain that species and genera h