206 HERBERT SPENCER

possessed of one particular favourable character,
unless this is of extreme importance.'*

pt is admitted that we cannot prove that Natural
Selection effected this or that result in the distant
past, but we know that a process of discriminate
elimination is a fact of life, and we argue from the
present to the past. Given variations enough and
time enough, it is difficult to put limits to the efficacy
of selection. If in a race of birds fairly well adapted
to the conditions of their life, variations occur in the
length of wing, there is no theoretical difficulty in
supposing that if a longer wing is advantageous, this
particular favourable character may in the course of
time become through selection the property of the
whole race.]

(2) *' In many cases a structure is of no service until
it has reached a certain development; and it remains
to account for that increase of it by natural selection
which must be supposed to take place before it
reaches the stage of usefulness."

[One variation is often correlated with another, and
the stronger variation may afford point d'appui for the
action of natural selection, and thus act as a cover
for the incipient variation until that reaches the
stage of usefulness and becomes itself of selection-
value. What Spencer himself says in regard to the
selection of aggregates rather than items, seems half
the answer to his difficulty.

It has also been suggested that adaptive modifica-
tions may act as fostering nurses of germinal variations
in the same direction. Let us suppose a country in
which a change of climate made it year by year of the
utmost importance that the inhabitants should becomeSelection.