flowers, which they can, with a very little more trouble, enter by the
mouth. Bearing such facts in mind, I can see no reason to doubt that an
accidental deviation in the size and form of the body, or in the
curvature and length of the proboscis, etc., far too slight to be
appreciated by us, might profit a bee or other insect, so that an
individual so characterised would be able to obtain its food more
quickly, and so have a better chance of living and leaving descendants.
Its descendants would probably inherit a tendency to a similar slight
deviation of structure. The tubes of the corollas of the common red and
incarnate clovers (Trifolium pratense and incarnatum) do not on a hasty
glance appear to differ in length; yet the hive-bee can easily suck the
nectar out of the incarnate clover, but not out of the common red
clover, which is visited by humble-bees alone; so that whole fields of
the red clover offer in vain an abundant supply of precious nectar to
the hive-bee. Thus it might be a great advantage to the hive-bee to
have a slightly longer or differently constructed proboscis. On the
other hand, I have found by experiment that the fertility of clover
greatly depends on bees visiting and moving parts of the corolla, so as
to push the pollen on to the stigmatic surface. Hence, again, if
humble-bees were to become rare in any country, it might be a great
advantage to the red clover to have a shorter or more deeply divided
tube to its corolla, so that the hive-bee could visit its flowers. Thus
I can understand how a flower and a bee might slowly become, either
simultaneously or one after the other, modified and adapted in the most
perfect manner to each other, by the continued preservation of
individuals presenting mutual and slightly favourable deviations of
structure.
I am well aware that this doctrine of natural selection, exemplified in
the above imaginary instances, is open to the same objections which
were at first urged against Sir Charles Lyell s noble views on the
modern changes of the earth, as illustrative of geology; but we now
very seldom hear the action, for instance, of the coast-waves, called a
trifling and insignificant cause, when applied to the excavation of
gigantic valleys or to the formation of the longest lines of inland
cliffs. Natural selection can act only by the preservation and
accumulation of infinitesimally small inherited modifications, each
profitable to the preserved being; and as modern geology has almost
banished such views as the excavation of a great valley by a single
diluvial wave, so will natural selection, if it be a true principle,
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