descendants of the species under new
conditions of life and with newly acquired habits.

To give a few instances to illustrate these latter {197} remarks. If green
woodpeckers alone had existed, and we did not know that there were many
black and pied kinds, I dare say that we should have thought that the green
colour was a beautiful adaptation to hide this tree-frequenting bird from
its enemies; and consequently that it was a character of importance and
might have been acquired through natural selection; as it is, I have no
doubt that the colour is due to some quite distinct cause, probably to
sexual selection. A trailing bamboo in the Malay Archipelago climbs the
loftiest trees by the aid of exquisitely constructed hooks clustered around
the ends of the branches, and this contrivance, no doubt, is of the highest
service to the plant; but as we see nearly similar hooks on many trees
which are not climbers, the hooks on the bamboo may have arisen from
unknown laws of growth, and have been subsequently taken advantage of by
the plant undergoing further modification and becoming a climber. The naked
skin on the head of a vulture is generally looked at as a direct adaptation
for wallowing in putridity; and so it may be, or it may possibly be due to
the direct action of putrid matter; but we should be very cautious in
drawing any such inference, when we see that the skin on the head of the
clean-feeding male turkey is likewise naked. The sutures in the skulls of
young mammals have been advanced as a beautiful adaptation for aiding
parturition, and no doubt they facilitate, or may be indispensable for this
act; but as sutures occur in the skulls of young birds and reptiles, which
have only to escape from a broken egg, we may infer that this structure has
arisen from the laws of growth, and has been taken advantage of in the
parturition of the higher animals.

We are profoundly ignorant of the causes producing slight and unimportant
variations; and we are {198} immediately made conscious of this by
reflecting on the differences in the breeds of our domesticated animals in
different countries,--more especially in the less civilised countries where
there has been but little artificial selection. Careful observers are
convinced that a damp climate affects the growth of the hair, and that with
the hair the horns are correlated. Mountain breeds always differ from
lowland breeds; and a mountainous country would probably affect the hi