Chap. VI. 
OEGANS OF LITTLE IMPOETANCE. 
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 conse¬ 
quently 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 clus¬ 
tered around the ends of the branches, and this con¬ 
trivance, 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, 
w^e 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 immedi- 
