Chap. VI. ORGANS OF LITTLE IMPORTANCE. 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 Archipelego 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, 

 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 immedi- 



