192 ORGA^'S OF LITTLE LMPOKTANCE Chap. VL 



characters gained through sexual selection may be transmitted 

 to both sexes. Moreover, a modification, caused in any of tlic 

 above specified ways, may at first have been of no direct ad- 

 vantage to a species, ])ut may subsequently have been taken 

 advantage of by its descendants under new conditions of life 

 and newly-acquired luibits. 



If, for instance, green woodpeckers alone had existed, and 

 "\ve did not know that there Avere many black and pied kinds, 

 I dare say that we should have thought that the green color 

 was a beautiful adaptation to hide this tree-frequenting bird 

 from its enemies ; and consequently that it was a character of 

 importance and had been acquired through natural selection ; 

 as it is, the color is probably in chief part due to sexual selec- 

 tion. A trailing palm in the Malay Archipelago climbs tlie 

 loftiest trees by the aid of exquisitely-constructed hooks clus- 

 tered 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, 

 and which there is reason to l:)elieve, from tlie distribution of 

 the thorn-bearing species in Africa and South America, serves 

 as a defence against browsing quadrupeds, so tlie hooks on the 

 palm may first have been developed for this object, and subse- 

 quently been taken advantage of by the plant as it imderwent 

 further modification and became a climber. The naked skin 

 on the head of a vulture is generally considered as a direct 

 adaptation for wallowing in putridity ; and so it may be, or it 

 may possibly be due to tlie 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 adapta- 

 tion 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, Avliich have only to escape from 

 a broken C(i;ji:, 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 cause of each slight va- 

 riation or individual diflbrence ; and we are immediately made 

 conscious of this by reflecting on the diiferences in the breeds 

 of our domesticated animals in different countries — more espc- 

 ially in the less civilized countries where there has been but 

 littie methodical selection. Animals kept by savages in difler- 



