THEORV OP NATURAL SELECTION.- 197 



All Mr. Mivait's objections will be, or have been, con. 

 sidered in the present volume The one new point whick 

 appears to have struck many readers is, " That natural selec- 

 tion is incompetent to account for the incipient stages of 

 useful structures." This subject is intimately connected 

 with that of the gradation of the characters, often accom- 

 panied by a change of function, for instance, the conversion 

 of a swim-bladder into lungs, points which were discussed 

 in the last chapter under two headings. Nevertheless, 1 

 will here consider in some detail several of the cases advanced 

 by Mr. Mivart. selecting those which are the most illustrative, 

 as want of space prevents me from considering all. 



The giraffe, by its lofty stature, much elongated neck, fore 

 legs, head, and tongue, has its whole frame beautifully 

 adapted for browsing on the higher branches of trees. It 

 can thus obtain food beyond the reach of the other Ungulata 

 or hoofed animals inhabiting the same country ; and this 

 must be a great advantage to it during dearths. The Niata 

 cattle in South America show us how small a difference in 

 structure may make, during such periods, a great difference 

 in preserving an animal's life. These cattle can browse as 

 well as others on grass, but from the projection of the lower 

 jaw they cannot, during the often recurrent droughts, browse 

 on the twigs of trees, reeds, etc., to which food the common 

 cattle and horses are then driven ; so that at these times the 

 Niatas perish, if not fed by their owners. Before ooming 

 to Mr. Mivart's objections, it may be well to explain once 

 again how natural selection will act in all ordinary cases. 

 Man has modified some of his animals, without necessarily 

 having attended to special points of structure, by simply 

 preserving and breeding from the fleetest individuals, as 

 with the race-horse and greyhound, or as with the game-cock, 

 by breeding from the victorious birds. So under nature with 

 the nascent giraffe, the individuals which were the highest 

 browsers and were able during dearths to reach even an inch 

 or two above the others, will often have been preserved ; for 

 they will have roamed over the whole country in search of 

 food. That the individuals of the same species often differ 

 slightly in the relative lengths of all their parts may be seen 

 in many works of natural history, in whick careful measure- 

 ments are given. These slight proportional differences, due 

 to the laws of growth and variation, are not of the slightest 

 use or importance to most species. But it will have been 

 otherwise with the nascent giraffe, considering its probablo 



