Chap. VII.] THEORY OF NATURAL SELECTION. 179 



member of the group acquired a long proboscis ? With respect to 

 S. Africa, which was formerly inhabited by numerous herds of the 

 giraffe, the answer is not difficult, and can best be given by an 

 illustration. In every meadow in England in which trees grow, 

 we see the lower branches trimmed or planed to an exact level by 

 the browsing of the horses or cattle ; and what advantage would it 

 be, for instance, to sheep, if kept there, to acquire slightly longer 

 necks? In every district some one kind of animal will almost 

 certainly be able to browse higher than the others ; and it is almost 

 equally certain that this one kind alone could have its neck 

 elongated for this purpose, through natural selection and the effects 

 of increased use. In S. Africa the competition for browsing on the 

 higher branches of the acacias and other trees must be between 

 giraffe and giraffe, and not with the other ungulate animals. 



Why, in other quarters of the world, various animals belonging 

 to this same order have not acquired either an elongated neck 

 or a proboscis, cannot be distinctly answered ; but it is as un- 

 reasonable to expect a distinct answer to such a question, as 

 why some event in the history of mankind did not occur in one 

 country, whilst it did in another. We are ignorant with respect to 

 the conditions which determine the numbers and range of each 

 spiecies ; and we cannot even conjecture what changes of structure 

 would be favourable to its increase in some new country. We can, 

 however, see in a general manner that various causes might have 

 interfered with the development of a long neck or proboscis. To 

 reach the foliage at a considerable height (without climbing, for 

 which hoofed animals are singularly ill-constructed) implies greatly 

 increased bulk of body; and we know that some areas support 

 singularly few large quadrupeds, for instance S. America, though it 

 is so luxuriant ; whilst S. Africa abounds with them to an un- 

 paralleled degree. Why this should be so, we do not know ; nor 

 why the later tertiary periods should have been much more favour- 

 able for their existence than the present time. Whatever the 

 sauses may have been, we can see that certain districts and times 

 would have been much more favourable than others for the develop- 

 ment of so large a quadruped as the giraffe. 



In order that an animal should acquire some structure specially 

 and largely developed, it is almost indispensable that several other 

 parts should be modified and co-adapted. Although every part of 

 the body varies slightly, it does not follow that the necessary parts 

 should always vary in the right direction and to the right degree. 

 With the different species of our domesticated animals we know 

 that the parts vary in a different manner and degree; and that 



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