172 NATURAL SELECTION vm 



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ditions in which it is placed. But it will now be a different 

 creature. It will be not only swifter and stronger, and more 

 f urr y it will also probably have changed in colour, in form, 

 perhaps have acquired a longer tail, or differently shaped 

 ears ; for it is an ascertained fact that when one part of an 

 animal is modified, some other parts almost always change, 

 as it were in sympathy with it. Mr. Darwin calls this 

 " correlation of growth," and gives as instances that hairless 

 dogs have imperfect teeth ; white cats, when blue-eyed, are 

 deaf ; small feet accompany short beaks in pigeons ; and other 

 equally interesting cases. 



Grant, therefore, the premises : 1st, That peculiarities of 

 every kind are more or less hereditary; 2d, That the off- 

 spring of every animal vary more or less in all parts of their 

 organisation ; 3d, That the universe in which these animals 

 live is not absolutely invariable ; none of which proposi- 

 tions can be denied ; and then consider that the animals in 

 any country (those at least which are not dying out) must at 

 each successive period be brought into harmony with the 

 surrounding conditions ; and we have all the elements for a 

 change of form and structure in the animals, keeping exact 

 pace with changes of whatever nature in the surrounding 

 universe. Such changes must be slow, for the changes in the 

 universe are very slow ; but just as these slow changes be- 

 come important, when we look at results after long periods 

 of action, as we do when we perceive the alterations of the 

 earth's surface during geological epochs, so the parallel 

 changes in animal form become more and more striking, in 

 proportion as the time they have been going on is great ; as 

 we see when we compare our living animals with those 

 which we disentomb from each successively older geological 

 formation. 



This is, briefly, the theory of natural selection, which 

 explains the changes in the organic world as being parallel 

 with, and in part dependent on, those in the inorganic. What 

 we now have to inquire is, Can this theory be applied in 

 any way to the question of the origin of the races of man 1 or 

 is there anything in human nature that takes him out of the 

 category of those organic existences over whose successive 

 mutations it has had such powerful sway ? 



