Masterpieces of Science 



protection much more than the male, and that 

 her preservation for a much longer period is 

 absolutely necessary for the continuance of the 

 race, we have an additional indication that the 

 resemblance is in all cases subservient to a great 

 purpose — the preservation of the species. 



In endeavouring to explain these phenomena 

 as having been brought about by variation and 

 natural selection, we start with the fact that 

 white varieties frequently occur, and when pro- 

 tected from enemies show no incapacity for 

 continued existence and increase. We know, 

 further, that varieties of many other tints 

 occasionally occur; and as "the survival of the 

 fittest" must inevitably weed out those whose 

 colours are prejudicial and preserve those whose 

 colours are a safeguard, we require no other 

 mode of accounting for the protective tints of 

 arctic and desert animals. But this being granted, 

 there is such a perfectly continuous and gradu- 

 ated series of examples of every kind of pro- 

 tective imitation, up to the most wonderful 

 cases of what is termed "mimicry," that we 

 can find no place at which to draw the line 

 and say, — so far variation and natural selection 

 will account for the phenomena, but for all the 

 rest we require a more potent cause. The 

 counter theories that have been proposed, that 

 of the "special creation" of each imitative 

 form, that of the action of similar "conditions 

 of existence" for some of the cases, and of the 

 laws of "hereditary descent and the reversion 

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