160 NATURAL SELECTION. [Chap. IT. 



variations had ever occurred useful to each being's own 

 welfare, in the same manner as so many variations have 

 occurred useful to man. But if variations useful to any 

 organic being ever do occur, assuredly individuals thus 

 characterised will have the best chance of being pre- 

 served in the struggle for life ; and from the strong 



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principle of inheritance, these will tend to produce 

 offspring similarly characterised. This principle of 

 preservation, or the survival of the fittest, I have called 

 Natural Selection. It leads to the improvement of each 

 creature in relation to its organic and inorganic condi- 



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tions of life ; and consequently, in most cases, to what 

 must be regarded as an advance in organisation. Never- 

 theless, low and simple forms will long endure if well 

 fitted for their simple conditions of life. 



Natural selection, on the principle of qualities being 

 inherited at corresponding ages, can modify the egg, 

 seed, or young, as easily as the adult. Amongst many 

 animals, sexual selection will have given its aid to 

 ordinary selection, by assuring to the most vigorous and 

 best adapted males the greatest number of offspring. 

 Sexual selection will also give characters useful to the 

 males alone, in their struggles or rivalry with other 

 males ; and these characters will be transmitted to one 

 sex or to both sexes, according to the form of inheritance 

 which prevails. 



"Whether natural selection has really thus acted in 

 adapting the various forms of life to their several condi- 

 tions and stations, must be judged by the general tenor 

 and balance of evidence given in the following chapters. 

 But we have already seen how it entails extinction ; and 

 how largely extinction has acted in the world's history, 

 geology plainly declares. Natural selection, also, leads 



