Variation and Natural Selection. 1 1 1 



species which possesses them. To this question it is sufficient 

 to answer that they are useful in effecting or preserving 

 segregation, without which the species, as a distinct species, 

 would cease to exist. We are not at present concerned 

 with the question whether divergence in itself is useful or 

 advantageous. If it be pressed, we must reply that, although 

 divergence is undoubtedly of immense advantage to life in 

 general, enabling, as Darwin said, its varying and diver- 

 gent forms to become adapted to many and highly diversified 

 places in the economy of nature, still in many individual 

 cases it is neither possible nor in any respect necessary to 

 our conception of evolution to assign any grounds of utility 

 or advantage for the divergence itself. 



In any case, we are dealing at present with the utility 

 of specific characters to the species which possess them ; 

 and under the head of utility we are including usefulness 

 in effecting or maintaining segregation. Now, we have 

 already seen that variations may be either advantageous 

 (useful), or neutral (useless), or disadvantageous (worse 

 than useless). The latter class we may here disregard; 

 elimination will more or less speedily dispose of them. 

 With regard to neutral (useless) variations, we must also 

 note that they may be correlated with variations of the 

 other two classes. If correlated with disadvantageous 

 variations, they will be eliminated along with them; if 

 correlated with advantageous variations, they will escape 

 elimination (or will be selected) together with them. There 

 remain neutral, or useless, variations, not correlated with 

 either of the other two classes. Are these in any cases 

 distinctive of species ? 



It is characteristic of specific distinctions that they are 

 relatively constant. Elimination, selection, or preferential 

 breeding gives them relative fixity. On the other hand, it 

 is characteristic of neutral variations that they are incon- 

 stant. There is nothing to give them fixity. It is, of 

 course, conceivable that all the migrants to a new area 

 were possessed of a useless neutral character, which those 

 in the mother area did not possess ; or that such a useless 



