Variation and Naticral Selection, 103 



migrate together. Mr. Wallace considers that they " have 

 in all probability been acquired in the process of differentia- 

 tion for the purpose of checking the intercrossing of allied 

 forms ; " for " one of the first needs of a new species would 

 be to keep separate from its nearest allies, and this could 

 be more readily done by some easily seen external mark 

 of difference." This language seems, however, to savour 

 of teleology (that pitfall of the evolutionist). The cart is 

 placed before the horse. The recognition-marks were, I 

 believe, not produced to prevent intercrossing, but inter- 

 crossing has been prevented because of preferential mating 

 between individuals possessing special recognition-marks. 

 To miss this point is to miss an important segregation- 

 factor. Undoubtedly, other tendencies co-operate in main- 

 taining the standard of the recognition-marks. Stragglers 

 who failed in the matter of recognition would get separated 

 from their fellows, and stand a greater chance of elimi- 

 nation by enemies ; young who failed in this respect would 

 be in like condemnation. Still, I cannot doubt that the 

 foundations of recognition-marks were laid in preferential 

 mating, and that in this we have an important factor in 

 segregation. 



We may here note, in passing, as also arising out of 

 preference, how the selection of flowers by insects may 

 lead to segregation ; for insects seem often to have habitual 

 or instinctive colour-preferences. Flowers of similar colour 

 would be thus cross-fertilized, but would not intercross with 

 those of different colour, whence colour-varieties might 

 arise. It is important to note that in these cases there is 

 a psychological factor in evolution. 



We have so far assumed that intercrossing of parents 

 and interblending of their characters in the offspring 

 always go together. This, we must now notice, is not 

 always the fact. If a blue-eyed Saxon marry a dark-eyed 

 Italian, the children will have blue eyes or dark eyes, not 

 eyes of an intermediate tint. The characters do not inter- 

 blend. The ancouy or otter-sheep, a breed with a long 

 body and short, bandy legs, appeared in Massachusetts as 



