380 STUDIES, SCIENTIFIC AND SOCIAL chap. 



marking, no peculiarities of instinct or of habit, no rela- 

 tions between species or between groups of species, can 

 exist but which must now be, or once have been, useful to 

 the individuals or races which possess them." Professor 

 Huxley, in his obituary notice of Darwin, expressed the 

 same idea as follows : — " Every variety which is selected 

 into a species is favoured and preserved in consequence of 

 being, in some one or more respects, better adapted to its 

 surroundings than its rivals. . . . For, as has been pointed 

 out, it is a necessary consequence of the theory of Selection 

 that every species must have some one or more structural 

 or functional peculiarities, in virtue of the advantage con- 

 ferred by which it has fought through the crowd of its 

 competitors and achieved a certain duration. In this 

 sense it is true that every species has been ' originated by 

 selection.' " Now these characters, in virtue of which the 

 variety has become a species, are in fact its " specific 

 characters," and they alone will absolutely ditferentiate it 

 from all other species. We need not trouble ourselves 

 about the cases of doubtful species, in which the distinctive 

 characters are either so minute or so unstable that we 

 cannot invariably determine them. On the theory of 

 evolution by natural selection there must be such cases. 

 They are species in the making and not quite completed. 

 But in the great majority of species definite characters do 

 exist by which any single individual can be recognised 

 and the species to which it belongs be determined ; and 

 the question is, whether or no the characters, or combin- 

 ation of characters, which thus differentiate it are now 

 useful or were useful at the time of its origination.^ In 

 order to answer this question, we must briefly summarise 

 both the facts and the admitted principles or theories 

 which bear upon it. 



^ To this should Le added — "or were correlated with some useful 

 characters." I have referred to such correlations in my Natural 

 Selection and Tropical Nature, pp. 172 and 175 ; and as to apparently 

 useless characters being in some cases correlated with those which are 

 useful, in my Darwini.wi, p. 140 ; but it is cumbersome to restate tliis 

 part of the theory whenever it is alleged that all specific characters 

 are useful. 



