398 STUDIES, SCIENTIFIC AND SOCIAL ch. xviii 



extension to any of the varieties which are destined to 

 become new species. Unless the power in question can 

 have this twofold effect it cannot lead, except by accident, 

 to the production of useless specific characters. 



Under conceivable conditions, however, it is possible 

 that certain useless characteristics may become limited to 

 the individuals of a single species. But what we know of 

 the modes of variation and the distribution of varieties 

 indicates that, if at any time so produced, they must be 

 altogether exceptional and of the nature of chance 

 products ; and that they cannot possibly constitute such a 

 general characteristic of species as has been suggested. 



Our final conclusion is that, whether we can discover 

 their use or no, there is an overwhelming probability in 

 favour of the statement that every truly specific character 

 is or has been useful, or, if not itself useful, is or has 

 been strictly correlated with some useful character. 



