164 GEOEGE JOHN EOMANES I88I- 



origin and cumulative development of adaptations, 

 whether these be distinctive of species, or of genera, 

 families, classes, &c. 



The question then arises, do species differ from 

 species solely in points of a useful character, as they 

 undoubtedly should do if natural selection has been 

 the sole factor in their formation ? Investigation 

 shows that systematists recognise a species by a 

 collection of characters, the value of a character 

 depending not on its utility, but upon its stability ; 

 in fact, a large proportional number of specific cha- 

 racters, such as minute details of structure, form, and 

 colour, are wholly without meaning from a utilitarian 

 point of view. Investigation further shows that the 

 most general of all the ' notes ' of a true species is 

 cross-infertility, that is, the infertility of the offspring 

 of two individuals belonging to separate species : 

 this, it was urged, could not be due to the action of 

 natural selection. Lastly, apart from the primary 

 distinction of cross-infertility, and the inutility of so 

 many of the secondary specific distinctions, neither 

 of which can be explained by the action of natural 

 selection, Mr. Romanes was strongly of the opinion that 

 even if a beneficial variation did arise, the swamping 

 effects of free intercrossing would reabsorb it, and so 

 render evolution of species in divergent lines, as 

 distinguished from linear transmutation, impossible. 

 This last difficulty can only be met by assuming that 

 the same beneficial variation arises in a number of 

 individuals simultaneously, for which assumption 

 our present knowledge furnishes no warrant. If 

 natural selection is brought forward as the sole factor 

 in the guidance of organic evolution, then he con- 

 sidered that these difficulties remain insurmount- 

 able ; if, however, it is regarded as a factor, even the 

 chief factor, then these difficulties vanish, it being 

 consistent, in the latter case, to hold the other 



