MR. G. J. EOMANES ON PHYSIOLOGICAL SELECTIOK. 345 



of innumerable structures and instincts whicli for the most 

 part are of generic, family, or higher order of taxonomic value. 

 Therefore, unless we reason in a circle, it is not competent to 

 argue that the apparently useless structures ^and instincts of 

 specific value are due to some kind of utility which we are unable 

 to perceive. But I need not argue this point, because in the 

 later editions of his works Mr. Darwin freely acknowledges that 

 a large proportion of specific distinctions must be conceded to 

 be useless to the species presenting them ; and, therefore, that 

 they resemble the great and general distinction of mutual sterility 

 in not admitting of any explanation by the theory of natural 

 selection. 



Natueal Selection not a Theory oe the 

 Origin op Species. 



In view of the foregoing considerations it appears to me obvious 

 that the theory of natural selection has been misnamed ; it is 

 not, strictly speaking, a theory of the origin of species : it is a 

 theory of the origin — or rather of the cumulative development 

 — of «^ap^a^^o?^s, whether these be morphological, physiological, 

 or psychological, and whether they occur in species only, or like- 

 wise in genera, families, orders, and classes. These two things 

 are very far from being the same ; for, on the one hand, in an 

 enormously preponderating number of instances, adaptive struc- 

 tures are common to numerous species ; while, on the other 

 hand, the features which serve to distinguish species from species 

 are, as we have just seen, by no means invariably — or even 

 generally — of any adaptive character. Of course, if this were 

 not so, or if species always and only difi^ered from one another in 

 respect of features presenting some utility, then any theory of 

 the origin of such adaptive features would also become a theory 

 of the origin of the species which present them. As the case 

 actually stands, however, not only are specific distinctions very 

 often of no utilitarian meaning ; but, as already pointed out, the 

 most constant of all such distinctions is that of sterility, and this 

 the theory of natural selection is confessedly unable to explain. 



Eor these reasons I think there can be no doubt that the 

 theory of natural selection ought to be recognized as exclusively 

 a theory of the evolution of adaptive modifications ; not there- 

 fore or necessarily a theory of the evolution of different species. 

 And, if once this important distinction is clearly perceived, the 



