MR. G. J. ROMANES ON PHYSIOLOGICAL SELECTION. 347 



case of specific distinctions ? Surely because some cause other 

 than natural selection must have been at work in the differen- 

 tiation of species, which has operated in a lesser degree in the 

 differentiation of genera, and probably not at all in the differen- 

 tiation of families, orders, and classes. Such, a cause it is the 

 object of the present paper to suggest ; and if in the foregoing 

 preamble it aj)pears somewhat presumptuous to have insinuated 

 that Mr. Darwin's great work on the ' Origin of Species ' has 

 been misnamed, I will conclude the preamble with a quotation 

 from that work itself, which appears at once to justify the in- 

 sinuation, and to concede all that I require. 



" Thus, as I am inclined to believe, morphological difi"erences, 

 which we consider as important, such as the arrangement of the 

 leaves, the division of the flower or of the ovarium, the position 

 of the ovules, &c., first appeared in many cases as fluctuating 

 variations, which sooner or later became constant through the 

 nature of the organism and of the surrounding conditions, as 

 well as through the intercrossing of distinct individuals ; but 

 not through natural selection ; for as these morphological cha- 

 racters do not affect the welfare of the species, any slight varia- 

 tions in them could not have been governed or accumulated 

 through this latter agency. It is a strange result which we thus 

 arrive at, namely that characters of slight vital importance to 

 the species are the most important to the systematist "*. 



* ' Origin of Species,' ed. 6, p. 176. See also p. 365 et seq. The argument is 

 that the guiding principle of classiiication being a hitherto unconscious tracing 

 of the lines of genetic descent, and heyedity not being more concerned with pre- 

 serving useful variations than indifferent ancestral peculiarities, the latter are 

 now of more use than the former to systematists, seeing that they have been 

 allowed to persist without undergoing adaptive modification at the hands of 

 natural selection. I have no doubt that this argument is sound; but the 

 " strange result " to which it leads implies that natural selection has throughout 

 been the cause of the origin of adaptations ; not therefore necessarily, or even 

 generally, of the origin of species. But let me not be misunderstood. In 

 saying that the theory of natural selection is not, properly speaking, a theory 

 of the origin of species, I do not mean to say that the theory has no part at 

 all in explaining such origin. Any such statement would be in the last degree 

 absurd. What I mean to say is that the theory is one which explains the 

 origin or the conservation of adaptations, whether structural or instinctive, 

 and whether these occur in species, genera, families, orders, or classes. In so 

 far, therefore, as useful structures are likewise species-distinguishing structures, 

 so far is the theory of their oi'igin also a theory of the origin of the species 

 which present them. But useful structures and species-distinguishing struc- 



