394 ME. a. J. EOMANES ON PHYSIOLOGICAL SELECTION. 



•wMcli present no utilitarian significance. And, as previously 

 argued, it is impossible to believe that there can be any general 

 or constant correlation between disguised utility and insignifi- 

 cance of secondary distinction. 



Now, the large body of facts to which I here allude, but will 

 not at present wait to specify, appear to me to constittxte 

 perhaps the strongest of all my arguments in favour of physio- 

 logical selection. Take, for instance, a large continental area 

 and follow across it a cbain of species, each link of which differs 

 from those on either side of it by the most minute and trivial 

 distinctions of a secondary kind, but all the links of which differ 

 from one another in respect of their reproductive systems, so 

 that no one member of the series is perfectly fertile with any other 

 member. Can it be supposed that in every case this constant 

 primary distinction has been superinduced by the trivial secon- 

 dary distinctions, distributed as they are over different parts of 

 all these kindred organisms, and yet nowhere presenting any 

 but the most trifling amount of morphological change ? Or, 

 even if we were to suppose this, we have still to meet the 

 question. How were all these trifling changes produced in the 

 face of free intercrossing on the continuous area? Certainly 

 not by natural selection, seeing that they are useless to the 

 species presenting them. Let it then be by changes in the con- 

 ditions of life, whether of food, of climate, or of any thing else. 

 I can conceive of no other alternative. Yet if we accept this 

 alternative, we are but espousing — in a disguised and roundabout 

 way to be sure — the theory of physiological selection. For we 

 are thus but hypothetically assigning the causes which have in- 

 duced the primary distinction in each case, or the causes which 

 have led to the mutual sterility. For my own part, I believe 

 that the assignation would be, in the great majority of such cases, 

 incorrect. That is to say, for reasons already given, I do not 

 believe that in the great majority of such cases the trivial se- 

 condary distinctions, howsoever these were caused, can have 

 had any thing to do with the great primary distinction. What 

 I believe is, that all the closely allied species inhabiting our sup- 

 posed continent, and differing from one another in so many points 

 of minute detail, are but so many records of one particular kind 

 of variation having taken place in the reproductive systems 

 of their ancestors, and so often as it did take place, having 

 necessarily given birth to a new species. The primary distinc- 



