GEOBGE JOHN KOMANES issi- 



sense of life-preserving. On the contrary, in most 

 cases such structures entail considerable expenditure 

 of physiological energy in their production. On this 

 account Darwin says that nat. sel. must impose a 

 check on sexual selection running beyond a certain 

 point of injuriousness (' D. of M.,' p. 227). Now, 

 physiological selection is never thus injurious ; and 

 although it is a 'form of isolation,' the isolation is 

 neither so extreme nor of such long continuance as 

 the ones you compare it with. Moreover, the environ- 

 ment (therefore all other or external conditions of life) 

 remains the same, which is not the case under the 

 other forms of isolation. Provided that the physio- 

 logical change is not in itself injurious, I do not see 

 why physiologically isolated forms should be less fit 

 than those from which they have been separated, 

 though I can very well see why this should be the 

 case with such geographically isolated forms as you 

 mention, for there the schooling is different. Lastly, 

 physiological selection, if not in itself injurious, does 

 not require that its children should be ' protected 

 against the struggle for existence.' On the contrary, 

 as I say in my paper, it is calculated to give this 

 struggle a better chance than ever to develope adap- 

 tive character in the sexually isolated forms, because 

 the swamping effects of intercrossing are diminished. 

 But I really did not intend to afflict you with 

 another jaw of this kind. I am, however, very glad 

 that we now understand each other better than we 

 did. At all events on my side I think I now know 

 exactly the points which I have to make good if 

 Nature is so constituted as to admit of my theory. 



