ca.pt. f. w. hdtton" on the problem of utility. 333 



are found isolated from other species of the section, each on its 

 own island or small group of islands. Now it is highly improbable 

 that all these thirteen species were developed on other islands 

 on which they are no longer found ; or that other species of the 

 section Ptilopus formerly lived on each, of these thirteen islands 

 and have become extinct on them. If it had been a single case 

 only, we might have had some doubt ; but when it comes to 

 having to apply the same explanation to more than half of the 

 whole number of species, it seems to me to be absurd. Conse- 

 quently it appears almost certain that most of these species were 

 developed each on its own island ; and, this being allowed, we 

 have tlie problem of the origin of their specific characters reduced 

 to its simplest form. 



If these species originated in the islands in which they are 

 found, the colours which distinguish them cannot be recognition- 

 marks, because there is no other species in each island with which 

 they could be confounded. The colours cannot be due to cor- 

 relation, because they are the only characters which have changed. 

 They cannot have been useful to ancestors, because they have 

 only lately been developed. And we cannot suppose that they 

 give any special advantage in each island, because all the islands 

 have practically the same climate and the same flora and fauna. 

 This exhausts the resources of the principle of utility, and we are 

 driven to the conclusion that these specific characters have a non- 

 utilitarian origin ; and yet they are found " in every individual 

 constituting the species, neither more nor less." 



I therefore submit that, whether we can discover the cause or 

 not, there is an overwhelming probability in favour of the state- 

 ment that these truly specific characters have had a non-utilitarian 

 origin ; and if the specific colours have not had a utilitarian 

 origin in these cases, it is quite probable that they may not have 

 had a utilitarian origin in other cases where two or more species 

 of the section are found in the same island ; and it follows that 

 recognition- marks do not necessarily arise through selection. 

 Indeed, there appears to be no reason why even adaptations 

 should not arise by the same non-utilitarian process ; although, 



and Eaiatea, Society Islands ; P. coralensis, in Carlsoff Island, Paumotu 

 Group ; P. Smithsonianus, some island, Paumotu Group ; P. Tristrami, in 

 Hivaoa, Marquesas Group ; and P. Ruttoni, in Rapa, S.E. of the Austral 

 Islands. Further knowledge is more likely to increase than to diminish 

 this list. 



