178 THE WORLD OF LIFE 



the emerald is no better in the battle of life than a frill ending 

 in spangles of the ruby. A tail is not affected for the purpose of 

 flight, whether its marginal or its central feathers are decorated 

 with white. . . . Mere beauty and mere variety, for their own 

 sake, are objects w^hich we ourselves seek when we can make the 

 forces of nature subordinate to the attainment of them. There 

 seems to be no conceivable reason why we should doubt or question 

 that these are ends and aims also in the forms given to living or- 

 ganisms." 



In a criticism of the Duke's book (written in 1867) I 

 adduced sexual preference by the female bird as sufficiently 

 explaining these varieties of plumage and colour, but I have 

 since come to doubt the validity of this, except so far as the 

 plumes are an indication of sexual maturity; while I see in 

 the need for outward marking, whether for purposes of recog- 

 nition or as preventing intercrossing between incipient species, 

 a sufficient cause for all such conspicuous indications of 

 specific diversity as are found perv^ading the whole vast world 

 of life. It now only remains to point out how these mark- 

 ings have been produced, even under conditions which some 

 writers have considered must render their production for this 

 purpose impossible, and therefore as constituting a valid ob- 

 jection to the whole theory of recognition-marks. 



An Objection to Recognition-Marhs answered 



In a book on Darwinism and Lamarckism, the late Captain 

 Hutton, a well-known Kew Zealand naturalist, objected to the 

 validity of recognition-marks as a cause for the development 

 of specific characters, that there are, all over the Pacific, 

 numerous cases of small fruit-pigeons of the genus Ptilopus, 

 which each have distinctive markings, and are almost always 

 confined to one island or a small group of islands. In most 

 of these cases there is no other pigeon or other bird on the 

 same island for which they could possibly be mistaken. He 

 then says : 



