154 THE LESSON OF EVOLUTION 



The fact is that one pattern is as useful as the other,, 

 neither more nor less ; and as no advantage is gained 

 by having different patterns, they cannot have been 

 developed by natural selection. 



I am tempted to give one more illustration, taken 

 from the class of birds. 



There is a genus of small fruit-pigeons, called 

 Ptilonopus, found in the Malay Archipelago and 

 Polynesia. It contains twenty-three species, of 

 which no fewer than thirteen are found, isolated 

 from other species of the genus, each in its own 

 island or small group of islands ; the other ten 

 living associated, two or more species together. 

 Now it is highly improbable that the whole of the 

 thirteen isolated species were developed on other 

 islands from which they have migrated, and that 

 their ancestors, who were left behind, have all be- 

 come extinct in their former homes. Also, it is- 

 highly improbable that formerly two or more species 

 of Ptilonopus existed on each of these thirteen 

 islands, and that all have been destroyed except one 

 species in each island. Either one or other of 

 these cases might happen occasionally ; but it is 

 impossible that thirteen should occur simul- 

 taneously. Consequently, it appears certain that 

 most of these species were developed singly, each 

 on its own island. If this be the case, the colours 

 which now distinguish the different species 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 corre- 

 lation, because they are the only characters which 



