no Animal Life and Intelligence. 



remarkably subject to variation, as may be well seen in the 

 case of ruffs (Machetes pugnax) in the British Natural 

 History Museum. In the case of our two islands with 

 isolated faunas, therefore, if they formed separate breeding- 

 areas for birds, the chances would be many to one against 

 the change in the standard of recognition -marks being 

 identical in each area. Hence might arise those minute 

 but definite specific distinctions which are so noteworthy 

 in this class of the animal kingdom. Instance the Old and 

 New World species of teal, the Eastern and Western species 

 of curlew and whimbrel, and other cases numerous.* This, 

 in fact, is probably in many cases the true explanation of 

 the occurrence of representative species, slight specific 

 variations of the same form as it is traced across a conti- 

 nent or through an archipelago of islands. 



The question has been raised, and of late a good deal 

 discussed, whether specific characters, those traits by 

 which species are distinguishable, are always of use to the 

 species which possess them. Here it is essential to define 

 what is meant by utility. Characters may be of use in 

 enabling the possessor to resist elimination ; or, like the 

 colours of flowers, they may be of use in attracting insects, 

 and thus furthering selection ; or, like recognition-marks, 

 they may be of use in effecting segregation. This last form 

 of utility is apt to be overlooked or lost sight of. In speak- 

 ing of humming-birds, the Duke of Argyll says that " a crest 

 of topaz is no better in the struggle for existence than a 

 crest of sapphire. A frill ending in spangles of the emerald 

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

 spangles of the ruby." But if these characters be recog- 

 nition-marks, they may be of use in segregation. They are 

 a factor in isolation. But it may be further asked — What 

 is the use of the segregation ? Wherein lies the utility of 

 the divergence into two forms ? This question, however, 

 involves a complete change of view-point. The question 

 before us is whether specific characters are of Use to the 



* See " Evolution -without Natural Selection," by Charles Dixon. This 

 author's facts are valuable ; his theories are ill digested. 



