1 92 1.] Suhspecies and Evolution. 537 



5. Definition of a subspecies. 



There can be no hard-and-fast definition for a state of 

 nature which is constantly changing. There exist forms 

 which we all know, whose status is still unsatisfactory, and 

 even Nature herself might have difficulty in defining them 

 as species or subspecies, for the simple reason that they are 

 in the transitional stage betweon the two. 



But it seems correct to describe trinomially as geo- 

 graphical races those birds of similar type inhabiting 

 different geographical areas, and whose differences are 

 abundantly (not exclusively) constant within a given area. 

 In fact, they must be a pure geographical variation, the 

 variation coinciding with distribution. 



Intermediate forms will nearly always be found in inter- 

 mediate areas, but such need not always be the case, as in 

 the instance of a race which has receded from its parent 

 stock into temporary isolation, and which has again ex- 

 panded towards its parent stock. Such appears to be the 

 case with Corvus f. frugilegus and Corvus f. pastinator, and 

 perhaps with Erolia miuuta a-nd Erolia rujicollis. Opinion is 

 bound to differ regarding the status of such forms, as the 

 question is a pure matter of opinion and not of fact. 



Again, it is frequently stated that two geographical races 

 of the same species must not breed in the same area. We 

 agree that a geographical race is destroyed if another race 

 of the same species continually breeds over a wide area of 

 the former ; but where two races of the same bird meet, they 

 naturally, either by mating together or under the influence 

 of intermediate conditions, produce intermediate forms. In 

 fact, where this occurs it is good proof of the two races 

 being good geographical races of the same species. 



This short article is not intended to be a treatise on 

 evolution. It has been written in the hopes that it may 

 form the basis of a discussion in which we may have the 

 opportunity to take part at some future meeting of the 

 British Ornithologists' Club. To the highly-trained scientific 

 mind, many of my contentions are no doubt ridiculous and 

 untenable. It is the truth we seek, and if from the fallacies 

 in my arguments others can point to more truthful causes of 

 evolution, my time will not have been wasted. 



2n2 



