710 



THE ORIGIN OF SPECIES 



not, as Darwin himself recognised, incompatible with creation, 

 but it puts the necessity for creation further back in time and 

 reduces the number of creative acts which are necessary. It 

 therefore enables men to forget the origins of things in directing 

 their attention to more recent happenings. We must now consider 

 the sort of evidence which convinced people that evolution was 

 a reasonable hypothesis, and then the mechanism by which it 

 may be supposed to have come about. 



I. The only direct evidence for evolution would be to see it 

 in action. There can be little doubt that new species of plant 

 have arisen in historic times, but we have no similar evidence 

 for animals. We do know, however, instances where the form of 

 a species has changed. The normal form of the peppered moth, 



Fig. 545.- 



-Amphidasis hetularia. A normal female below, a melanic female 

 above. — After Lemche. 



Biston [=Amphidasis) hetularia (Fig. 545), has mottled wings, but 

 in 1850 a dark and uniformly coloured variety, later called 

 carhonaria, was discovered in Manchester. This melanic type 

 spread, slowly at first, until by 1910 it was, in the industrial north, 

 present in equal numbers with the normal form. By 1950 there 

 were hardly any of the normal form in the industrial north, while 

 in the rest of England carhonaria was spreading more slowly. The 

 dark type might be considered as a subspecies, and it is not 

 unreasonable to think of subspecies as incipient species. 



2. Parallel with a few observations which have been made 

 in nature on the change of form of animals are the many on the 

 changes which occur under domestication. The actual origin of 

 most of our domestic animals goes back to the obscurity of pre- 



