2O Darwin, and after Darwin. 



have been lost to observation. And this possibility 

 becomes little less than a certainty when we note the 

 next consideration which I have to adduce, namely, 

 that in all their systematic divisions of plants and 

 animals in groups higher than species such as genera, 

 families, orders, and the rest naturalists have at all 

 times recognised the fact that the one shades off into 

 the other by such imperceptible gradations, that it 

 is impossible to regard such divisions as other than 

 conventional. It is important to remember that this 

 fact was fully recognised before the days of Darwin. 

 In those days the scientifically orthodox doctrine 

 was, that although species were to be regarded as 

 fixed units, bearing the stamp of a special creation, 

 all the higher taxonomic divisions were to be con- 

 sidered as what may be termed the artificial creation 

 of naturalists themselves. In other words, it was 

 believed, and in many cases known, that if we could 

 go far enough back in the history of the earth, we 

 should everywhere find a tendency to mutual ap- 

 proximation between allied groups of species ; so that, 

 for instance, birds and reptiles would be found to be 

 drawing nearer and nearer together, until eventually 

 they would seem to become fused in a single type; 

 that the existing distinctions between herbivorous 

 and carnivorous mammals would be found to do like- 

 wise ; and so on with all the larger group-distinctions, 

 at any rate within the limits of the same sub-kingdoms. 

 But although naturalists recognised this even in the 

 pre-Darwinian days, they stoutly believed that a 

 great exception was to be made in the case of species. 

 These, the lowest or initial members of their taxo- 

 nomic series, they supposed to be permanent the 



