46 CONTACTS WITH DARWINISM III [ch. v 



largest genus in the family, but it is the most widespread, and 

 when these two characters do not agree in pointing out what is 

 probably the oldest genus, the author considers that distribution 

 rather than size should be regarded as more important. 



In thus supposing that a genus could appear at one stroke, and 

 that one genus could, directly, give rise to another, the author 

 was definitely going beyond mutation pure and simple, and 

 adopting the theory of differentiation, in which, as the changes 

 were large, the idea that the morphological differences represented 

 adaptational improvements was discarded. In other words, 

 though evolution was unquestionably going on, and was on the 

 whole, though more notably in the animal world, producing 

 higher and higher types, there was no need to suppose that there 

 was necessarily any adaptational reason in the innumerable 

 structural changes that showed themselves in the course of that 

 evolution, and indeed showed that evolution was going on at all. 

 It seemed much more probable that most of those features which 

 we were accustomed to call adaptational improvements had 

 appeared already full-fledged. If new features that thus appeared 

 were really harmful, or met with ill-luck, they were promptly 

 removed by the action of natural selection. If they were bene- 

 ficial, or not harmful, and met with average luck, they were 

 retained. 



The sketch showed the way in which it was suggested that 

 evolution had proceeded, from the large and widespread genera 

 down to the small and local, but there was then about as much 

 chance to prove this kind of mutation as to prove that natural 

 selection could do what was required to form a new species, for 

 it must not be forgotten that this has not yet been done. There is 

 some reason to suppose that it can produce new varieties, but 

 no proof that it can cross the line of mutual sterility that usually 

 lies between species. Both theories derive varieties from a parent 

 species, but selection derives them from a parent which is at an 

 earlier stage of development, and perhaps fated to die out, the 

 varieties being considered as on the way to species. Differentia- 

 tion does not admit this, but regards them as later stages of 

 development by mutation than the species that gave rise to 

 them, and with which they are not necessarily in competition, 

 though perhaps they may sometimes go on, by further mutation, 

 to become new species. The essential point at present, for dif- 

 ferentiation, is to prove that evolution proceeded in the direction 

 from family to species, and not the reverse. 



