140 TEST CASES [ch. xii 



where described (p. 57) — can be difficult of acquisition. In 

 many cases differences of this kind can be seen between closely 

 related species. The only reasonable explanation is that their 

 appearance has nothing directly to do with adaptation, and is the 

 result of simple mutation, which is so very commonly divergent. 

 In other words, this phenomenon, which is so very common 

 throughout the vegetable kingdom, and which is not unknown in 

 the animal, is an expression of the operations of differentiation, 

 not of those of natural selection, while at the same time it 

 suggests complications in evolution, perhaps like those suggested 

 by Hayata (16). 



TEST CASE XXV. GREATER LOCALISATION 

 OF HIGHER TYPES 



That the higher groups of organisms, for example the flowering 

 plants, are more localised in distribution than the lower groups, 

 such as the ferns, has long been an accepted axiom, and has often 

 been put down, as for example by Darwin and by the author, 

 largely to the greater antiquity of the lower groups. But if we 

 carry this principle into greater detail, it is clear that if in any 

 family or group of families some forms are more widely distri- 

 buted than others, those forms should on the whole be the older 

 — the principle for which the author contended in the hypothesis 

 of age and area. But the explanation of geographical distribu- 

 tion that is given by natural selection, or gradual structural 

 adaptation, involves the assumption that the forms that have 

 spread the most widely will be those that are the best adapted, 

 though to what they are adapted is left vague. Upon this view of 

 evolution, one cannot regard genera like Carex, Draba, Eryngium, 

 Eugenia, Eujjhorbia or Senecio as being poorly adapted when 

 compared with the vastly more numerous smaller and more 

 localised genera. But when one asks why such families as Cepha- 

 lotaceae, Hydnoraceae, Nepenthaceae, Orobanchaceae, or Sar- 

 raceniaceae have not spread widely, with such "adaptations" 

 as they show, one is told that their adaptation is too special to 

 have allowed them to do so. But why should Nepenthes, for 

 example, be well suited to the variety of conditions with which it 

 meets in Malaya, Ceylon and Madagascar, and yet not capable of 

 withstanding those of tropical Africa, America, Polynesia or 

 Australia? The Sarraceniaceae, with not dissimilar adaptations, 

 can do so, and do not occur in the Old World. It is not even as if 

 there were only one species in each of the genera ; there are scores 



