446 SCIENCE PROGRESS 



York, concludes that while fourteen of these species are the 

 result of specific or generic instability (i.e. recent mutations), 

 two have arisen by adaptation of wider spread species to the 

 local environment, and only five by the dying out of previously 

 more widely distributed species. 



The mutation controversy is involved, but at present only 

 one contributor, Ridley (7), has attempted to uphold the 

 theory of natural selection to the exclusion of mutations. 

 Ridley criticises the age and area hypothesis on various grounds. 

 He takes the very common species of Willis and Trimen to 

 mean species which are abundantly represented by individuals 

 instead of species which are widespread, and gives various 

 cases of such locally abundant species which have died out 

 in particular localities, especially as the result of the advent 

 of man. He claims also to prove that these species may dis- 

 appear without a geological catastrophe. As he quotes vol- 

 canic action and the glacial period as non-catastrophic occur- 

 rences, it is difficult to follow his argument. It is also difficult 

 to understand what Mr. Ridley thinks of the case for muta- 

 tions as he states in his summary that " the mutation theory 

 ... is not in accordance with the facts," while in the text 

 of the paper he gives a very good account of the action 

 of natural selection in killing out injurious " mutations " and 

 of the origin of species by mutation. " This theory," he says, 

 " can be tested and proved by the study of mutations." He 

 proceeds, moreover, to quote well-developed spines, a change 

 in stature from about 6 in. to about 10 ft., etc., as " one or 

 two examples of infinitesimal variations." 



Willis has replied in a recent paper (18) by acknowledging 

 that the action of man and other subsidiary causes may 

 modify the action of the law of age and area. " Mr. Ridley 

 quotes about seventy cases in various connections. Many of 

 these, e.g. those on p. 555, are excellent illustrations of what I 

 have said (16, p. 22) that a very small accident may kill out 

 a species in the class VR." " VR " means very rare, and 

 among the cases mentioned is that of Didymocarpus Perdita, 

 Ridley. The note on this species by Ridley is, " I found two 

 plants of this on a bank in the centre of Singapore surrounded 

 by extensive cultivation. It has never been seen again." It 

 seems not impossible that the description of this species by its 

 author involved its destruction, an excellent example for the 



