134 W. H. BURT 



possibility of climatic change and the accompanying changes in 

 flora. These changes, if they occurred, would have influenced not 

 only distribution patterns but also population densities. 



3. The Area of Greatest Diver sificatioyi {at present) of the Group 

 Is Likely the Place Where It Evolved into Its Present Phase. Some 

 authors have thought that the area now supporting the greatest 

 number of species (of a genus) must be the area where the group 

 reached its present evolutionary phase; that far from the place 

 where they evolved, individuals of a species are less plastic and 

 less able to adapt to diversified conditions. However, this does not 

 necessarily follow. It is usual to find diversity in a group (a genus, 

 for example) in an area that supports many kinds of habitats, 

 where ecological conditions are diverse. If these diverse ecological 

 conditions have persisted over a long period of time in the same 

 area, it is conceivable that many of the lower categories and, given 

 enough time, the higher categories might have developed there. 

 But, especially for the larger categories, this is problematical. 

 They might or might not have evolved in the area. 



4. The Area Where Individuals Show the Highest Development, 

 Are Least Primitive, Is Probably the Place of Differentiation of the 

 Group. This is in keeping with Matthew's hypothesis. It is more 

 likely to hold for the higher categories (families and orders) than 

 for the lower ones. Without the fossil record, the same objections 

 apply to this as to other hypotheses. 



5. Ecological Tolerance. Some authors have held that if a 

 species can adapt to several kinds of habitat, if it is not confined to 

 narrow ecological conditions, it still maintains a certain plasticity 

 and some of its initial potential for adaptation. Therefore, this 

 area, where the species is adaptable, is likely to be at or near the 

 place where it evolved from its ancestral stock. This, of course, 

 need not be true. 



These are some of the ideas that have been expressed by students 

 of Recent biota. (For others, and a critique of them, see Cain, 

 1944; Darlington, 1957, pp. 29-35). They are all indirect lines of 

 evidence, but they may be used to advantage where other evidence 

 is not available. If any one of the above criteria is used, it should 

 be applied with extreme caution, because it may or may not lead 

 to a true interpretation of the facts. Darlington (1957, p. 580) 

 goes so far as to state: "I doubt whether any existing animals tell 



