256 I The Process of Evolution 



considerable genetic variability. Pinus radiata has suffered range 

 reduction in recent times and perhaps would be on the road to 

 extinction were it not for the fact that the tree is much cultivated and 

 has been introduced into many parts of the world where it is grown 

 for paper pulp manufacture. 



The situations just described, where a species or small group of 

 species appears to be very distinct from other such groups, all in- 

 volve extinction. The group is distinct because closely related forms 

 have not survived. When the fossil record is considered (if such is 

 available), the distinctness of the species disappears. Similar mis- 

 conceptions result when forms living in a rather broad geographic 

 area are studied in only a part of their range. Distinct clusters seem 

 to be present when a limited geographic area is considered, but when 

 the world picture is studied, this conclusion no longer obtains. As 

 with the previous examples, the problem is one of sampling, in this 

 instance insuflBcient sampling in space rather than insufficient 

 sampling in time. 



Biogeographic Provincialism 



In North America, there are four distinct kinds of animals included 

 in the butterfly genus Nijmphalis (N. antiopa, N. milberti, N. cali- 

 fornica, and N. vati-album) . Individuals may be assigned to one of 

 the four forms with certainty, no intermediates having been dis- 

 covered. When Nijmphalis of the Palearctic region are considered 

 as well, the impression of neat packages disappears. The relationship 

 of the cluster that we call N. vau-album to the Eurasian form of 

 the same name is open to some question. In the few characters 

 studied (size, color pattern, genitalia) in samples from North 

 America and Eurasia there is considerable overlap in variation. As 

 in most other cases, an estimate of the actual degree of differentia- 

 tion must await thorough studies of large samples of characters. 

 Similarly, the amount of differentiation between N. milberti and 

 the Palearctic members of the N. urticae complex (Fig. 11.3) and 

 among N. californica and the Old World IV. polychloros and N. 

 xanthomelas needs further investigation. There are myriad similar 

 situations. 



In Yellowstone National Park there are two kinds of bears: black 

 bears (Ursus americanus) and grizzly bears {U. horribilis) . If the 

 Park were the entire range of the grizzly, then grizzly bears would 

 form a distinct apparently uniform cluster of the same sort as was 

 described for the tuatara (Sphenodon) . However, the grizzly ranges 

 northward to Alaska, where populations are made up of very large 



