Major Patterns of Variation | 257 



individuals (Alaska brown bears, U. middendorffi) and thence into 

 Eurasia {U. arctos). It seems likely that these bears form an inter- 

 grading series of clusters. The polar bear {U. tnaritimiis) is a very 

 closely related cluster adjusted primarily to marine life in the 

 Arctic. The brown and polar bears are largely allopatric, although 

 occasional individuals meet along the Arctic coast. To our knowl- 

 edge, intermediate individuals have not been reported in nature 

 (although zoo hybrids are well known). Thus, although bear tax- 

 onomy might seem simple to the inhabitant of Yellowstone Park, 

 consideration of the world picture introduces problems. Are the 

 European bears really the "same species" as the Yellowstone bears? 

 Are the polar bears really a "different species"? Are these questions 

 biologically important? 



This problem is also common in plants. As with animals, it is par- 

 ticularly evident in those forms that have a circumpolar or circum- 



Fig. 1 1.3 I Closely related butterflies of the genus Nymphalis. Upper 

 left, N. milberti, Wyoming; upper right, N. caschmirensis, Nepal; lower 

 left, N. urticae, Sakhalin; lower right, N. iirticae, Hungary. 



