POLAR BEAR CACTI 



Analogies between Polar Bears and Shaggy-Haired Cacti of the High Andes of 



Peru As Examples of Adaptation to Special Conditions 



of Existence 



(). F. Cook 



Bniraii of Plant Industry, Washington, D. C, 



and Alice Carter Cook 



THE polar bear represents one of the 

 traditional examples of adaptation 

 to special conditions of existence. 

 It is easy tounderstandthatadark 

 colored bear or a short haired bear would 

 be at a great disadvantage among the 

 arctic snow fields. The polar bear differs 

 from all his kindred in these two features 

 that are necessary to make him a 

 success in his own peculiar environment . 

 It seems clear in such cases that there 

 is a real relation between the special 

 characters and the special environment, 

 and many writers have believed that 

 the relation was one of cause and effect, 

 that in some way or other the environ- 

 ment itself had produced the appropri- 

 ate characters. Many, indeed, have 

 gone further and urged that all charac- 

 ters must have environmental import- 

 ance, and hence that the environment 

 must be the underlying cause of the 

 evolutionary progress of species. 

 Nevertheless, nobody has explained 

 how the external conditions are able to 

 bring about evolutionary changes in 

 species. Environmental causes of evo- 

 lution have not been found, in spite 

 of a century of search by Lamarck and 

 Darwin, and their numerous followers. 

 The ' relation between evolution and 

 environment is still to be considered 

 as an open question, in view of the 

 widely divergent opinions that continue 

 to be expressed by writers on the subject. 

 Adaptation may be defined as the 

 possession of characters of environ- 

 mental fitness. In a sufficiently general 

 sense all characters may be considered 

 as adaptive, for if any were definitely 

 nonadaptive they would interfere with 

 the existence of the species. Neverthe- 

 less, some characters are much more 



ob\-ioush' adapti\"e than others, as in 

 this case of the polar bear, the only 

 member of its group that is able to 

 live in its special environment by virtue 

 of peculiar characters, the lack of which 

 appears to exclude other species. 



A CACTUS OF THE ANDES 



In the Southern Hemisphere is an- 

 other example of adaptation which 

 may be compared to this of the polar 

 bear. Many exposed slopes on the 

 bleak plateaus of the high Andes are 

 dotted with clumps of pure white 

 cacti that look from a distance like 

 small masses of snow. On closer view, 

 the shaggy white hair of these cacti 

 makes them appear like small sheep 

 or poodle-dogs, or like reduced carica- 

 tures of the denizens of the arctic 

 regions. We are so accustomed to 

 think of cacti primarily as desert 

 plants, peculiarly adapted to hot, dr\' 

 deserts, that they seein distinctly out 

 of place on the cold plateaus of the high 

 Andes of southern Peru. 



vSome long-haired or canescent cacti are 

 found in lowland deserts. Hair several 

 inches long covers the young plants 

 and the growing parts of older ones so 

 suggestively that they are popularh- 

 known as "old men" or "old women." 

 These hairy desert forms, however, do 

 not seem to enjoy any important 

 advantage over their unprotected, naked 

 relatives that are just as common in 

 these same localities. But in the high 

 Andes there is a species so entire!}' 

 covered with long white hairs that it 

 may appropriately be called the Polar 

 Bear Cactus. In some localities it is 

 very abundant, dotting the grassy 

 slopes like flocks of diminutive shee]) 



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