EVOLUTION AS A NATURAL PUOCICSS UU 



As a consequence of the many-sided stniKgle for 

 existence, the interrelations of a series of species will 

 approach a condition of orpiilihriiim in an area where 

 the natural circumstances remain relatively undislurlM-.j 

 for a long time. For examj)le, anions the field-mice of 

 one generation, just as many individuals will survive as 

 will be able to find food and to escape hereditary foea 

 such as cats and snakes and owls. The numhrr of owls, 

 in their turn, wdll be determined by the number of 

 available mice and other food organisms, as well us 

 by the severity of the adverse circumstances that caui^ 

 elimination of the less fit among the fledglings brouglit 

 into the world. The vital chain of connections Ls 

 sometimes astonishingly long and intricate. One n»- 

 markable illustration is given by Fiske, a-s an elal)ora- 

 tion of an example cited by Darwin. He points out 

 that the fine quahty of the traditional roast beef of Kng- 

 land is directly determined by the number of elderly 

 spinsters in that country. The chain of circumstances 

 is as follows : the quahty of the clover fields, furnish- 

 ing the best food for cattle, dei)ends largely upon the 

 visits to the clover-blossoms b}' wild bees, that accom- 

 plish the fertilization of the flowers by carrying i)ollen 

 upon their bodies from one plant to another. Field- 

 mice devour the young in the nests of these l)ees. .<o if 

 there are few field-mice there will ])v many bees, and 

 consequently better grazing for the cattle. The number 

 of field-mice will vary according to the abundance 

 of cats, and so the number of these domestic animals will 

 exert an influence upon the whole foregoing rhain of 

 forms. But, as Fiske points out, cats are the favorite 

 companions of elderly spinsters; therefore, if there are 



