108 THE WOELD OF LIFE 



ever reaching absolute uniformity) as seems best adapted to 

 bring about the greatest productivity, together with extreme 

 diversity in every department of the great world of life. 



The large amount of diversity of species we have seen to oc- 

 cur in single fields long subject to almost identical conditions 

 in our own country, wdth the additional fact that no plot of a 

 fev7 square yards has exactly the same grouping of species and 

 individuals as any of the other plots, yet each plot produces 

 very nearly the same number of species, will enable us in some 

 degree to appreciate the conditions of the tropics. There we 

 see enormous areas subject to almost identical conditions of 

 soil, climate, and rainfall, yet in every part of it exhibiting, 

 amid a general -uniformity of type, a wonderful diversity in 

 the shapes and structures of the forms of life, and a no less 

 w^onderful balance and adaptation of each to all. How this 

 result has been actually brought about in the course of evolu- 

 tion through the ages we shall better understand after a brief 

 exposition of the factors wdiich have been the immediate causes 

 of the two great phenomena, continuous evolution, with con- 

 tinuous adaptation. 



