158 EVOLUTION 



intercrossing, and the resultant finely adjusted 

 adaptation of flower and insect to each other 

 through the preservation of their respective 

 advantageous variations. 



Circumstances favourable for the production 

 of new forms through natural selection are 

 great variability, large numbers of individuals, 

 the complex effects of intercrossing, isolation 

 in confined areas (yet probably still more an 

 extension over continental areas, especially if 

 oscillating 4n level), and considerable lapse of 

 time. But the lapse of time by itself must 

 not be supposed to do anything (as if the 

 forms of life were undergoing change by some 

 innate law), but merely to afford increased 

 opportunity for variation and environmental 

 change. Extinction, to which rare species 

 are on the way, is the last word of natural 

 selection. 



The divergence of character brought about 

 by artificial selection in domestic breeds is 

 efficiently paralleled in Nature, since the 

 more diversified the offspring of each species, 

 the more they will seize on diverse places in 

 the economy of Nature, and so increase in 

 numbers. The greatest amount of life can 

 be supported by increased diversification of 

 structure, each species being adapted to a 

 particular set of conditions. This divergence 



