DESCENT WITH CHANGE 



36$ 



Fig. 236. — Geographical distribution of Song Sparrows. Each different 

 number indicates habitat of a subspecies. "We find complete integradation in 

 color and in size. Nowhere can one draw the line. As the climatic conditions 

 under which the birds live change, the birds keep pace. Here we have a species 

 in flower, as it were, a single Song Sparrow stalk with its twenty-nine blos- 

 soms, any one of which might make an independent growth as a species if it 

 were separated from the parent stem. Doubtless some day the separation will 

 come, when we shall have several sDecies, each with its groups of races, but 

 at present we have only one species, divided into some twenty-nine sub- 

 species, or species in process of formation." (Chapman.) 



