6 



Species and 

 Species Change 



Although natural selection directs change in indi- 

 vidual local populations, it is the establishment of 

 change in species as a whole which has led to the 

 great variety of living types that constitute the vast 

 family tree of nature. Each line of this family tree is 

 one species thick. During the passage of species 

 through time, two evolutionary processes occur 

 (Fig. 45): (1) species change and become new and 

 often radically different kinds of organisms, and ( 2 ) 

 species give rise to daughter species and in this way 

 increase the number of phylogenetic lines. In this 

 chapter we will discuss the change in species pro- 

 gressing through time. 



RECOGNITION OF SPECIES 



The species are the different kinds of plants and ani- 

 mals. Typically each kind breeds true generation 



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