NATURAL SELECTION 173 



some degree distinct from the three first-named species; 

 and lastly, o'*, e*\ and m'* will be nearly related one 

 to the other, but, from having diverged at the first com- 

 mencement of the process of modification, will be widely 

 different from the other five species, and may constitute 

 a sub-genus or a distinct genus. 



The six descendants from (I) will form two sub-genera 

 or genera. But as the original species (I) differed largely 

 from (A), standing nearly at the extreme end of the orig- 

 inal genus, the six descendants from (I) will, owing to 

 inheritance alone, differ considerably from the eight de- 

 scendants from (A); the two groups, moreover, are sup- 

 posed to have gone on diverging in different directions. 

 The intermediate species, also (and this is a very impor- 

 tant consideration), which connected the original species 

 (A) and (I), have all become, excepting (F), extinct, and 

 have left no descendants. Hence the six new species de- 

 scended from (I), and the eight descendants from (A), 

 will have to be ranked as very distinct genera, or even 

 as distinct sub-families. 



Thus it is, as I believe, that two or more genera are 

 produced by descent witb modification from two or more 

 species of the same genus. And the two or more parent- 

 species are supposed to be descended from some one spe- 

 cies of an earlier genus. In our diagram, this is indi- 

 cated by the broken lines, beneath the capital letters, 

 converging in sub-branches downward toward a single 

 point; this point represents a species, the supposed pro- 

 genitor of our several new sub-genera and genera. 



It is worth while to reflect for a moment on the char- 

 acter of the new species f", which is supposed not to 

 have diverged much in character, but to have retained 



. 



