CiiAr. IV. NATUEAL SELECTION. 119 



bo noavly related from liaving^ recently branched off from a'°/ 

 J/*, and /'*, from liavin": diverged at an earlier period from a'', 

 \\\\\ be in some deo^ree distinct from the three first-named spe- 

 ties ; and lastly, o'\ e'*, and »i'*, will be nearly related one to 

 the other, but, from havinfj; diverf^ed at the first commence- 

 ment of tlie 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 original genus, 

 llie six descendants from (I) will, owing to inheritance alone, 

 differ considerably from the eight descendants from (A) ; the 

 two groups, moreover, are supposed to have gone on diverging 

 in different directions. The intermediate species, also (and 

 this is a very important consideration), which connected the 

 original species (A) and (I), have all become, excepting (F), 

 extinct, and have left no descendants. Hence the six new spe- 

 cies descended from (I), and the eight descended from (A), 

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

 tinct sub- families. 



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

 duced, by descent Avith modification, from two or more species 

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

 supposed to have descended from some one species of an ear- 

 lier genus. In our diagram, this is indicated by the broken 

 lines, beneath the capital letters, converging in sub-branches 

 downward toward a single point; this point representing a 

 single species, the supposed progenitor of our several new sub- 

 genera and genera. 



It is worth while to reflect for a moment on the character 

 of the new species f'*, which is supposed not to have diverged 

 much in character, but to have retained the fomi of (F), either 

 unaltered or altered only in a slight degree. In this case, its 

 allinitics to the other fourteen new species Avill be of a curious 

 and circuitous nature. Having descended from a form which 

 stood l)etwe(Mi the two parent-species (A) and (I), now sup- 

 posed to 1)0 extinct and imknown, it will be in some degree in- 

 l«-rmediate in character between the two groups descended 

 from these species. I5ut as these two groups have gone on 

 diverging in character from the type of their parents, the new 

 species (f'*) will not be directly intermediate between them, 

 but ratlier l^etween t}^es of the two groups; and every 



