OF NATURAL SELECTION. 107 



original eleven species. The new species, moreover, will be 

 allied to each other in a widely different manner. Of the 

 eight descendants from (A) the three marked a 14 , q u , p u , will 

 be nearly related from having recently branched off from a 19 ; 

 b li and / 14 , from having diverged at an earlier period from 

 a 5 , will be in some degree distinct from the three first-named 

 species ; and lastly, o 14 , e 14 , and m u will be nearly related 

 one to the other, but, from being 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 original genus, 

 the 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 diver- 

 ging 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, except (F), 

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

 species descended 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 pro- 

 duced by descent, with 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 species of an earlier 

 genus. In our diagram this is indicated by the broken lines 

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

 ward toward a single point : this point represents a 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 14 , which is supposed not to have diverged 

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

 either unaltered or altered only in a slight degree. In this 

 case its affinities to the other fourteen new species will be of 

 a curious and circuitous nature. Being descended from a 

 form that stood between the parent-species (A) and (I), now 

 supposed to be extinct and unknown, it will be in some degree 

 intermediate in character between the two groups descended 

 from these two species. But as these two groups have gone 

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



