NATURAL SELECTION 97 



marked a 14 , q 14 , p 14 , will be nearly related from having recently 

 branched off from a 10 ; b 14 and f 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 y and m 14 will be 

 nearly related one to the other, but, from being diverged at the 

 first commencement 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 con- 

 siderably from the eight descendants from (A) ; the two groups, 

 moreover, are supposed to have gone on diverging in different di- 

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

 tant consideration), which connected the original species (A) and 

 (I), have all become, except (F), extinct, and have left no de- 

 scendants. Hence the six new species descended from (I), and the 

 eight descendants from (A), will have to be ranked as very dis- 

 tinct genera, or even as distinct sub-families. 



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

 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 downward 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 na- 

 ture. 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 new species (f 14 ) will not be directly intermediate between 

 them, but rather between types of the two groups; and every natu- 

 ralist will be able to call such cases before his mind. 



In the diagram each horizontal line has hitherto been supposed 

 to represent a thousand generations, but each may represent a 



