174 THE ORIGIN OF SPECIES 



the form of (F), either unaltered or altered only in a 

 slight degree. In this case, its afliaities to the other 

 fourteen new species will be of a curious and circui- 

 tous nature. Being descended from a form which stood 

 between the parent-species (A) and (I), now supposed to 

 be extinct and unknown, it will be in some degree inter- 

 mediate 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'*) will not be directly inter- 

 mediate between them, but rather between types of the 

 two groups; and every naturalist 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 million or more generations; it may also 

 represent a section of the successive strata of the earth's 

 crust including extinct remains. We shall, when we 

 come to our chapter on Geology, have to refer again 

 to this subject, and I think we shall then see that the 

 diagram throws light on the affinities of extinct beings, 

 which, though generally belonging to the same orders, 

 families, or genera, with those now living, yet are often, 

 in some degree, intermediate in character between existing 

 groups; and we can understand this fact, for the extinct 

 species lived at various remote epochs when the branch- 

 ing lines of descent had diverged less. 



I see no reason to limit the process of modification, 

 as now explained, to the formation of genera alone. If 

 in the diagram we suppose the amount of change repre- 

 sented by each successive group of diverging dotted lines 

 to be great, the forms marked a'* to p'\ those marked 



