Chap. XV.] BECAPITULATION. 287 



and kinds of resemblance to their parents, — in being 

 absorbed into each other by successive crosses, and in 

 other such points, — as do the crossed offspring of ac- 

 knowledged varieties. This similarity would be a strange 

 fact, if species had been independently created and 

 varieties had been produced through secondary laws. 

 f If we admit that the geological record is imperfect 

 to an extreme degree, then the facts, which the record 

 does give, strongly support the theory of descent with 

 modification^ New species have come on the stage slowly 

 and at successive intervals ; and the amount of change, 

 after equal intervals of time, is widely different in dif- 

 ferent groups, friie extinction of species and of whole 

 groups of species, which has played so conspicuous a 

 part in the history of the organic world, almost inevitably 

 follows from the principle of natural selection ; for old 

 forms are supplanted by new and improved forms!] 

 Neither single species nor groups of species reappear 

 when the chain of ordinary generation is once broken. 

 The pradual diffusion of dominant forms, with the slow 

 modification of their descendants, causes the forms of 

 life, after long intervals of time, to appear as if they had 

 changed simultaneously throughout the world. The fact 

 of the fossil remains of each formation being in some 

 degree intermediate in character between the fossils in 

 the formations above and below, is simply explained by 

 their intermediate position in the chain of descent. The 

 grand fact that all extinct beings can be classed with 

 all recent beings, naturally follows from the living and 

 the extinct being the offspring of common parents. As 

 species have generally diverged in character during their 

 long course of descent and modification, we can under- 

 stand why it is that the more ancient forms, or early 



