476 RECAPITULATION. Chap. XIV. 



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 organic beings 

 belong to the same system with recent beings, falling 

 either into the same or into intermediate groups, follows 

 from the living and the extinct being the offspring 

 of common parents. As the groups which have de- 

 scended from an ancient progenitor have generally 

 diverged in character, the progenitor with its early de- 

 scendants will often be intermediate in character in 

 comparison with its later descendants ; and thus we can 

 see why the more ancient a fossil is, the oftener it stands 

 in some degree intermediate between existing and allied 

 groups. Kecent forms are generally looked at as* being, 

 in some vague sense, higher than ancient and extinct 

 forms ; and they are in so far higher as the later and 

 more improved forms have conquered the older and less 

 improved organic beings in the struggle for life. Lastly, 

 the law of the long endurance of allied forms on the 

 same continent, — of marsupials in Australia, of edentata 

 in America, and other such cases, — is intelligible, for 

 within a confined country, the recent and the extinct 

 will naturally be allied by descent. 



Looking to geographical distribution, if we admit that 

 there has been during the long course of ages much 

 migration from one part of the world to another, owing 

 to former climatal and geographical changes and to 

 the many occasional and unknown means of dispersal, 

 then we can understand, on the theory of descent with 

 modification, most of the great leading facts in Distribu- 

 tion. We can see why there should be so striking a 

 parallelism in the distribution of organic beings through- 

 out space, and in their geological succession throughout 

 time ; for in both cases the beings have been connected 

 by the bond of ordinary generation, and the means of 



