476 
RECAPITULATION. 
Chap. XTV. 
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. Eecent 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 
