It seems, therefore, to me extremely probable that they will
have taken the places of, and thus exterminated, not only their parents (A)
and (I), but likewise some of the original species which were most nearly
related to their parents. Hence very few of the original species will have
transmitted offspring to the fourteen-thousandth generation. We may suppose
that only one (F), of the two species which were least closely related to
the other nine original species, has transmitted descendants to this late
stage of descent. {123}

The new species in our diagram descended from the original eleven species,
will now be fifteen in number. Owing to the divergent tendency of natural
selection, the extreme amount of difference in character between species
a^{14} and z^{14} will be much greater than that between the most different
of the original eleven species. The new species, moreover, will be allied
to each other in a widely different manner. Of the eight descendants from
(A) the three 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} and m^{14},
will be nearly related one to the other, but from having 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 even a
distinct genus.

The six descendants from (I) will form two sub-genera or even genera. But
as the original species (I) differed largely from (A), standing nearly at
the extreme points of the original genus, the six descendants from (I)
will, owing to inheritance alone, differ considerably from the eight
descendants from (A); the two groups, moreover, are supposed to have gone
on diverging in different directions. The intermediate species, also (and
this is a very important consideration), which connected the original
species (A) and (I), have all become, excepting (F), extinct, and have left
no descendants. Hence the six new species descended from (I), and the eight
descended from (A), will have to be ranked as very distinct 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 {124} more parent-species are supposed