aces 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 (E and F) which were least closely related to the
other nine original species, has transmitted descendants to this late
stage of descent.

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 a14 and z14 will be much greater than that between the
most distinct 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 a14, q14, p14, will be nearly
related from having recently branched off from a10; b14 and f14, from
having diverged at an earlier period from a5, will be in some degree
distinct from the three first-named species; and lastly, o14, e14, and
m14, 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
a distinct genus.

The six descendants from (I) will form two sub-genera or genera. But as
the original species (I) differed largely from (A), standing nearly
at the extreme end 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, except (F), extinct, and
have left no descendants. Hence the six new species descended from
(I), and the eight descendants 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 more parent-species are supposed to be descended from
some one species of an earlier genus. In our diagram this is indicated
by the broken lines beneath the c