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p 14 , 1859 1861 1866 1869 1872
p 14 1860

f 14 , 1859 1861 1866 1869 1872
f 14 1860

m 14 , 1859 1861 1866 1869 1872
m 14 1860

and as these latter two genera, both from continued divergence of character and from inheritance from a different parent, will differ 1859 1860 1861 1866
differing 1869 1872

three genera descended from (A), the two little 1859 1860 1861 1866
descendants of (A). These two 1869 1872

one species of a 1859 1860 1861 1866
some 1869 1872

the extinct species lived at
various remote
very ancient
epochs when the branching lines of descent had diverged less.
I see no reason to limit the process of modification, as now explained, to the formation of genera alone. If, in
the
our
diagram, we suppose the amount of change represented by each successive group of diverging dotted lines to be
very
very
great, the forms marked a 14 to p 14 ,
, those
those
marked b 14 and f 14 ,
, and
and
those marked o 14 to m 14 ,
, will
will
form three very distinct genera. We shall also have two very distinct genera descended from
(I),
(I);
and as these latter two genera, both from continued divergence of character and from inheritance from a different parent, will differ widely from the three genera descended from (A), the two little groups of genera will
thus form
form
two distinct families, or
even
even
orders, according to the amount of divergent modification supposed to be represented in the diagram. And the two new families, or orders,
are
will have
descended from two species of the original
genus,
genus;
and these
two species
two species
are supposed to
be
have
descended from one species of a still more ancient and unknown
form.
genus.
We have seen that in each country it is the species
belonging to
of
the larger genera which oftenest present varieties or incipient species. This, indeed, might have been expected;
for,
for
as natural selection acts through one form having some advantage over other forms in the struggle for existence, it will chiefly act on those which already have some advantage; and the largeness of any group shows that its species have inherited from a common ancestor some advantage in common. Hence, the struggle for the production of new and modified
descendants
descendants,
will mainly lie between the larger
groups
groups,
which are all trying to increase in number. One large group will slowly conquer another large group, reduce its numbers, and thus lessen its chance of further variation and improvement. Within the same large