ON THE NATURE OF THE AFFINITIES CONNECTING ORGANIC BEINGS.
As the modified descendants of dominant species, belonging to the larger
genera, tend to inherit the advantages which made the groups to which they
belong large and their parents dominant, they are almost sure to spread
widely, and to seize on more and more places in the economy of nature. The
larger and more dominant groups within each class thus tend to go on
increasing in size, and they consequently supplant many smaller and feebler
groups. Thus, we can account for the fact that all organisms, recent and
extinct, are included under a few great orders and under still fewer
classes. As showing how few the higher groups are in number, and how
widely they are spread throughout the world, the fact is striking that the
discovery of Australia has not added an insect belonging to a new class,
and that in the vegetable kingdom, as I learn from Dr. Hooker, it has added
only two or three families of small size.
In the chapter on geological succession I attempted to show, on the
principle of each group having generally diverged much in character during
the long-continued process of modification, how it is that the more ancient
forms of life often present characters in some degree intermediate between
existing groups. As some few of the old and intermediate forms having
transmitted to the present day descendants but little modified, these
constitute our so-called osculant or aberrant groups.
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