the upper pliocene, the pleistocene and strictly modern beds, of
Europe, North and South America, and Australia, from containing fossil
remains in some degree allied, and from not including those forms which
are only found in the older underlying deposits, would be correctly
ranked as simultaneous in a geological sense.
The fact of the forms of life changing simultaneously, in the above
large sense, at distant parts of the world, has greatly struck those
admirable observers, MM.
de Verneuil and d Archiac. After referring to the parallelism of the
pal ozoic forms of life in various parts of Europe, they add, If
struck by this strange sequence, we turn our attention to North
America, and there discover a series of analogous phenomena, it will
appear certain that all these modifications of species, their
extinction, and the introduction of new ones, cannot be owing to mere
changes in marine currents or other causes more or less local and
temporary, but depend on general laws which govern the whole animal
kingdom. M. Barrande has made forcible remarks to precisely the same
effect. It is, indeed, quite futile to look to changes of currents,
climate, or other physical conditions, as the cause of these great
mutations in the forms of life throughout the world, under the most
different climates. We must, as Barrande has remarked, look to some
special law. We shall see this more clearly when we treat of the
present distribution of organic beings, and find how slight is the
relation between the physical conditions of various countries, and the
nature of their inhabitants.
This great fact of the parallel succession of the forms of life
throughout the world, is explicable on the theory of natural selection.
New species are formed by new varieties arising, which have some
advantage over older forms; and those forms, which are already
dominant, or have some advantage over the other forms in their own
country, would naturally oftenest give rise to new varieties or
incipient species; for these latter must be victorious in a still
higher degree in order to be preserved and to survive. We have distinct
evidence on this head, in the plants which are dominant, that is, which
are commonest in their own homes, and are most widely diffused, having
produced the greatest number of new varieties. It is also natural that
the dominant,
varying, and far-spreading species, which already have invaded to a
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