This
grand fact of the grouping of all organic beings under what is called the
Natural System, is utterly inexplicable on the theory of creation.
As natural selection acts solely by accumulating slight, successive,
favourable variations, it can produce no great or sudden modifications; it
can act only by short and slow steps. Hence, the canon of "Natura non
facit saltum," which every fresh addition to our knowledge tends to
confirm, is on this theory intelligible. We can see why throughout nature
the same general end is gained by an almost infinite diversity of means,
for every peculiarity when once acquired is long inherited, and structures
already modified in many different ways have to be adapted for the same
general purpose. We can, in short, see why nature is prodigal in variety,
though niggard in innovation. But why this should be a law of nature if
each species has been independently created no man can explain.
Many other facts are, as it seems to me, explicable on this theory. How
strange it is that a bird, under the form of a woodpecker, should prey on
insects on the ground; that upland geese, which rarely or never swim, would
possess webbed feet; that a thrush-like bird should dive and feed on
sub-aquatic insects; and that a petrel should have the habits and structure
fitting it for the life of an auk! and so in endless other cases. But on
the view of each species constantly trying to increase in number, with
natural selection always ready to adapt the slowly varying descendants of
each to any unoccupied or ill-occupied place in nature, these facts cease
to be strange, or might even have been anticipated.
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