Birds are
attracted to the nutritious matter enclosing the seeds, and, as
it is an advantage to the plant that its seeds be scattered
beyond the already populated area, by passing through the
alimentary canal of the bird, and being discharged with its
excrements, a fresh line of evolution leads to the appearance of
the large and coloured fruits. The birds, again, turn upon the
swarming insects, and the steady selection they exercise leads to
the zigzag flight and the protective colour of the butterfly, the
concealment of the grub and the pupa, the marking of the
caterpillar, and so on. We can understand the living nature of
to-day as the outcome of that teeming, striving, changing world
of the Tertiary Era, just as it in turn was the natural outcome
of the ages that had gone before.
CHAPTER XVII. THE ORIGIN OF OUR MAMMALS
In our study of the evolution of the plant, the insect, and the
bird we were seriously thwarted by the circumstance that their
frames, somewhat frail in themselves, were rarely likely to be
entombed in good conditions for preservation. Earlier critics of
evolution used, when they were imperfectly acquainted with the
conditions of fossilisation, to insinuate that this fragmentary
nature of the geological record was a very convenient refuge for
the evolutionist who was pressed for positive evidence.
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