Here his appearance will attract
birds of the other sex; and then by the law of heredity, his offspring
are sure to repeat the coloured feathers, till at last a regularly
bright-crested species-arises. In this way _natural variability_, acted
on by the necessities of _environment_ (which cause the _survival of the
fittest_ specimens) and the principle of _heredity_, viz., that the
offspring repeat the features of the parents, aided by the principle of
_sexual selection_, have been the origin and cause of all the species we
see in the world.
Thus we have an unbroken series--certain substances condensing out of
cosmic vapour, some of them combining to form the variety of rocks,
soils, metals, &c., and others giving rise to protoplasm which grows'
and develops into a thousand shapes and hues, of insect, fish, reptile,
bird, and beast.
And then it is, that charmed with the completeness and symmetry of such
a theory, and overlooking the difficulties that crop up here and
here--demanding some Power from without to bridge them over--certain
extreme theorists have rushed to the conclusion that in all this there
is no need of any external Creator or Providence--nothing but what we
call secondary causes, ordinary causes which we see at work around us
all day and every day.
How inconceivable, they add, is the truth of the Book of Genesis, which
asserts the successive creation of fully-formed animals by sudden acts
of command; and all accomplished in a few days at the beginning of the
world's human history!
This I believe to be a fair outline, though of course a very rough and
general one, of the Theory of Evolution as regards the forms of matter
and living organisms.
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