At first, the materialist holds, protoplasm appeared in very simple forms, just such as can still be found within the sea, and in ponds.  But the lower organized forms of life are extremely unstable, and a different environment will always tend to evoke continuous small changes, so that there may be advance in forms of all kinds.  For if by chance[1] some creature exhibits a variation which is favourable to it in the circumstances in which it is placed, that creature will be fitter than the others which have not that variation.  And so the former will survive, and as they multiply, their descendants will inherit the peculiarity.  Thus, in the course of countless generations, change will succeed change, till creatures of quite a complex structure and specialized form have arisen.  As the circumstances of life are always infinitely various, the developments take place in many different directions; some fit the creature for life in deep seas, some for flying in the air, some for living in holes and crevices, some for catching prey by swift pursuit, others for catching it by artful contrivance, and so forth.  Many changes will also arise from protective necessity:  if an insect happens to be like a dead leaf, it will escape the notice of birds which would snap up a conspicuously coloured one; and so the dull-coloured will survive and perpetuate his kind, while the others are destroyed.  On the other hand, beauty in colour and form may have its use.  This is chiefly exhibited in the preference which the females of a species show for the adorned and showy males.

[Footnote 1:  Not really of course “by chance,” but simply owing to such circumstances as cannot be accounted for by any direct antecedents.]

Supposing an organism developed so far as to be a bird, but only with dull or ugly feathers.  By accident one male bird, say, gets a few bright-coloured feathers on his head.  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.