But we must proceed a step further; for those who would believe in the sufficiency of unaided Evolution, bid us bear in mind how very elementary the dawn of instinct or the beginning of reason is in the lowest forms which are classed as animal, and how very small is the gap[1] between some highly organized plants and some animal forms, and argue therefore that they may justly regard the distinction as of minor importance, and hope that the “missing link” will be yet discovered and proved.  At any rate, they minimize the difference, and urge that it is of no account if at least they can establish the sufficiency of a proved development extending unbroken from the lowest to the highest animal form.  And having fixed attention on this side, no doubt there is a long stretch of smooth water over which the passage is unchecked.

[Footnote 1:  At the risk of repetition I will remind the reader that nature contains nothing like a progressive scale from plant to animal.  It is never that the highest plant can be connected with the lowest animal as in one series of links.  The animal kingdom and the plant kingdom are absolutely apart.  Both start from similar elementary proteinaceous structures; and both preserve their development upwards—­each exhibiting some of the features of the other.  It is at the bottom of each scale that resemblance is to be found, not between the top of one and the lowest members of the other.]

The Evolution theory is that all the different species of animals, birds, and other forms of life have been caused by the accumulation and perpetuation of numerous small changes which began in one or at most a few elementary forms, and went on till all the thousands of species we now know of were developed.[1] It is a fact that all organic forms have a certain tendency to vary.  I need only allude to the many varieties of pigeons, horses, cattle, and dogs which are produced by varying the food, the circumstances of life and so forth, and by selective breeding.

The contention then is:  given certain original simple forms of life, probably marine or aquatic—­for it is in the water that the most likely occur—­these will gradually change and vary, some in one direction, some in another; that the changes go on increasing, each creature giving birth to offspring which exhibits the stored-up results of change, till the varied and finished forms—­some reptile, some bird, some animal—­which we now see around us, have been produced.  And at last man himself was developed in the same way.  All this, observe, is by the action of just such ordinary and natural causes as we now see operating around us—­changes in food and in climate, changes in one part requiring a corresponding change in others, and so on.

[Footnote 1:  The reader may find this admirably put in Wallace, “Contributions to the Theory of Natural Selection,” p. 302.]