animal life presents to view the beginning of a protracted history; the highest order of animate existence indicates the stage of advance at which we observe things at the present period. For such a theory the history of individual development belonging to whatever order, and the history of distinct orders as indicating improvement and deviation of whatever aspect, present evidence of special value. The most important causes. relied upon as contributing to the formation of a scientific theory may be presented under these four heads-(1) The action of external causes as provided for by environment; (2) power of adaptability within each organism, providing for changes according to requirement from without, which may be described as "adaptive changes of structure;" (3) "the struggle for existence," in accordance with which the strongest gain the mastery and consequent advantage in obtaining the means of subsistence; and (4) "natural selection" among the sexes, giving to the offspring all advantages according to the laws of hereditary descent.

The essential feature in this theory is the power of adaptability inherent in the organism.

This is postulated as characteristic of all organized existence; and it is implied, that this power of adaptability multiplies in a degree approximating to the measure of complexity belonging to the organism. The inherent capacity for deviation is thus much less in the mollusk than in the bird; and in the bird much less than in the quadruped. Thus the development process which must, according to this view, have been exceedingly slow in the earlier stages, must have been greatly accelerated when more complex organisms had come into existence, and all the advantages accrued from greater diver sity of materials. Such is a brief outline of the theory; and looked at simply as a theory, there is a manifest attraction in the boldness of the conception, and the wide sweep of the generalization which it includes. Taken merely as an intellectual representation setting forth a conceivable order of things in the universe, it has a great deal to command attention and awaken interest. It is, indeed, a novelty in the history of scientific thought, and as such at variance with previous conceptions, both scientific and non-scientific. But it is no more at variance with religious

thought, than with ordinary notions of preceding times; while to the author whose name is now associated with it all over the scientific world, it is a more striking testimony of the marvels of creative power,* than notions previously current, which regarded it as historically true that every existing variety of animal was launched into being by a distinct creative act. Whatever may be the ultimate view of the history of life on the earth, based on purely scientific data,—and we are still a far way removed from what may be regarded as scientific evidence for such a view,—the fewer the primordial forms to which the multiplicity of existing species can be traced, the greater is the marvel which science presents, and the more convincing becomes the intellectual necessity by which we travel back to a Supernatural Intelligence as the source of all. On the other hand, the slow process by which scientific research tends to make out the natural history of living organisms far removed from each other in the scale of being, tracing many groups to a common parentage, and assigning their appearance in the world to

* Origin of Species, p. 577.

distinct periods in its history, will be seen to be so far anticipated and favored by the graphic description of the introduction of animal life given in the opening page of revelation, where different orders are assigned to successive epochs.

While, however, these things are said at the outset, as affording commencement for the study of an evolution theory, and delivering us from the supposition that there is an inevitable antagonism between science and recognition of the supernatural, we revert to the ruling principle for this whole inquiry, that science must prosecute its own researches, unfettered by forecast of consequences; and that the Bible is not to be handled as if it were a book of science, for it neither lays restraints upon human inquiry, nor delivers us from the need for it.

The best method for entering upon a study of the theory of evolution by natural selection is to take Mr. Darwin's own account of the manner in which it began to take shape before his mind. In his "historical sketch of the recent progress of opinion on the origin of species," he traces to Lamark the first sug*The Origin of Species, xiii. 4th ed.

gestions on the subject, directing public attention to the question in 1801; thereafter a succession of naturalists including St. Hilaire, Wells, and Patrick Matthew, from separate and incidental observations, dwelt upon the difficulty of distinguishing species, and on the evidence of an archetypal idea, or common plan of structure, being applicable in the history of whole orders. Mr. Darwin then gives the following biographical references at the outset,-"When on board H. M. S. 'Beagle,' as naturalist, I was much struck with certain facts in the distribution of the organic beings inhabiting South America, and in the geological relations of the present to the past inhabitants of that continent. These facts seemed to throw some light on the origin of species -that mystery of mysteries, as it has been called by one of our greatest philosophers. On my return home, it occurred to me in 1837, that something might perhaps be made out on this question by patiently accumulating and reflecting on all sorts of facts which could possibly have any bearing on it. After five years' work I allowed myself to speculate on the subject, and drew up some short notes; these I enlarged in 1844 into a sketch