of proportion between two or more of the feathers, is recorded in eleven species of birds. Color and marking vary to an equal extent; the dark streaks on the under surface of Melozpiza melodia (the American song sparrow) being sometimes reduced to narrow lines, while in other specimens they are so enlarged as to cover the greater part of the breast and sides of the body, sometimes uniting on the middle of the breast to a nearly continuous patch. In one of the small spotted woodthrushes, Turdus fuscescens, the colors are sometimes very pale, and the markings on the breast reduced to indistinct narrow lines; while in other specimens the general color is much darker, and the breast-markings dark, broad, and triangular. All the variations here mentioned occur between adult males, so that there is no question of differences of age or sex, and the pair last referred to were taken at the same place and on the same day."1

Secondly, geologists are slow to grant the validity of mathematical calculations regarding the age of the earth. Both divisor and dividend are so indeterminate that the quotient must be still more conjectural. The amount of uncertainty is illustrated in the extreme limits which Sir W. Thomson sets for the date of the first consolidation of the earth's crust. It can hardly have 1 Wallace's Island Life, pp. 55, 56.

occurred less than twenty, nor more than four hundred, million years ago." 1

V. Existing Difficulties of Classification Inevitable under any Hypothesis.3

This is not a direct objection to Darwinism, but is aimed at one of the prominent pillars of proof on which the theory rests. In this objection it is assumed only, first, that there "are different laws," under which" all existing substances or beings of which we have any scientific knowledge exist"; secondly, that there is a limited number of elements from which combinations can be made. With these self-imposed restrictions which the Creator has put upon his work in the material world, the problem of classification is one of permutations and combinations. "The limits to the possible number of combinations become more and more restricted, as we burden these combinations with laws more and more complicated." 3 For example, if it be required to find the number of words of five letters each which can be formed out of the English alphabet, and if there be no other restriction on the combinations than that there be five letters in each, we shall have the number 7,890,000.

1 Origin of Species, p. 286. See also Lyell, Principles of Geology, Vol. i. pp. 234, 235; also, Dana, Manual of Geology (1st ed.), p. 684.

2 See North British Review, Vol. xlvi. pp. 305-313.

Ibid., p. 307.

If, however, we insert the condition that no two of the combinations shall begin with the same letter, the number of possible words of five letters is reduced to twenty-six. If it be further stipulated that no two of the words shall have any letter in common, the number is reduced to five.

1

Now, animals and plants are combinations of inorganic elements under conditions of almost inconceivable complexity. These elements are to be so arranged as to constitute an "eating, breathing, moving, feeling, self-reproducing thing." How else than in a continuous series of combinations, each resembling its neighbor, could these elements be arranged under these conditions, if there were to be an indefinite number of individuals? Professor Agassiz 2 seems to affirm that the possibilities of economical construction are exhausted in the four grand divisions of the animal kingdom-the Radiate, the Moluscan, the Articulate, and the Vertebrate. Mathematical laws determine that varieties, if they are made to exist, should be produced by incorporating minor changes upon these fundamental forms. The narrowness of the limits in which the creative power must move, unless the whole order of natural forces be changed, would compel such similarity in h results as to create difficulties in classification. r Such perplex1 See North British Review, Vol. xlvi.a p. 308. 2 See Methods of Study in Natural H 5, istory, p. 36.

ities occur in the inorganic, as well as in the organic,world. Increase of knowledge has augmented the difficulty of distinguishing metals from metalloids, and an acid from a base. In crystallography there are only a few fundamental forms; but these forms shade off into one another through insensible gradations. The patent office is a standing illustration of the difficulty of distinguishing objects which have originated in separate acts, but under similar mechanical laws, and for similar ends. For instance, there are three forms of bridges suspension, girder, and arch. These forms are determined by mechanical laws. The girder is intermediate between the other two kinds, and innumerable varieties are possible and actual, which it is not easy to assign to their proper class. What one would call "a stiffened arch," another would denominate a "girder of a peculiar form"; "a third man calls a bridge a strengthened girder, which a fourth says differs in no practical way from a suspension-bridge." This intermingling of forms in the classification of bridges arises from the fact that "there are only certain ways in which a stream can be bridged; the extreme cases are easily perceived, and ingenuity can then only fill in an indefinite number of intermediate varieties." Lawyers have a similar difficulty in determining whether a "particular

1 North British Review, Vol. xlvi. p. 311.

1

case falls under a particular statute," or "is ruled by this or that precedent." In so simple a matter as that of docketing letters or cataloguing books the same perplexities arise. "How difficult it is to devise headings, and how difficult afterwards to know under what head to place your book." 1

It must be confessed that this line of objection has great apparent force, as directed against one of the supposed positive arguments adduced in support of Darwinism. If the theory were largely dependent for its proof upon considerations of this nature, these objections would be more in point. But the Darwinian is free to say, first, that the considerations adduced above do not disprove his hypothesis. The gradations in the classifications of animals and plants are certainly not incompatible with the theory of their common descent. This hypothesis more definitely explains the gradation than any other; and the extent to which the Creator has restricted himself in the possible combinations of elementary matter is not known. Secondly, it is not the bare fact of gradation upon which reliance is had in proof of the Darwinian theory; but it is, rather, upon the method in which one group of species clusters around another group, together with the manner in which these are distributed both through time and space, and the tenacity with which organs

'North British Review, Vol. xlvi. p. 312.