Definition of species-Special creation-The early Transmutationists— Scientific opinion before Darwin-The problem before Darwin— The change of opinion effected by Darwin-The Darwinian theory -Proposed mode of treatment of the subject.

THE title of Mr. Darwin's great work is-On the Origin of Species by means of Natural Selection and the Preservation of Favoured Races in the Struggle for Life. In order to appreciate fully the aim and object of this work, and the change which it has effected not only in natural history but in many other sciences, it is necessary to form a clear conception of the meaning of the term "species," to know what was the general belief regarding them at the time when Mr. Darwin's book first appeared, and to understand what he meant, and what was generally meant, by discovering their "origin." It is for want of this preliminary knowledge that the majority of educated persons who are not naturalists are so ready to accept the innumerable objections, criticisms, and difficulties of its opponents as proofs that the Darwinian theory is unsound, while it also renders them unable to appreciate, or even to comprehend, the vast change which that theory has effected in the whole mass of thought and opinion on the great question of evolution.

The term "species" was thus defined by the celebrated botanist De Candolle: "A species is a collection of all the individuals which resemble each other more than they resemble anything else, which can by mutual fecundation

B

produce fertile individuals, and which reproduce themselves by generation, in such a manner that we may from analogy suppose them all to have sprung from one single individual.” And the zoologist Swainson gives a somewhat similar definition: "A species, in the usual acceptation of the term, is an animal which, in a state of nature, is distinguished by certain peculiarities of form, size, colour, or other circumstances, from another animal. It propagates, 'after its kind,' individuals perfectly resembling the parent; its peculiarities, therefore, are permanent.

To illustrate these definitions we will take two common English birds, the rook (Corvus frugilegus) and the crow (Corvus corone). These are distinct species, because, in the first place, they always differ from each other in certain slight peculiarities of structure, form, and habits, and, in the second place, because rooks always produce rooks, and crows produce crows, and they do not interbreed. It was therefore concluded that all the rooks in the world had descended from a single pair of rooks, and the crows in like manner from a single pair of crows, while it was considered impossible that crows could have descended from rooks or vice versa.

The

'origin of the first pair of each kind was a mystery. Similar remarks may be applied to our two common plants, the sweet violet (Viola odorata) and the dog violet (Viola canina). These also produce their like and never produce each other or intermingle, and they were therefore each supposed to have sprung from a single individual whose origin" was unknown. But besides the crow and the rook there are about thirty other kinds of birds in various parts of the world, all so much like our species that they receive the common name of crows; and some of them differ less from each other than does our crow from our rook. These are all species of the genus Corvus, and were therefore believed to have been always as distinct as they are now, neither more nor less, and to have each descended from one pair of ancestral crows of the same identical species, which themselves had an unknown "origin." Of violets there are more than a hundred different kinds in various parts of the world, all differing very slightly from each other and forming distinct 1 Geography and Classification of Animals, p. 350.

species of the genus Viola. But, as these also each produce their like and do not intermingle, it was believed that every one of them had always been as distinct from all the others as it is now, that all the individuals of each kind had descended from one ancestor, but that the "origin" of these hundred slightly differing ancestors was unknown. In the words of Sir John Herschel, quoted by Mr. Darwin, the origin of such species was "the mystery of mysteries."

The Early Transmutationists.

A few great naturalists, struck by the very slight difference between many of these species, and the numerous links that exist between the most different forms of animals and plants, and also observing that a great many species do vary considerably in their forms, colours, and habits, conceived the idea that they might be all produced one from the other. The most eminent of these writers was a great French naturalist, Lamarck, who published an elaborate work, the Philosophie Zoologique, in which he endeavoured to prove that all animals whatever are descended from other species of animals. He attributed the change of species chiefly to the effect of changes in the conditions of life-such as climate, food, etc.and especially to the desires and efforts of the animals themselves to improve their condition, leading to a modification of form or size in certain parts, owing to the well-known physiological law that all organs are strengthened by constant use, while they are weakened or even completely lost by disuse. The arguments of Lamarck did not, however, satisfy naturalists, and though a few adopted the view that closely allied species had descended from each other, the general belief of the educated public was, that each species was a "special creation" quite independent of all others; while the great body of naturalists equally held, that the change from one species. to another by any known law or cause was impossible, and that the "origin of species' was an unsolved and probably insoluble problem. The only other important work dealing with the question was the celebrated Vestiges of Creation, published anonymously, but now acknowledged to have been written by the late Robert Chambers. In this work the action of general laws was traced throughout the

universe as a system of growth and development, and it was argued that the various species of animals and plants had been produced in orderly succession from each other by the action of unknown laws of development aided by the action of external conditions. Although this work had a considerable effect in influencing public opinion as to the extreme improbability of the doctrine of the independent "special creation" of each species, it had little effect upon naturalists, because it made no attempt to grapple with the problem in detail, or to show in any single case how the allied species of a genus could have arisen, and have preserved their numerous slight and apparently purposeless differences from each other. No clue whatever was afforded to a law which should produce from any one species one or more slightly differing but yet permanently distinct species, nor was any reason given why such slight yet constant differences should exist at all.

Scientific Opinion before Darwin.

In order to show how little effect these writers had upon the public mind, I will quote a few passages from the writings of Sir Charles Lyell, as representing the opinions of the most advanced thinkers in the period immediately preceding that of Darwin's work. When recapitulating the facts and arguments in favour of the invariability and permanence of species, he says: "The entire variation from the original type which any given kind of change can produce may usually be effected in a brief period of time, after which no further deviation can be obtained by continuing to alter the circumstances, though ever so gradually, indefinite divergence either in the way of improvement or deterioration being prevented, and the least possible excess beyond the defined limits being fatal to the existence of the individual." In another place he maintains that "varieties of some species may differ more than other species do from each other without shaking our confidence in the reality of species.' He further adduces certain facts in geology as being, in his opinion, "fatal to the theory of progressive development," and he explains the fact that there are so often distinct species in countries of similar climate and vegetation by

"special creations in each country; and these conclusions were arrived at after a careful study of Lamarck's work, a full abstract of which is given in the earlier editions of the Principles of Geology.1

Professor Agassiz, one of the greatest naturalists of the last generation, went even further, and maintained not only that each species was specially created, but that it was created in the proportions and in the localities in which we now find it to exist. The following extract from his very instructive book on Lake Superior explains this view: "There are in animals peculiar adaptations which are characteristic of their species, and which cannot be supposed to have arisen from subordinate influences. Those which live in shoals cannot be supposed to have been created in single pairs. Those which are made to be the food of others cannot have been created in the same proportions as those which live upon them. Those which are everywhere found in innumerable specimens must have been introduced in numbers capable of maintaining their normal proportions to those which live isolated and are comparatively and constantly fewer. For we know that this harmony in the numerical proportions between animals is one of the great laws of nature. The circumstance that species occur within definite limits where no obstacles prevent their wider distribution leads to the further inference that these limits were assigned to them from the beginning, and so we should come to the final conclusion that the order which prevails throughout nature is intentional, that it is regulated by the limits marked out on the first day of creation, and that it has been maintained unchanged through ages with no other modifications than those which the higher intellectual powers of man enable him to impose on some few animals more closely connected with him." 2

These opinions of some of the most eminent and influential writers of the pre-Darwinian age seem to us, now, either altogether obsolete or positively absurd; but they nevertheless exhibit the mental condition of even the most advanced section of scientific men on the problem of the

1 These expressions occur in Chapter IX. of the earlier editions (to the ninth) of the Principles of Geology.

2 L. Agassiz, Lake Superior, p. 377.