CHAPTERS ON EVOLUTION.

I.

THE PROBLEM STATED.

THE year 1858 may be said to mark a distinct era in the science of biology, or that dealing with the structure, functions, development, and general history of animals and plants. On July 1, 1858, two papers were read before the Linnæan Society of London, which were destined to evoke and to direct an amount of criticism and research unparalleled in the annals of scientific history. It was then that Mr. Darwin and Mr. Alfred Russel Wallace laid before the scientific world the results of independent observations and reflections concerning the origin of the varied species of animals and plants which form the diverse population of the globe. Considering that the views expressed in the papers referred to had been formed and elaborated in entire independence of thought, and, indeed, in well-nigh opposite regions of the earth's surface, the harmonious nature of the conclusions arrived at by the authors was both interesting and surprising. Mr. Darwin's paper dealt with the Origin of Species; that of Mr. Wallace bore the title "On the Tendency of Varieties to depart indefinitely from the Original Type." The former, as naturalist on board H.M.S. "Beagle," had been "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." Mr. Darwin further tells us that "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." Mr. Wallace, on the other hand, exploring the Malay Archipelago, and interesting himself in the problems which the varied flora and fauna of the East suggested to the mind, formed opinions concerning the origin of species which, as we have seen, practically coincided with those of Darwin. In each case the inspiration, so to speak, came direct from nature, and from the unbiassed observation of the world of life itself an origin this, as suggestive as it was appropriate for speculations including in their sweep and extent the entire organic universe.

B

The leading ideas of 1858 may be briefly and plainly stated. Mr. Wallace's conclusion may be summed up in his own expression, " that there is a tendency in nature to the continued progression of certain classes of varieties further and further from the original type-a progression to which there appears no reason to assign any definite limits—and that the same principle which produces this result in a state of nature will also explain why domestic varieties have a tendency, when they become wild, to revert to the original type. This progression," continues Mr. Wallace, "by minute steps in various directions, but always checked and balanced by the necessary conditions, subject to which alone existence can be preserved, may, it is believed, be followed out so as to agree with all the phenomena presented by organised beings, their extinction and succession in past ages, and all the extraordinary modifications of form, instinct, and habits which they exhibit." Mr. Darwin's views were no less lucidly expressed. He agreed essentially with Mr. Wallace in attributing the origin of new species to the modification of already existent animals and plants. The "Origin of Species" itself—a work first published in November 1859, and at present in its "thirteenth thousand "—represents the expansion and elaboration of Mr. Darwin's views of 1858, the publication of which raised at once a multitude of scientific critics, and invoked, it may be added, the rancour, bigotry, and often insensate, because ignorant, opposition of many persons outside the ranks of biological science.

To understand the meaning of the opposition which the views of Darwin and Wallace at first provoked, it is needful simply to take a brief retrospective view of the history of man's ideas regarding the origin of living nature, including, of course, the history of his own genesis. The opinions of 1858 were at first simply branded with the heterodox stamp, as preceding opinions had been similarly treated from the time of Lamarck in 1801, and, indeed, as every other statement which was not thoroughly "nail'd wi' Scriptur'," had been treated with the "apostolic blows and knocks" of those who seemed to claim a monopoly of all truth concerning the past, present, and future of the universe. The reason for the stormy reception of views concerning the species of animals and plants, promulgated as a matter of strict science, and formulated without any reference to other or more venerable opinions, can be readily enough understood, when it is added that the chief opposition to the Origin of Species" came from the theological camp. Mr. Spencer remarks that "early ideas are not usually true ideas." He might have added with equal truth that early ideas, when woven into the texture of religious systems, are not given to lose their vitality with increasing age. At all events, the opposition to the views of Darwin, and to the evolution theory at large, were chiefly combated,

not from any inherent error they were believed to contain, but simply because they ran in direct opposition to the older and more primitive conceptions of the origin of species which, formulated in creeds, and elaborated from pulpits, had come to be received as an article of unquestioning faith by cultured and uncultured alike. Two theories, and only two, concerning the origin of animals and plants, present themselves for examination and acceptation by the human intellect. Of these two theories, one dates from a pre-scientific period, when this earth was believed to be the centre of the universe, when this world was believed to possess a round and flattened surface, and when the sky was believed to be a solid roof environing the earth above, and constituting at the same time the floor of an upper and celestial sphere. Such rude ideas of cosmogony and astronomy were fully paralleled by as primitive a biological system. The various species of animals and plants were believed, according to the Mosaic cosmogony, to have originated each as a complete and "special creation." As man was conceived to have been formed of the dust of the earth, and as all the intricacies and complexities, structural, physical, and chemical, of the human organism were believed to have been set in action at once and perfectly, through the operation of a mysterious, supernatural fiat; so the varied species of animals and plants, from the monad to the elephant, from the plantspecks in the pool to the giant pine or lordly oak, were similarly held to have originated each as a "special creation." In this way a creative interference, capable of originating living beings ex nihilo, and therefore capable of literally creating matter-itself an inconceivable act-was credited on the first theory, as it may still be credited in creed and dogma, with the production of the entire universe of living things.

The genesis and development of such a theory has naturally been laid stress upon by most writers who have criticised, from an a priori point of view, the worthiness and acceptation of itself and its opponent hypothesis. The fact that the "special creation" theory was framed in an age when primitive ideas and mythologies, now completely consigned to the limbo reserved for exploded myths, constituted the philosophy of mankind, naturally militates against the truth and probability of the hypothesis in question. Being a primitive imagining, it would, according to Mr. Spencer's view, be most likely a wrong and untrue one. "If the interpretations of nature given by aboriginal men were erroneous in other directions," says that author, "they were most likely erroneous in this direction. It would be strange if, whilst these aboriginal men failed to reach the truth in so many cases where it is comparatively conspicuous, they yet reached the truth in a case where it is comparatively hidden." As we have to-day rejected the astronomy of the

ancients, and as we no longer utilise their geology as serviceable or true, we can afford to dispense with their biological views, and we therefore turn hopefully to the second and scientific conception of the origin of living beings. This conception is the theory of "Derivation," "Descent," or Evolution."

According to the evolutionist, the universe of life, instead of being composed of a series of fixed and unchangeable units— unvarying as when they were first "created" on the former theory of life's origin is the theatre of incessant variation and change. Each "species" or "kind" of animals and plants, instead of existing as a stable unvarying group, as the older naturalists defined it, is seen to vary to a greater or less degree, according to internal and constitutional, or to external conditions, or under the influence of both combined. The progeny do not rigidly resemble the parents, but continually exhibit differences in colour, size, and other peculiarities. Thus "variations" in species are produced; and these variations may appear of singularly wide character when conditions favouring change have operated in their production. In this way the existing "species" are modified, and the new "varieties " thus produced, in time give origin to new species. These latter are, therefore, viewed as having been "evolved" by natural descent, that is by the ordinary laws of generation and reproduction, from the older species. The animal and plant worlds regarded in this light are liable to perpetual modification, and the experience of every-day life-seen familiarly in the culture of plants, and in the breeding of horses, cattle, sheep, dogs, and pigeons-amply testifies to the mobility and plasticity of the animal and plant constitutions. That is to say, man, in the process of breeding animals, and by selecting the parents of his domestic races, can "evolve" animals which, in time, differ from the original stock far more widely than ordinary and so-called "species" differ from one another.

But the plasticity of "species" is far from being the only prop and support of the theory of evolution. When the naturalist attempts to classify animals or plants, he discovers that instead of exhibiting each a specific and individualised structure, as might be presumed were the "special creation" theory true, the various groups of animals are linked together in such a fashion as to suggest the existence of some natural bond of relationship between them. With the plant world the case is analogous. The tribes of plants are harmoniously connected together in such a manner as to indicate a relationship which, as in the case of the animals, is only satisfactorily explained on the idea of connected descent. What explanation, for example, satisfying to the rational mind, can be given of such a striking feature as that illustrated in the literally marvellous correspondence which exists between the fore and hind

limbs respectively of all vertebrate animals? How, on any other hypothesis save that of evolution, and of the common origin of the animals in question, can we explain why the arm of man, the wing of the bird, the horse's fore-limb, the dog's fore-leg, and the whale's paddle, are constructed on a common plan? Or, again, why should the bodies and appendages of lobsters, insects, spiders, and centipedes, be similarly identical in fundamental structure, unless on the theory of their common origin?

Again, from the region of Development, the evolutionist derives a whole host of cogent reasons for the faith he entertains in the soundness of his conclusions. All animals begin life under a similar guise— or, to come to actual details, as protoplasmic specks. In their earliest stages, the germs of a man and of an animalcule are indistinguishable. Furthermore, as human development proceeds along its lines, it assumes its own and special phases only after passing through stages which correspond more or less completely with permanent forms of lower animals. At first each quadruped is thus fish-like, and after successive developments leading it upwards through reptile and bird phases, it attains the quadruped type. But, even as a quadruped, the human organism itself declares its nobility of blood, only as a final feature in its early history. Of all other animals, the same recital holds good. Each animal comes to assume its own place as an adult through stages of development which repeat, as in a moving panorama, the phases of the lower life through which its ancestry has passed. The development of the individual animal is thus the brief and condensed recapitulation, often more or less obscured, of the development of the race or species. If facts like these be not admitted to prove the reality of evolution, then development as a whole must present itself as a series of the most meaningless paradoxes which it has been the fate of man to discover in the universe around.

Such are a few of the considerations-to be fully illustrated in succeeding chapters-which suggest that evolution is a great truth and a sober fact of living nature. Other topics of equal importance -such as the occurrence of rudimentary and useless organs in animals and plants, the existence of "links" between distinct groups, the results of degeneration, and other subjects-will also be found fully detailed in the following pages, which partake, indeed, of the character of a continuous series of proofs of the truth of the evolution theory. It requires, however, to be pointed out in the present instance, that whilst the general truth of evolution is now admitted by all competent biologists, there exists considerable diversity of opinion regarding the exact factors to which the processes of modification are due. Thus the title of Mr. Darwin's classic work is "The Origin of Species by Means of Natural Selection; or, the