But the idea of design has a very great significance and application in the organic world. We do undeniably perceive a purpose in the structure and in the life of an organism. The plant and the animal seem to be controlled by a definite design in the combination of their several parts, just as clearly as we see in the machines which man invents and constructs; as long as life continues the functions of the several organs are directed to definite ends, just as is the operation of the various parts of a machine. Hence it was quite natural that the older naïve study of nature, in explaining the origin and activity of the living being, should postulate a creator who had “arranged all things with wisdom and understanding,” and had constructed each plant and animal according to the special purpose of its life. The conception of this “almighty creator of heaven and earth” was usually quite anthropomorphic; he created “everything after its kind.” As long as the creator seemed to man to be of human shape, to think with his brain, see with his eyes, and fashion with his hands, it was possible to form a definite picture of this “divine engineer” and his artistic work in the great workshop of creation. This was not so easy when the idea of God became refined, and man saw in his “invisible God” a creator without organs—a gaseous being. Still more unintelligible did these anthropomorphic ideas become when physiology substituted for the conscious, divine architect an unconscious, creative “vital force”—a mysterious, purposive, natural force, which differed from the familiar forces of physics and chemistry, and only took these in part, during life, into its service. This vitalism prevailed until about the middle of the nineteenth century. Johannes Müller, the great Berlin physiologist, was the first to menace it with a destructive dose of facts. It is true that the distinguished biologist had himself (like all others in the first half of the century) been educated in a belief in this vital force, and deemed it indispensable for an elucidation of the ultimate sources of life; nevertheless, in his classical and still unrivalled Manual of Physiology (1833) he gave a demonstrative proof that there is really nothing to be said for this vital force. Müller himself, in a long series of remarkable observations and experiments, showed that most of the vital processes in the human organism (and in the other animals) take place according to physical and chemical laws, and that many of them are capable of mathematical determination. That was no less true of the animal functions of the muscles and nerves, and of both the higher and the lower sense-organs, than of the vegetal functions of digestion, assimilation, and circulation. Only two branches of the life of the organism, mental action and reproduction, retained any element of mystery, and seemed inexplicable without assuming a vital force. But immediately after Müller’s death such important discoveries and advances were made in these two branches that the uneasy “phantom of vital force” was driven from its last refuge. By a very remarkable coincidence Johannes Müller died in the year 1858, which saw the publication of Darwin’s first communication concerning his famous theory. The theory of selection solved the great problem that had mastered Müller—the question of the origin of orderly arrangements from purely mechanical causes.

Darwin, as we have often said, had a twofold immortal merit in the field of philosophy—firstly, the reform of Lamarck’s theory of descent, and its establishment on the mass of facts accumulated in the course of the half-century; secondly, the conception of the theory of selection, which first revealed to us the true causes of the gradual formation of species. Darwin was the first to point out that the “struggle for life” is the unconscious regulator which controls the reciprocal action of heredity and adaptation in the gradual transformation of species; it is the great “selective divinity” which, by a purely “natural choice,” without preconceived design, creates new forms, just as selective man creates new types by an “artificial choice” with a definite design. That gave us the solution of the great philosophic problem: “How can purposive contrivances be produced by purely mechanical processes without design?” Kant held the problem to be insoluble, although Empedocles had pointed out the direction of the solution two thousand years before. His principle of “teleological mechanism” has become more and more accepted of late years, and has furnished a mechanical explanation even of the finest and most recondite processes of organic life by “the functional self-production of the purposive structure.” Thus have we got rid of the transcendental “design” of the ideological philosophy of the schools, which was the greatest obstacle to the growth of a rational and monistic conception of nature.

Very recently, however, this ancient phantom of a mystic vital force, which seemed to be effectually banished, has put in a fresh appearance; a number of distinguished biologists have attempted to reintroduce it under another name. The clearest presentation of it is to be found in the Welt als That, of the Kiel botanist, J. Reinke. He takes upon himself the defence of the notion of miracle, of theism, of the Mosaic story of creation, and of the constancy of species; he calls “vital forces,” in opposition to physical forces, the directive or dominant forces. Other neovitalists prefer, in the good old anthropomorphic style, a “supreme” engineer, who has endowed organic substance with a purposive structure, directed to the realization of a definite plan. These curious teleological hypotheses, and the objections to Darwinism which generally accompany them, do not call for serious scientific refutation to-day.

Thirty-three years ago I gave the title of “dysteleology” to the science of those extremely interesting and significant biological facts, which, in the most striking fashion, give a direct contradiction to the teleological idea “of the purposive arrangement of the living organism.”[30] This “science of rudimentary, abortive, arrested, distorted, atrophied, and cataplastic individuals” is based on an immense quantity of remarkable phenomena, which were long familiar to zoologists and botanists, but were not properly interpreted, and their great philosophic significance appreciated, until Darwin.

All the higher animals and plants, or, in general, all organisms which are not entirely simple in structure, but are made up of a number of organs in orderly co-operation, are found, on close examination, to possess a number of useless or inoperative members, sometimes, indeed, hurtful and dangerous. In the flowers of most plants we find, besides the actual sex-leaves that effect reproduction, a number of other leaf-organs which have no use or meaning (arrested or “miscarried” pistils, fruit, corona, and calix-leaves, etc.). In the two large and variegated classes of flying animals, birds and insects, there are, besides the forms which make constant use of their wings, a number of species which have undeveloped wings and cannot fly. In nearly every class of the higher animals which have eyes there are certain types that live in the dark; they have eyes, as a rule, but undeveloped and useless for vision. In our own human organism we have similar useless rudimentary structures in the muscles of the ear, in the eye-lid, in the nipple and milk-gland of the male, and in other parts of the body; indeed, the vermiform appendix of our cæcum is not only useless, but extremely dangerous, and inflammation of it is responsible for a number of deaths every year.

Neither the old mystic vitalism nor the new, equally irrational, neovitalism can give any explanation of these and many other purposeless contrivances in the structure of the plant and the animal; but they are very simple in the light of the theory of descent. It shows that these rudimentary organs are atrophied, owing to disuse. Just as our muscles, nerves, and organs of sense are strengthened by exercise and frequent use, so, on the other hand, they are liable to degenerate more or less by disuse or suspended exercise. But, although the development of the organs is promoted by exercise and adaptation, they by no means disappear without leaving a trace after neglect; the force of heredity retains them for many generations, and only permits their gradual disappearance after the lapse of a considerable time. The blind “struggle for existence between the organs” determines their historical disappearance, just as it effected their first origin and development. There is no internal “purpose” whatever in the drama.

The life of the animal and the plant bears the same universal character of incompleteness as the life of man. This is directly attributable to the circumstance that nature—organic as well as inorganic—is in a perennial state of evolution, change, and transformation. This evolution seems on the whole—at least as far as we can survey the development of organic life on our planet—to be a progressive improvement, an historical advance from the simple to the complex, the lower to the higher, the imperfect to the perfect. I have proved in my General Morphology that this historical progress—or gradual perfecting (teleosis)—is the inevitable result of selection, and not the outcome of a preconceived design. That is clear from the fact that no organism is perfect; even if it does perfectly adapt itself to its environment at a given moment, this condition would not last very long; the conditions of existence of the environment are themselves subject to perpetual change and they thus necessitate a continuous adaptation on the part of the organism.

Under the title of Design in the Living Organism, the famous embryologist, Karl Ernst Baer, published a work in 1876 which, together with the article on Darwinism which accompanied it, proved very acceptable to our opponents, and is still much quoted in opposition to evolution. It was a revival of the old teleological system under a new name, and we must devote a line of criticism to it. We must premise that, though Baer was a scientist of the highest order, his original monistic views were gradually marred by a tinge of mysticism with the advance of age, and he eventually became a thorough dualist. In his profound work on “the evolution of animals” (1828), which he himself entitled Observation and Experiment, these two methods of investigation are equally applied. By careful observation of the various phenomena of the development of the animal ovum Baer succeeded in giving the first consistent presentation of the remarkable changes which take place in the growth of the vertebrate from a simple egg-cell. At the same time he endeavored, by far-seeing comparison and keen reflection, to learn the causes of the transformation, and to reduce them to general constructive laws. He expressed the general result of his research in the following thesis: “The evolution of the individual is the story of the growth of individuality in every respect.” He meant that “the one great thought that controls all the different aspects of animal evolution is the same that gathered the scattered fragments of space into spheres and linked them into solar systems. This thought is no other than life itself, and the words and syllables in which it finds utterance are the varied forms of living things.”

Baer, however, did not attain to a deeper knowledge of this great genetic truth and a clearer insight into the real efficient causes of organic evolution, because his attention was exclusively given to one half of evolutionary science, the science of the evolution of the individual, embryology, or, in a wider sense, ontogeny. The other half, the science of the evolution of species, phylogeny, was not yet in existence, although Lamarck had already pointed out the way to it in 1809. When it was established by Darwin in 1859, the aged Baer was no longer in a position to appreciate it; the fruitless struggle which he led against the theory of selection clearly proved that he understood neither its real meaning nor its philosophic importance. Teleological and, subsequently, theological speculations had incapacitated the ageing scientist from appreciating this greatest reform of biology. The teleological observations which he published against it in his Species and Studies in his eighty-fourth year are mere repetitions of errors which the teleology of the dualists has opposed to the mechanical or monistic system for more than two thousand years. The “telic idea” which, according to Baer, controls the entire evolution of the animal from the ovum, is only another expression for the eternal “idea” of Plato and the entelecheia of his pupil Aristotle.

Our modern biogeny gives a purely physiological explanation of the facts of embryology, in assigning the functions of heredity and adaptation as their causes. The great biogenetic law, which Baer failed to appreciate, reveals the intimate causal connection between the ontogenesis of the individual and the phylogenesis of its ancestors; the former seems to be a recapitulation of the latter. Nowhere, however, in the evolution of animals and plants do we find any trace of design, but merely the inevitable outcome of the struggle for existence, the blind controller, instead of the provident God, that effects the changes of organic forms by a mutual action of the laws of heredity and adaptation. And there is no more trace of “design” in the embryology of the individual plant, animal, or man. This ontogeny is but a brief epitome of phylogeny, an abbreviated and condensed recapitulation of it, determined by the physiological laws of heredity.