Parallel Paths: A Study in Biology, Ethics, and Art. T. W. Rolleston
Читать онлайн книгу.
evolution theory, based on a study of organic structure. Erasmus Darwin, in 1794, had uttered the great and final word: “The world has been generated rather than created.”5 Lamarck’s Philosophie Zoologique was not published till 1809, nine years after Paley’s Natural Theology, but his conception of the development of special characteristics by habitual exercise and their transmission by inheritance had been freely mooted in Paley’s day, for Paley frequently takes occasion to combat it. Even the conception of natural selection as an agency in the formation of types of being may be traced in a fantastic form as far back as to Empedocles,6 while Plato, or whoever composed a striking couplet attributed to him in the Greek Anthology, had divined the plasticity of natural forms. “Time,” he wrote, “sways the whole world; time has power in its prolonged lapse to change the names and shapes, the nature and the destiny of things.”7
Fifty years after the appearance of Paley’s work, the grandson of Erasmus Darwin wrote ‘No thoroughfare’ on the entrance to Paley’s line of speculation, and closed it to mankind for ever. He did this in two ways—first by marshalling from his studies of comparative anatomy and of embryology an extraordinary volume of convincing evidence for the fact of the mutability of natural forms, and secondly by his attempt to establish a plausible method by which the change and development of organs and types might actually have taken place. The method, summed up in the phrases ‘natural selection’ and ‘survival of the fittest,’ was what really caught the attention of the world, and gave his doctrine the wings which carried it into almost every sphere of human thought. However we take it, it was certainly an immense contribution to the organization of knowledge, but whether it is really what it first seemed to be, the basic fact at the bottom of all the phenomena of evolution, is coming to look more and more doubtful in the light of later researches.8
This question will have to be considered later on in the course of this study, and in relation to its main inquiry, which is this: What precisely was the change in philosophic and religious outlook brought about by the full and final establishment of the doctrine of evolution? Where has evolution left the argument from design? Must we study nature as a mass of unrelated phenomena, or can we discern, through these, any fundamental unity to which they stand in organic relation; and if we can, what is the nature of this unity?
It will be useful in the first place to have before us a typical specimen of Paley’s method. I shall choose as an example the case which he considered so striking that he deemed it almost sufficient in itself to bear the whole weight of his argument In his ninth chapter, ‘On the Muscles,’ he writes:—
“The next circumstance which I shall mention under this head of muscular arrangement is so decisive a mark of intention, that it always appeared to me to supersede, in some measure, the necessity of seeking for any other observation upon the subject; and that circumstance is, the tendons which pass from the leg to the foot being bound down by a ligament to the ankle. The foot is placed at a considerable angle with the leg. It is manifest, therefore, that flexible strings, passing along the interior of the angle, if left to themselves, would, when stretched, start from it. The obvious preventive is to tie them down. And this is done, in fact. Across the instep, or rather just above it, the anatomist finds a strong ligament, under which the tendons pass to the foot. The effect of the ligament as a bandage can be made evident to the senses; for if it be cut, the tendons start up. The simplicity, yet the clearness of this contrivance, its exact resemblance to established resources of art, place it amongst the most indubitable manifestations of design with which we are acquainted. “There is also a further use to be made of the present example, and that is, as it precisely contradicts the opinion that the parts of animals may have been formed by what is called appetency, i.e. endeavour perpetuated and imperceptibly working its effect through an incalculable series of generations. We have here no endeavour but the reverse of it—a constant renitency and reluctance. The endeavour is all the other way. The pressure of the ligament constrains the tendons; the tendons react upon the pressure of the ligament. It is impossible that the ligament should ever have been generated by the exercise of the tendon, or in the course of that exercise, forasmuch as the force of the tendon perpendicularly resists the fibre, which confines it, and is constantly endeavouring not to form, but to rupture and displace, the threads of which the ligament is composed.”
Paley’s account of the function of the annular ligament at the ankle is correct, and strikingly put. A similar ligament occurs at the wrist, and navvies who have hard muscular work to do in digging and shovelling are wont to reinforce this ligament and to keep it from rupture by a leather strap round the wrist. The strap performs exactly the same function as the ligament, and from Paley’s point of view one is as artificial, as much a ‘contrivance,’ as the other. But his point of view is wrong. He conceives the Creator as having at his disposal fully formed elements or materials—sinews, bones, ligaments, and the like—and assembling them into a working mechanism. In fact, however, none of these things is now what it was originally—time, as Plato says, has changed its “name and shape.” The annular ligaments are recognized by modern anatomists as having originated in special thickenings of the fascial sheaths of the adjoining muscles of the wrist and ankle. They had a function which was not originally connected with keeping down the long tendons that run along the interior angle of the leg and foot. Contractility, as biologists tell us, is a fundamental property of living protoplasm; and it is easy to imagine that, at the very beginning of the formation of muscular structure and bone articulation, two lines of contractile force might cross each other and thus permit the gradual evolution of the present arrangement, nature continually visiting with disability and extinction those individuals in whom the resisting power of the muscles which were eventually to form the annular ligament was unduly feeble, and giving a better chance of life, and of the propagation of their kind, to those in whom it was strong. The instance, in fact, is one of those in which the explanation of development by natural selection is most obvious and plausible.
In his second paragraph Paley touches on the theory of “appetency,” the supposed tendency of natural structure to alter and adapt itself on the lines indicated by the actual exercise of function, and in consequence of that exercise. This is practically the theory since identified with the name of Lamarck. Paley scarcely does it justice, for no Lamarckian would suggest that a muscle could, in the course of its exercise, develop the ligament whose function is to restrain it. The ligament would be developed by its own exercise. But as Lamarckism will be discussed later on, the issue as between these rival theories need not be debated here.
Let us set beside Paley’s argument on the annular ligament of the ankle a passage from a modern scientific work, Strasburger’s Text Book of Botany. It will introduce us, from the side of the strictest scientific observation and of the fullest acceptance of the evolution theory, to the same kind of problems as those discussed in Paley’s Natural Theology, and it will raise in a very distinct and unevadable fashion the question, what we are to think of the power manifested in the operations of Nature. In the introduction to his work, in which Dr. Strasburger had associated with him three other eminent German botanists, we find the following remarkable passage dealing with circumstances observed to exist in the ‘phylogenetic’ or tribal (as opposed to the ‘ontogenetic’ or individual) history of plant species:—
“Although the great importance of natural selection in the development of the organic world has been fully recognised by most naturalists, the objection has been raised that it alone is not a sufficient explanation of all the different processes in the phylogeny of an organism. Attention has been called to such organs as would be incapable of exercising their function until in an advanced stage of development, and so could not originally have been of any advantage in a struggle for existence. How could natural selection tend to develop an organ which would be useless so long as it was still in a rudimentary condition? This objection has led to the supposition of an internal force residing in the substance of the organisms themselves and controlling their development in certain definite directions. Many naturalists indeed have gone so far as to affirm that only the less advantageous qualities have been affected by the struggle for existence, while the more advantageous have been uninfluenced by it”9
One can easily imagine what a modern Paley bent on reconciling orthodoxy and evolution would say to this. He would cry, Design, forethought,