Note (return) — Chapter VI

The "true naturalist," therefore, recognizes two great principles pervading the universe--a principle of order--a unity of plan, and a principle of special adaptation, by which each object, though constructed upon a general plan, is at the same time accommodated to the place it has to occupy and the purpose it has to serve. In other words, there is homology of structure and analogy of function, conformity to archetypal forms and Teleology of organs, in wonderful combination. Now, in the Materialistic school, it has been the prevalent practice to set up the unity of plan in animal structures, in opposition to the principle of Final Causes: Morphology has been opposed to Teleology. But in nature there is no such opposition; on the contrary, there is a beautiful co-ordination. The same bones, in different animals, are made subservient to the widest possible diversity of functions. The same limbs are converted into fins, paddles, wings, legs, and arms. "No comparative anatomist has the slightest hesitation in admitting that the pectoral fin of a fish, the wing of a bird, the paddle of the dolphin, the fore-leg of a deer, the wing of a bat, and the arm of a man, are the same organs, notwithstanding that their forms are so varied, and the uses to which they are applied so unlike each other." 270 All these are homologous in structure--they are formed after an ideal archetype or model, but that model or type is variously modified to adapt the animal to the sphere of life in which it is destined to move, and the organ itself to the functions it has to perform, whether swimming, flying, walking, or burrowing, or that varied manipulation of which the human hand is capable. These varied modifications of the vertebrated type, for special purposes, are unmistakable examples of final causation. Whilst the silent members, the rudimental limbs instanced by Oken, Martins, and others--as fulfilling no purpose, and serving no end, exist in conformity to an ideal archetype on which the bony skeletons of all vertebrated animals are formed, 271 and which has never been departed from since time began. This type, or model, or plan, is, however, itself an evidence of design as much as the plan of a house. For to what standard are we referring when we say that two limbs are morphologically the same? Is it not an ideal plan, a mental pattern, a metaphysical conception? Now an ideal implies a mind which preconceived the idea, and in which alone it really exists. It is only as "an order of Divine thought" that the doctrine of animal homologies is at all intelligible; and Homology is, therefore, the science which traces the outward embodiment of a Divine Idea. 272 The principle of intentionality or final causation, then, is not in any sense invalidated by the discovery of "a unity of plan" sweeping through the entire universe.