If the creative thought has been expressed by the forms of matter, the laws of thought must be thus expressed in the relative forms of matter. Anything less than this, while it might interpret isolated ideas, would not communicate the method of the creative process, and science is nothing but the discovery of this method. If the terms of the logical process must be arranged in a series, the physical symbols rendering this logical process cognizable, must be arranged in a similar series, for science becomes impossible when the logical process becomes undiscoverable.
The differences between the terms in this series must be cognizable. Two terms which are indistinguishable are practically identical; and two terms which are not identical vary by a difference which is cognizable by itself apart from either term. The steps in the logical evolution of the final term. Being must be separable to be cognizable, and the material forms interpreting these steps to the senses must also be distinguishable. A species differs from the genus by the addition of at least one attribute. Now, if the species is distinguishable from the genus, the attribute which differentiates it, must be separately cognizable—so also the individual differs from the species by the addition of attributes, which must in like manner be separately cognizable, or the species will never be conceived independently of the individuals. A thought cannot proceed by insensible steps, nor can its material expression vary otherwise than by determinate and distinguishable differences. The distinction of species is thus a logical necessity. The addition of distinct attributes to the genus gives origin to distinct species; variation in attributes not affecting their substantial identity gives rise to varieties. One species, then, cannot become another, except by the assumption of a new specific attribute, so that one species passes into another precisely as the genus passes into the species, and that is just as, and not otherwise, than one thought passes into another.
The fundamental law of the logical process is that we pass from the generic towards the individual; from the simple to the complex. Induction can proceed only by assuming a genus at the outset—that is, by assuming certain attributes in the individual to be generic. Translate this law into material forms, and we have each higher—that is more complex—species evolved from the lower by the addition of some new characteristic. This new attribute cannot be added by the functional activity of the lower organism; that can only reproduce itself. A thought does not change merely through repeated expression. We pass to the conclusion of a syllogism, not from each term, but from a comparison of the premises—and this requires an intellectual operation entirely distinct from a mere apprehension of the terms. It is one thing to comprehend the premises; it is quite another to deduce a conclusion from them. It may necessarily follow, but it requires a separate act of the mind to reach it. Premises will not of themselves reach a conclusion.
Reading this same truth in the forms of matter, we may say that species will not pass into higher species without the intervention of a force distinct from either. The impulse which adds a new attribute must be intellectually separable from all those pre-existing, and its material representation must be physically distinct from pre-existing forms. This complete separability precludes the possibility of mere physical genesis. The added attribute is presented by a new form of matter, revealing the presence of a new thought—a new effect, requiring the agency of a new cause. In accordance with the usual economy of nature, who never duplicates her forces, change will be made only so far as may be necessary to communicate the additional idea. Organisms representing previous thoughts will be added to, in order to express the expansion of the thought, instead of a creation de novo in each instance. Thus an identical cellular structure will be found in all organic beings, from the lowest to the highest, each higher type carrying forward the idea and its physical expression found in the lower. The differences between no two terms in the series can be total, nor can any two terms be identical, as each higher species will embrace all the attributes of the lower, differing only by the addition of others. This is simply the physical expression of the logical truth that whatever can be predicated of the genus can be predicated of every individual contained under it. As the individual is only the expansion of the genus, so higher physical types must also be similar expansions of lower.
Here, then, is evolution, or development: primarily an evolution of the generic into the individual, the continued differentiation of a generic idea through successive individualizations, each adding to the previous group of attributes, thus rendering the idea increasingly complex; and, secondly, an apparent physical evolution or development, interpreting this logical process by a series of physical forms so related as to reveal the relation existing between the thoughts thus interpreted. In the physical representation of the ideas so related, there must be an apparent physical evolution—that is, the process of evolution logically must, like the ideas thus evolved, have a physical expression, and the successive steps in this logical evolution must be revealed by material forms bearing an analogous relation, and thereby expressing the logical process. Matter is nothing, so far as we are now concerned, but the condition necessary to the objective expression of thought. Every phase of matter is simply an objective formulation of a corresponding phase of thought. Every addition to form implies an antecedent increase of thought, as there can be no formal expression until there is something to be expressed. There can, then, be no such thing as mere material evolution, for whatever is material is only symbolical.
Matter being thus wholly inert, the origin of the impulse towards greater complexity must be sought for outside of that which undergoes the change. The movement by which one species becomes a higher is not an elaboration, an extension or a differentiation of existing attributes, but involves the positive addition of a new attribute, different and distinct from any or all previously existing. One species cannot pass into another by an innate impulse, for a species is an entity composed of a determinate number of attributes, and all attributes potentially present must be considered as actually present. We cannot say that the child is a different species from the man, and that one passes into the other by a process of evolution, because all the essential attributes of the man are potentially present in the child. If the polyp, by the action of innate forces, operating through a series of ages, however extended, can, without any impulse from without, develop itself into a man, then the polyp is as much a man as a boy is, differing only in the time required for development: and the data for the final deduction of the highest types of creation must be furnished in the most elementary forms of life.
The force manifesting itself in organic life is readily distinguishable from the organism by which it is manifested. Life and organization are not synonyms; one is the condition of the other, but a condition is not a cause. We can consider force apart from organism, and this possible separation in thought proves that the same form may not represent both, but that life can absolutely exist apart from organs which serve to give it a physical manifestation.[3] Physical life being conditioned upon organization, whenever the organism varies, the vital force thus manifested must also vary, such variation being necessarily antecedent to its manifestation. The organism varies, because it must, in order to express the added thought. Change in organism, therefore, is not induced by simple organic action, because the organs and the force acting through them can be distinguished. Assuming that matter is the objective or formal representation of thought, there can be no change in the material expression without a corresponding change in the antecedent conception. There can, then, be physical evolution, only as there is antecedent logical evolution, and then only because of this logical evolution and not because of the operation of an innate organic force. Force, whatever may be its genesis, is only the exertion of power, not the increase of it. Exertion limits the view to the force immediately in operation. We may replace one manifestation by another, but the quantity is neither increased nor diminished by this change. Change in form implies the operation of force: and apart from such manifestation in matter, it escapes the tests of science, and passes into the purely metaphysical notion of cause. And unless the operation of force be constant, or, if different forces are blended, variable according to some determinate law, the action of which is constant and discoverable, so that the different units of force are separately measurable, the force thus irregular in its action can never be placed in any scientific category. Evolution, then, cannot proceed from any innate organic impulse, unless the force that tends to exact reproduction, and the force that induces a change be equally and separately cognizable. Change must proceed according to some law which accounts for the change, and distinguishes between the normal exertion of power and that exertion which causes a deviation. Science, to be science, must explain apparent exceptions as fully as the regular operation of forces, and that which causes the irregularity must be as distinctly cognizably by itself as the force which acts regularly. Anything less than this is not science. The discovery of Neptune was the result of the application of this principle; it was a successful attempt to discriminate the force which caused variation from the force which operated regularly.
Each species represents the operation of certain vital forces, and one cannot physically pass into another except by the increase of this force, or at least by a change in the manner of its manifestation; and this increase in amount or this change in direction must separately be accounted for. Nor does it matter, for the purposes of this discussion, as to the genesis of this added increment, further than to show that its origin must be exterior to the organism by which its presence is manifested; for vital energy acting through an organism is a unit, and cannot, even in thought, be separated into distinguishable portions. Change in the direction of vital energy indicates that the original impulse has been modified in its action by encountering another force, for nothing but force can change the direction of force. It does not fall within the range of this paper to determine the nature of this exterior force which is thus distinguishable from that acting through the vital organization, and therefore capable of separate objective representation. Metaphysically we may say that force is resolvable into will, but will being purely personal is incapable of material representation, and thus cannot enter into the determinations of physical science, which does not seek to discover the origin of force, but deals solely with its presence.
As the logician must assume his premises, and, as a logician, cannot question their truth, so the physicist must assume a force in operation, and, as a physicist, cannot examine its genesis. The physical or the metaphysical method of inquiry is valid only so long as restricted to physical or metaphysical processes: a mixture of the two methods will give results satisfactory neither to science nor to philosophy. As logic furnishes no criterion by which to test the absolute truth of propositions, but deals wholly with conclusions drawn from given premises, so science furnishes no data by which to determine the absolute genesis of force, but restricts its enquiries to the phenomena resulting from a force given. For the student of physical science cause and effect is only the transference of a given and determined force from one material form to another. If this idea is to be traced further, it must be studied outside the limits of physics. This study belongs to metaphysics.
Now, if physical science does not deal with the origin of the initial force, but assumes at the outset its presence, no more does it fall within its province to examine into the origin of the increments which give to physical forms that variety which renders science possible. Science deals with results, not antecedents; and after having determined results, it is not authorized to affirm that one species has produced another by evolution, or has produced it at all. If there are agreements between different organisms by which they are brought into relation, there are also differences by which they are discriminated, and these differences imply increments of force; and to assert that one organism has evolved another is to determine not merely the presence of this new increment, but also to determine its origin. Scientific investigation deals with phenomena which give evidence to the senses of a transference of force from one form or from one manifestation to another. Transference is not increase—an effect can be no more than the evolution of what was potentially present in the cause; it cannot add to it. The origin of the force must be investigated according to intellectual laws.