If, then, in the intellectual process from the abstract and universal towards the concrete and individual, we find a constant evolution of idea, each advance being an addition to the previous conception, each new term in the series embracing all the attributes of the preceding, and differing only by addition; and if thought is possible only on this condition; it necessarily follows that the material representation of this thought must present physical forms similarly related, so that, leaving out of view the intellectual genesis of this relation, the observer might conclude that these forms compose a series evolved from a primordial cell in accordance with an organic law. But such we find to be the universal law of intellectual procedure: this apparent development or evolution must, therefore, be the condition of the communication of such intellectual process, and the physical terms are brought into this relation by the fact that they symbolize the logical process. If the material symbols of thought were unrelated physically, the thoughts thus expressed would also be unrelated and independent. But such a supposition readers Science impossible, for its one aim is to find the _same_ in the _different_. If there be no _same_, there can be no science: if there be no _different_, there can be no science. Thought proceeds by adding the _different_ to the _same_ in an endless series, and this addition of the _different_ to the _same_ expressed in concrete forms is what is called evolution. If no evolution were apparent in Nature, there could be no Science; for those steps which to the naturalist indicate evolution, being only the physical expression--the formulation--of the logical process, afford the means by which the student reaches the highest generalization. If these steps be wanting, he cannot proceed.