§ 57. Thus we find that to complete the definition arrived at in the last chapter, much has to be added. What was there alleged is true; but it is not the whole truth. Evolution is unquestionably a change from a homogeneous state to a heterogeneous state; but, as we have seen, there are some advances in heterogeneity which cannot be included in the idea of Evolution. This undue width of the definition, implies the omission of some further peculiarity by which Evolution is distinguished; and this peculiarity we find to be that the more highly developed things become, the more definite they become. Advance from the indefinite to the definite, is as constantly and variously displayed as advance from the homogeneous to the heterogeneous. And we are thus obliged to regard it as an essential characteristic of Evolution. Further analysis, however, shows us that this increase of definiteness is not an independent process; but is rather the necessary concomitant of another process. A very little consideration of the facts proves that a change from the indefinite to the definite, can arise only through a completer consolidation of the respective parts, and of the whole which they constitute. And so we find that while Evolution is a transformation of the homogeneous into the heterogeneous, and of the indefinite into the definite, it is also a transformation of the incoherent into the coherent. Along with the differentiation shown in increasing contrasts of parts with each other, there goes on an integration, by which the parts are rendered distinct units, as well as closely united components of one whole. These clauses here added to the definition, are essential ones; not only as being needful to distinguish Evolution from that which is not Evolution, but likewise as being needful to express all which the idea of Evolution includes. Progressive integration with the growing definiteness necessarily resulting from it, is of co-ordinate importance with the progressive differentiation before dwelt upon—nay, from one point of view, may be held of greater importance. For organization, in which what we call Evolution is most clearly and variously displayed, consists even more in the union of many parts into one whole, than in the formation of many parts. The Evolution which we see throughout inorganic nature, is lower than that which organic nature exhibits to us, for the especial reason that the mutual dependence of parts is extremely indefinite, even when traceable at all. In an amorphous mass of matter, you may act mechanically or chemically upon one part without appreciably affecting the other parts. Though their electrical or thermal states may be for the moment altered, their original states are soon resumed. Even in the highest inorganic aggregation—a crystal—the apex may be broken off and leave the rest intact: the only clear evidence of mutual dependence of parts, being, the ability of the crystal to regenerate its apex if replaced in the solution from which it was formed. But the constituent parts of organic bodies can severally maintain their existing states, only while remaining in connexion. Even in the lowest living forms, mutilation cannot be carried beyond a certain point without decomposition ensuing. As we advance through the higher up to the highest forms, we see a gradual narrowing of the limits within which the mutilation does not cause destruction: a progressive increase of mutual dependence or integration which is, at the same time, the condition to greater functional perfection. In societies this truth is equally manifest. That the component units slowly segregate into groups of different ranks and occupations, is a fact scarcely more conspicuous than is the fact that these groups are necessary to each other’s existence. And we cannot contemplate the still-progressing division of labour, without seeing that the interdependence becomes ever greater as the evolution becomes higher. It remains only to point out definitely, what has been already implied, that these several forms of change which have been successively described as making up the process of Evolution, are not in reality separate forms of change, but different aspects of the same change. Intrinsically the transformation is one and indivisible. The establishment of differences that become gradually more decided, is evidently but the beginning of an action which cannot be pushed to its extreme without producing definite divisions between the parts, and reducing each part to a separate mass. But with our limited faculties, it is not possible to take in the entire process at one view; nor have we any single terms by which the process can be described.