16 EVOLUTION while an invention like that of the steam en- gine works its multiform effects throughout civilization. By this law the principle of the instability of the homogeneous is powerfully reenforced, and the cause of universal move- ment toward greater diversity is rationally ex- plained. But these modes of action alone could only result in a vague chaotic hetero- geneity, and could not account for that orderly heterogeneity in which evolution essentially consists. 4. This finds explanation in the principle of segregation. When a mass is acted upon by forces which promote the re- distribution of its parts, its units are not only differentiated and regrouped, but there is a se- gregation of like units which become separated from the neighboring groups. A familiar ex- ample of this is seen in the winnowing pro- cess, by which a force applied to a mixed mass brings all the grain together in one place and the chaff in another. The same thing is seen when several salts are dissolved in a liquid, and each crystallizes out by the combi- nation of like chemical molecules. The or- ganism conforms to this principle from its ear- liest stage of growth, the special elements of the bony, muscular, and nervous systems being withdrawn from the nourishing fluids and se- gregated in the distinctive parts. We have already seen that natural selection is a win- nowing process, by which the unfit are ex- cluded, and the better adapted are separated and preserved. In social development the same thing is seen. Not only are there con- tinual differentiations of groups and classes by which society becomes heterogeneous, but these groups are unified by similarity of oc- cupation, character, taste, and race. Stock brokers cluster in Wall street,, and the Mor- mons segregate in Utah. Thus in all the spheres of change redistribution leads to unification. 5. This end is farther promoted by the important dynamical law that mo- tion takes' place along lines of least resis- tance. The operation of this principle in in- organic nature is self-evident. Water forms its channels in the direction of least obstacles. Mr. James Hinton has shown that organic growth takes place in obedience to this law, and Mr. Spencer proves that it governs both mental and social changes. This law, in con- nection with the principle that movement set up in any direction is a cause of further move- ment in that direction, by which lines of con- nection become established, goes far to account for that integration of structures and functions which is disclosed in all phases of evolution. But can evolution go on for ever, or is it lim- ited ? This brings us to the process by which it is constantly antagonized and always finally terminated, the counter-agency of dissolution. All redistributions of matter and motion are either evolution or dissolution, but neither of these processes ever goes on absolutely unquali- fied by the other, and the change in either di- rection is but a differential result of the con- flict. Mr. Spencer's formula, to be complete, must embrace both sets of correlative changes, and its determination led him to the following universal law : 6. Every change wrought in an object must be either a transposition of its mass, or a variation of its internal or molecu- lar motion. As it loses this contained or in- sensible motion, there follows a concentration of the parts and increasing integration ; if it acquires insensible motion, there is dispersion of the particles, or disintegration ; that is, with concentration of matter there is dispersion of motion, and with absorption of motion there is diffusion of matter. These are the two as- pects of the universal metamorphosis, and when approximately balanced there is equilibration., Evolution is integration ; dissolution is disin- tegration. We have here confined ourselves to the most abstract statement of Mr. Spen- cer's theory ; its concrete applications will be found extensively worked out in his "First Principles" and in the biological, psycholo- gical, and sociological divisions of his Philo- sophical System." As a method of philoso- phy it aims only to explain phenomena; all phenomena being regarded as manifestations of the unknown power which transcends the reach of thought. Philosophy is regarded as the highest explanation of things, and as each science is unified by its largest induc- tions, the family of sciences is brought into a completer unity by a law that comprehends them all. Whatever ultimate form the the- ory of evolution may take, its influence must be powerfully felt in the direction of future inquiries; for many who withhold their assent from it as an established truth of nature never- theless recognize it as an invaluable working hypothesis. As remarked by Prof. Grove: " The first question is, does the newly proposed view remove more difficulties, require fewer assumptions, and present more consistency with observed facts than that which it seeks to supersede ? If so, the philosopher will adopt it, and the world will follow the philosopher, after many days." Mr. Spencer's theory has been clearly summed up by himself in the fol- lowing propositions: "1. Throughout the uni- verse, in general and in detail, there is an un- ceasing redistribution of matter and motion. 2. This redistribution constitutes evolution where there is a predominant integration of matter and dissipation of motion, and consti- stutes dissolution where there is a predominant absorption of motion and disintegration of mat- ter. 3. Evolution is simple when the process of integration, or the formation of a coherent aggregate, proceeds uncomplicated by other processes. 4. Evolution is compound when, along with this primary change from an inco- herent to a coherent state, there go on secon- dary changes due to differences in the circum- stances of the different parts of the aggregate. 5. These secondary changes constitute a trans- formation of the homogeneous into the hetero- geneous a transformation which, like the first,
