"We believe we have shown beyond question that that which the German physiologists (Von Baer, Wolff, and others) have found to be the law of organic development (as of a seed into a tree, and of an egg into an animal), is the law of all development. The advance from the simple to the complex, through a process of successive differentiations (i. e., the appearance of differences in the parts of a seemingly like substance), is seen alike in the earliest changes of the Universe to which we can reason our way back; and in the earlier changes which we can inductively establish; it is seen in the geologic and climatic evolution of the Earth, and of every single organism on its surface; it is seen in the evolution of Humanity, whether contemplated in the civilised individual, or in the aggregation of races; it is seen in the evolution of Society in respect alike of its political, its religious, and its economical organisation; and it is seen in the evolution of all those endless concrete and abstract products of human activity which constitute the environment of our daily life. From the remotest past which Science can fathom, up to the novelties of yesterday, that in which Progress essentially consists, is the transformation of the homogeneous into the heterogeneous" (Essays, vol. i, 1883, p. 30). To this may fitly follow the "succinct statement of the cardinal principles developed in the successive works," which Mr. Spencer, as named above, prepared for Professor Youmans. 1. Throughout the universe in general and in detail there is an unceasing redistribution of matter and motion. 2. This redistribution constitutes evolution when there is a predominant integration of matter and dissipation of motion, and constitutes dissolution when there is a predominant absorption of motion and disintegration of matter. 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 incoherent to a coherent state, there go on secondary changes due to differences in the circumstances of the different parts of the aggregate. 5. These secondary changes constitute a transformation of the homogeneous into the heterogeneous--a transformation which, like the first, is exhibited in the universe as a whole and in all (or nearly all) its details; in the aggregate of stars and nebulæ; in the planetary system; in the earth as an inorganic mass; in each organism, vegetal or animal (Von Baer's law otherwise expressed); in the aggregate of organisms throughout geologic time; in the mind; in society; in all products of social activity.