The study of the human constitution not only denotes the real goal of our existence, but indicates to us what is meant by true culture and real progress. In earlier chapters, I have shown that philosophers have recognised the existence in man of a tendency to culture and progress. But what do they mean by these two words? Attempts have been made to define them as clearly as possible, and Herbert Spencer, the greatest of living philosophers, has devoted a special essay to the subject. He examined those phenomena that he regarded as progressive, first in the inorganic world, next, in the world of living things, and, finally, in humanity. He regards as progressive only the changes that tend to increase human happiness, and it is precisely on account of that tendency that he regards them as progressive. In order to define progressive phenomena Spencer thinks it necessary to make parallel studies of them in man and the animal world. He finds that progress is marked always by a transformation from the simple and uniform to the complex; and that it produces constant differentiation, in the evolution of the planetary world, in the embryonic development of the individual, and in the societies of men and animals. But differentiation is not a complete account of progress, for in the latter must be included the change of the indefinite into the definite. Spencer identifies progress with evolution, and his well-known definition of evolution is, that it is “an integration of matter and concomitant dissipation of motion; during which the matter passes from an indefinite, incoherent homogeneity to a definite, coherent heterogeneity; and during which the retained motion undergoes a parallel transformation.” Such a formula embraces too much, so that he is rather vague, especially when he applies it to human affairs. Differentiation in itself is not the whole of progress. It is necessary in each concrete case to inquire into its limits and modifications. The application of his theory of progress and evolution led Spencer, in his investigation of the basis of morality, to define human progress as the tendency towards a life as full and as long as possible. By fulness he means complexity, if I interpret his argument correctly. Civilised life as compared with savage life, is a realisation of progress. Civilised man, according to Spencer, uses food in a better regulated fashion, in accordance with the call and degree of his appetite; the food is of better quality, it is freed from contamination, is much more varied and is better prepared. The same differentiation distinguishes the clothing, the homes and so forth of civilised man. According to Spencer, all such progress helps real happiness, that is to say the fulness and the prolongation of life.