Many pages would be requisite adequately to describe the result of the inquiries prosecuted by Mr. Spencer during some twenty years, and embodied in the three volumes entitled “Principles of Sociology.”  The ultimate conclusions reached, however, may be summed up in a few paragraphs.  It is the author’s final conviction that, if the process of evolution, which, unceasing throughout past time, has brought life to its present height, continues throughout the future, as we cannot but anticipate, then, amid all the rhythmical changes in each society, amid all the lives and deaths of nations, amid all the supplantings of race by race, there will go on that adaptation of human nature to the social state which began when savages first gathered together into hordes for mutual defence,—­an adaptation finally complete.  Mr. Spencer foresees that many will think this a wild imagination.  Though everywhere around them are creatures with structures and instincts which have been gradually so moulded as to subserve their own welfares and the welfares of their species, yet the immense majority ignore the implication that human beings, too, have been undergoing in the past, and will undergo in the future, progressive adjustments to the lives imposed on them by circumstances.  There are a few, nevertheless, who think it rational to conclude that what has happened with all lower forms must happen with the highest forms,—­a few who infer that among types of men those most fitted for making a well-working society will hereafter, as heretofore, from time to time, emerge and spread at the expense of types less fitted, until a fully fitted type has arisen.

It is, at the same time, conceded that the view thus suggested cannot be accepted without qualification.  If we carry our thoughts as far forward as palaeolithic implements carry them back, we are introduced, not to an absolute optimism, but to a relative optimism.  The cosmic process brings about retrogression, as well as progression, where the conditions favor it.  Only amid an infinity of modifications, adjusted to an infinity of changes of circumstances, do there now and then occur some which constitute an advance:  other changes, meanwhile, caused in other organisms, usually not constituting forward steps in organization, and often constituting steps backward.  Evolution does not imply a latent tendency to improve everywhere in operation.  There is no uniform ascent from lower to higher, but only an occasional production of a form, which, in virtue of greater fitness for more complex conditions, becomes capable of a longer life of a more varied kind.  And, while such higher type begins to dominate over lower types, and to spread at their expense, the lower types survive in habitats or modes of life that are not usurped, or are thrust into inferior habitats or modes of life in which they retrogress.