From the evidence at hand it seems more than likely that many of the extant tribes have at some remote period been civilized, and that through some natural catastrophe, the unfavourable conditions of climate and soil, or some other equally disadvantageous cause, they have again sunk to a low plane of existence from which they have been unable to rise. From available facts one is almost led to believe that at a period in the remote past, and while living under purer conditions, a high stage of civilization was reached, a civilization which in many respects was equal if not superior to that of the present. Be this as it may, whenever the environment of a people is such that after having reached a certain stage it is unable to advance, it does not remain stationary, but on the contrary follows a line of retrogression; or, whenever the conditions of a race or tribe are such that the higher faculties which tend towards progress lie dormant, the lower forces which incline toward retrogression and which are peculiarly active in low organisms still continue in operation. Although the social arrangement of the native Australians seems to be founded on classes based on sex—the earliest form of society—still we find them practising polygamy and monogamy side by side, at the same time securing their wives by capture in exactly the same fashion as did the early Greeks and Romans. It is apparent, therefore, that although this people have not been able to advance in the arts of life, as far as the relations of the sexes are concerned they have taken about the same course as have all the other tribes and races in which the supremacy of the male has been gained. For unknown reasons, during thousands of years, the developing agencies have been quiescent, hence no check to the animal instincts has been interposed; the Australians have therefore departed widely from the conditions which surrounded early human society—conditions under which the maternal instincts developed in the lower orders of life were still sufficiently strong to guard the constructive processes and to continue the chain of uninterrupted progress.