We have now arrived at the limits of the task which we proposed to attempt, and we hope, after what has gone before, that we shall be able to arrive at some scientific conclusion. After having endeavoured to establish in the introduction the route we had to follow in anthropological studies, we gave an account of the system of purely philosophic researches, putting every foreign or prejudicial idea on one side, and, resting on facts and on mathematical reasoning, we have endeavoured to apply these principles. We endeavoured at first to prove that man was not a being as foreign and superior to the rest of animal nature, as certain naturalists have thought, taking themselves, the first from among men, as the point of comparison. We have considered the inferior races, and we have shown that between these and the first animals the distance was neither absolute nor well-defined; that man came into the zoological series, and that he only forms definitively a separate _family_. Changing our direction, we abandoned this acquired knowledge, and we passed on to the study of varieties among men; we found them profound, indeed, and of every description. Then came the study of the influences to which man may be subjected. We saw that hybridity did not play any serious part in this, since it could only weaken pre-existing differences. On the other hand, we have acknowledged that _in the limits of time accessible to our knowledge_, nothing justified the hypothesis, that climate had such an extensive influence in changing man so as to make the differences which we may observe between ancestors and descendants such as would suffice, in any other zoological group, to characterise distinct species. In regarding man as a separate kingdom, we are, by this fact, exempted from applying the same rules as in zoology; but, by proving that he comes into the zoological series, we have implicitly proved that he must be submitted to the same laws. Science cannot have two different modes of proceeding: it must follow the same paths in the same subjects in order to arrive at comparable results. It is the only truly philosophic road: nature is _one_, and the work of the modern sciences is precisely to tend towards unity. The most diverse phenomena in the hands of analysts compare and assimilate themselves to the rays of a spirit of synthesis; magnetism, electricity, light, heat, motion, everything is mingled and linked together so well, that we know not how to make a distinction any more. The pure and simple adoption of the law of organic unity brings us to the following proposition:-- PROPOSITION.--_Either we must admit different species in the genus Homo, or we must entirely reform zoological classification._