A host of manifestations of human activity are derived, as so many consequences, from the three facts which I have pointed out. Customs and institutions of every kind are connected with them; they alone explain some of the great events which change the destiny of nations and the face of the earth. For reasons which I have several times pointed out already, we must give a name to the _Unknown Cause_ from which are derived the phenomena of morality and religion. We will call it the _Human mind_ (l’âme humaine). I must here repeat the formal declaration which I have often made already. When I employ this term, which is established by custom, it is with the understanding that I strictly confine myself within the limits imposed upon anyone who intends to be exclusively faithful to science, experiment and observation. I consider the human principle as the _Unknown Cause_ of exclusively human phenomena. To go beyond that would be to encroach upon the domain of philosophy or theology. To them belongs the solution of the formidable problems raised by the existence of the ‘_something_’ which makes a man of an organism entirely animal, and I give everyone leave to choose from the proposed solutions the one which agrees most satisfactorily with the demands of his own feelings and reason. But whatever this solution may be, it will in no way affect the phenomena; those which I have just described will neither be diminished nor modified. Now they exist in man alone, and it is impossible to deny their importance. Thus they distinguish man from the animal as much as the phenomena of intelligence distinguish the animal from the plant, and as the phenomena of life distinguish the plant from the mineral. They are, therefore, the attributes of a kingdom, which we will call the _Human Kingdom_. From this conclusion it will seem that I am at variance with Linnæus, whose idea I have, however, only developed and stated more precisely. In fact, the immortal author of the _Systema Naturæ_ has placed his _Homo sapiens_ amongst the mammalia in the class of primates, and has made him congenous with the gibbon. This is because Linnæus had recourse to the _System_ in order to establish his _nomenclature_. To classify man as well as other beings, he has made an arbitrary choice of a certain number of characteristics, and only taken those into consideration which were furnished by the body. But the language of Linnæus is very different, even in his remarks relating to the genus _Homo_, and still more so in the kind of introduction entitled _Imperium Naturæ_. He there almost places man in opposition with all beings, and particularly with animals, and in such terms as necessarily to suggest the idea of a _human kingdom_.