This hypothesis has been even elevated to a general thesis by several philologists, and M. d’Escayrac de Lauture, among others, believes that the centre of Africa, that land of the unknown and of mystery, is reserved to us as a spectacle of this phenomenon.[351] Without going back to origin, it is evident that two neighbouring peoples, in continual relation one with the other, ought to end by borrowing mutually the forms of language, letters, and articulation, especially when they have neither of them any literature capable of retaining the language within its limits, and of preserving it from all separation. Hence it results that anthropology must take its most precious authorities from the study of languages, in the language of the islands, for instance, and in the idioms spoken at the extremity of the continents: thus surrounded by the sea, in relation by its less extent with the others, these idioms will be preserved even more intact. We shall find here the real expression of the most ancient state of things which we can directly recognise by philology. The _click_ language, so peculiar to one single race,[352] exists only in the most southern part of Africa. They still speak the ancient Pali[353] in the south of Asia and at Ceylon. The most ancient language of Europe, so far as we know, namely the Celtic, still remains in Britanny and in Wales. From all which has gone before, we may then conclude that in order to establish a rational classification of human species, the first characteristics to be considered will be the _external aspect_, and perhaps the _moral characteristics_; the rest will come in the second rank: at first, language, then deep anatomical varieties which do not strike us at the first glance, then physiological and pathological varieties, etc. Such is, we think, the only certain basis upon which anthropology can rest--the true distinctions between human species. We do not even yet know exactly their number, and naturalists do not at all agree on this subject; the work is to be done over again, by following a new route.