But there is still a third realm, which is just as open to our observation as the history of the development of organisms and as geology, and of which we can also ask, whether it does not open for us an indirect way to the knowledge of the origin of species, and especially of man--a knowledge which we can no longer approach in the direct way of observation. This realm is _natural history_ and the _history of the development of the human race_. For mankind also is engaged in a process of development, and its present members do not stand on the same height. Now the question is, to what beginning can we trace backward the development of mankind, and to what succeeding stages of development from this present condition? And do we find in these earliest periods, and on these lowest stages, points that are connected with still earlier conditions and organizations, and especially points which could genealogically join together mankind and the animal kingdom? Three sciences, still young, favorite children of the present generation, participate in investigating this realm, namely, _archaeology_, _comparative ethnology_, and _comparative philology_. _Archaeology_ leads us back to far-off times. It is a fact that, chronologically speaking, man lived in the glacial period--according to French scientists, even before it; and that, palaeontologically speaking, man and {89} mammoth lived at the same time, and, according to a discovery made some thirty years ago at Denise in Middle France, probably even man and another older and defunct form of pachydermata, the elephas meridionalis, in North America man and the mastodon. The reader may compare the discoveries regarding the age of mankind, as they are described most recently by Sir Charles Lyell in his work upon this subject, in the publications of the Anthropological Congress at Brussels in the year 1873, and in those of the fourth General Assembly of the German Society for Anthropology, Ethnology and Primitive History, at Wiesbaden, in the year 1873.