Opinions of Naturalists and Philosophers

At least, this has been hitherto the view which naturalists and philosophers have almost unanimously taken of this subject, though there have not been wanting writers who have maintained the contrary opinion. Notwithstanding the evidence furnished by the appearance of fossil remains, that the lines of demarcation separating the different species are absolutely and forever impassable, there have been some advocates of the theory that all the present races of animals may have been derived by insensible gradations from a few primordial types. This theory has very recently been brought forward anew in a form to attract general attention. Still, so unanimous and so decisive has been the testimony of geologists in respect to the evidence furnished by the fossil remains, and so inconsistent is it with the development theory, as it is called, that very great changes must take place in the opinion of naturalists in respect to the true import of the geological records before this opinion can be generally received.

But however the great question in respect to the absolute and perpetual permanence of the distinction of species may be ultimately decided, there is no doubt that all naturalists fully concur in the opinion that this permanence is, at all events, so great as entirely to preclude the possibility that the American species of plants and animals can have descended from the stocks of the old world within so short a period as six thousand years. Some other supposition must, therefore, be made than that the forms of life existing here could have been derived, within that period, by ordinary generation from those prevailing in other portions of the world. Some of the principal suppositions which have been made will be presently alluded to.