These diversities, so graphically described by Mr. Prichard, present a problem, the solution of which has occupied the most ingenious minds, especially of our times. The question of unity or plurality of the human species has of late excited much animated discussion; great names and weighty authorities are enlisted on either side, and a unanimous decision appears not likely to be soon agreed upon. But it is not my purpose, nor that of the author to whose writings these pages are introductory, to enter into a contest which to me seems rather a dispute about words than essentials. The distinguishing physical characteristics of what we term races of man are recognized by all parties, and whether these races are _distinct species_ or _permanent varieties_[2] only of the same, cannot affect the subject under investigation. In whatever manner the diversities among the various branches of the human family may have originated, whether they are primordial or were produced by external causes, their permanency is now generally admitted. "The Ethiopian cannot change his skin." If there are, or ever have been, external agencies that could change a white man into a negro, or _vice versa_, it is obvious that such causes have either ceased to operate, or operate only in a lapse of time so incommensurable as to be imponderable to our perceptions, for the races which now exist can be traced up to the dawn of history, and no well-authenticated instance of a transformation under any circumstances is on record. In human reasoning it is certainly legitimate to judge of the future by the experiences of the past, and we are, therefore, warranted to conclude that if races have preserved their identity for the last two thousand years, they will not lose it in the next two thousand. It is somewhat singular, however, that while most writers have ceased to explain the physical diversities of races by external causes, such as climate, food, etc., yet many still persist in maintaining the absolute equality of all in other respects, referring such differences in character as are undeniable, solely to circumstances, education, mode of life, etc. These writers consider all races as merely in different stages of development, and pretend that the lowest savage, or at least his offspring, may, by judicious training, and in course of time, be rendered equal to the civilized man. Before mentioning any facts in opposition to this doctrine, let us examine the reasoning upon which it is based.