Unless, therefore, we regard men as a solitary exception among all living beings, unless we withdraw them from the operation of the universal laws of nature, we must come to the conclusion that they do but form a certain number of races of one and the same species, and all descend from one primitive unique species.
Men are brothers in blood: this principle of universal fraternity imposed by nature, may be placed side by side with the corresponding maxim suggested by the moral sense.
Those who deny the unity of the human species, polygenists, or supporters of the plurality of human kind, base their arguments in favour of there being more than one species, upon the assertion that the distinction between the Negro and the white man is too great to permit of their possibly being classed together. But, between the lap-dog and the mastiff, the wild and tame rabbit, the spaniel and the greyhound, or the Shetland and Russian horse, there is a much greater difference than exists between the Negro and the white man. We are unable to state exactly, or to explain with any degree of accuracy, how it is that man, as he was first created, has given birth to races so widely different as the white, black, yellow, brown, and red which people the earth at the present day. We can but furnish a general explanation of what we see in the widely varying conditions of existence, and in the opposite character of the media through which man, for ages past, has dragged his existence, frequently with much difficulty and uncertainty. If the dog, the horse, the rabbit, and the turkey, through the agency of human industry applied to them during a period of scarcely two thousand years, have given birth to so many varieties, how much more would man, whose appearance upon the globe is of such antiquity that we cannot assign to it even approximatively a date—man, whose fate it has been to pass through so many different climates, such various physical and social positions, expect to see his own type become modified and transformed? We should, with more reason, feel surprised at finding that the differences between one variety and another are not much wider than they appear to be.
In order to avoid this argument, there remains to the supporters of the plurality of human kind no alternative but to regard man as an exception in nature; to assert that he has laws peculiar to himself, and that the principles which pervade the life of plants and animals can in no way apply to him. But man, who is an organized and living being, and is furnished with a body that differs but little from that of any mammiferous animal, is, so far as concerns his organization, subject to the universal laws of nature, and that of intermixture among the rest. It is therefore impossible to admit the question of exception raised by those who deny the unity of the human species.
The principle that the human species is one, and what follows as a natural conclusion, namely, that all men who inhabit the earth are but races or varieties of this one species, will, therefore, appear to the reader to be satisfactorily established.
These different races which originate in one species, the primitive type having been modified by the operation of climate, food, soil, intermixture and local customs, differ, it must be admitted, to a marvellous extent, in their outward appearance, colour and physiognomy. The differences are so great, the extremes so marked and the transitions so gradual, that it is well-nigh impossible to distribute the human species into really natural groups from a scientific point of view, that is to say, groups founded upon organic characteristics. The classification of the human races has always been the stumbling block of anthropology, and up to the present time the difficulty remains almost undiminished.
A cursory examination of the various classifications which have been brought forward by the most important of those who have essayed the task will make this truth apparent to all.
Buffon, in his chapter upon man; a work which we can always read again with admiration and advantage, contents himself with bringing forward the three fundamental types of the human species which have been known from the first under the names of the white, black and yellow race. But these three types in themselves do not exemplify every human physiognomy. The ancient inhabitants of America, commonly known as the Red-Skins, are entirely overlooked in this classification, and the distinction between the Negro and the white man cannot always be easily pointed out, for in Africa the Abyssinians, the Egyptians, and many others, in America the Californians, and in Asia the Hindoos, Malays and Javanese are neither white nor black.