And now the question arises, How are these varieties to be regarded in the light of science? Are they aboriginal and from the beginning,--or are they super-induced by secondary causes, of which the record is lost in the extended night preceding our historic day? Here the authorities are divided. On the one side, we are reminded that within the period of recognized chronology no perceptible change has occurred in any of these varieties,--that on the earliest monuments of Egypt the African is pictured precisely as we see him now, even to that servitude from which among us he is happily released,--and it is insisted that no known influences of climate or place are sufficient to explain such transformations from an aboriginal type, while plural types are in conformity with the analogies of the animal and vegetable world. On the other side, we are reminded, that, whatever may be the difficulties from supposing a common centre of Creation, there are greater still in supposing plural centres,--that it is easier to understand one creation than many,[133]--that geographical science makes us acquainted with intermediate gradations of color and conformation in which the great contrasts disappear,--that, even within the last half-century and in Europe, people have tended to lose their national physiognomy and run into a common type, thus attesting subjection to transforming influences,--that, after accepting the races already described, there are other varieties, national, family, and individual, not less difficult of explanation,--and it is insisted, that, whatever these varieties, be they few or many, there is among them all _an overruling Unity_, by which they are constituted one and the same cosmopolitan species, endowed with speech, reason, conscience, and the hope of immortality, knitting all together in a common Humanity, and, amidst all seeming differences, making all as near to each other as they are far apart from every other created thing, while to every one is given that great first instrument of civilization, the human hand, by which the earth is tilled, cities built, history written, and the stars measured;--and this unquestionable Unity is pronounced all-sufficient evidence of a common origin.