The second criterion of sameness of species is to be sought in the c^uo-is, or physical nature. In this respect also all mankind are found to agree, so that the physiology of the Caucasian, Mongo- lian, and African is precisely the same. The laws which regulate the vital processes are the same in all ; respiration, digestion, secre- tion, and propagation, are all conducted in the same way in every variety of the species.
The third criterion is found in the ij/vxn or psychological nature. This, as we have seen, is the highest test, for the i/'ux'? or imma- terial principle is the most important element in the constitution of every living creature. Where that is the same, the species is the same. There can be no reasonable doubt that the souls of all men are essentially the same. They not only have in common all the appetites, instincts, and passions, which belong to the souls of the lower animals, but they all share m those higher attributes which belong exclusively to man. They all are endowed with reason, conscience, and free agency. They all have the same constitu- tional principles and affections. They all stand in the same rela- tion to God as spirits possessing a moral and religious nature.
The fourth criterion is permanence, and the ability of indefinite propagation. We have seen that it is a law of nature, recognized by all naturalists (with a few recent exceptions), that animals of different species do not cohabit, and cannot propagate. Where the species are nearly allied, as the horse and the ass, they may pro- duce offspring combining the peculiarities of both pai*ents. But there the process stops. Mules cannot continue the mongrel race. It is however an admitted fact that men of every race, Caucasian, Mongolian, and African, can thus cohabit, and their offspring can be indefinitely propagated and combined. " Were these units [species]," says Professor Dana,^ "capable of blending with one another indefinitely, they would no longer be units, and species could not be recognized. The system of life would be a maze of complexities ; and whatever its grandeur to a being that could comprehend the infinite, it would be unintelligible chaos to man. ... It would be to man the temple of nature fused over its whole surface, and through its structure, without a line the mind could measure or comprehend." As therefore the universe is constructed on a definite plan ; as its laws are uniform ; and ns tlie con- stituent elements of the material world are permanent, it would be in strange contradiction with this universal analogy, if in the highest department of nature, in the organic and living world, 1 Biblioiheca Sacra, 1857, p. 863.
8S PAKT n. Ch. IV. — unity of the human eace.
everything should be unstable, so that species could mingle with species, and chaos take the place of order and uniformity. 'As therefore the different varieties of men freely unite and produce offspring permanently prolific, all those varieties must belong to one and the same species, or one of the most fixed of the laws of nature, is in their case reversed.
The Evidence of Identity of Race Cumulative.
It is to be observed that the strength of this argument for the unity of the human race does not depend upon any one of the above mentioned particulars separately. It is rather in their combina- tion that the power of the argument lies. It is not simply because the corporeal structure is essentially the same in all men ; nor simply because they have all the same physical, or the same psy- chological nature ; or that they are capable of producing perma- nently prolific offspring ; but because all these particulars are true in respect to the whole human family wherever found and through the whole course of its history. It becomes a mere matter of logomachy to dispute whether men are of the same species, if they have the same material organism, the same ^vo-ts and the same i/'uX^' Whether of the same species or not, if these things be admitted which cannot be rationally denied, they are of the same nature, they are beings of the same kind. Naturalists may give what meaning they please to the word species. This cannot alter the facts of the case. All men are of the same blood, of the same race, of the same order of creation.
"That the races of men, " says Delitzsch," are not species of one genus, but varieties of one species, is confirmed by the agreement in the psychological and pathological phenomena in them all, by similarity in the anatomical structure, in the fundamental powers and traits of the mind, in the limits to the duration of life, in the normal temperature of the body and the average rate of pulsation, in the duration of pregnancy, and in the unrestricted fruitfulness of marriages between the various races." ^
§ 4. Philological and Moral Evidence.
Besides the arguments above mentioned, which are all of a zoological character, there are others, not less conclusive, of a different kind. It is one of the infelicities which has attended this controversy, that it has been left too much in the hands of naturalists, of men trained to the consideration almost exclusivoij
1 Commentary on Genesis.