the (TwfjLa, or corporeal structure. We never find the organs of an aquatic animal with the ^vVis of a land animal. Everything relat- ing to the physiology of the animal is in harmony with its corpo- real organization. (2.) That where in all respects the physical nature of individuals or varieties is the same, there the species is the same ; Avhere the <^vcns is different, the species is different. (3.) That the physiology of an animal is thus as easily ascertained, and is just as uniform and fixed, as its material structure, and in fact much more so. The material structure may, and as we have seen does, differ exceedingly in the different varieties included under the same species, but the <^vo-ts is always the same. The physiology of the greyhound is identical with that of the mastiff; and that of the Shetland pony is the same as that of the Lon- don dray-horse.
Psychological Argument.
The third criterion of the identity of species is to be sought in the ^vxrj., or the psychological nature of the animal. The ^vx^ is the immaterial principle which belongs to all animals, and is the same in kind in every distinct species. It is that in v.-liich the life resides ; which is the seat of the instincts, and of that measure of intelligence, be it greater or less, which belongs to the animal. The ^vxr} is the same in all the individuals of the same species, and it is permanent. The instincts and habits of the bee, the wasp, the ant, and the beaver; of the lion, tiger, wolf, fox, horse, dog, and ox; and of all the endless diversities of beasts, birds, fishes, and insects, are the same in all ages and in all parts of the world. This im- material principle is of a higher order in some cases than in others, and admits of greater or less degrees of culture, as seen in the trained elephant or well-disciplined pointer. But the main thing is that each species has its own ^xQi ^^^ that this is a higher element and more decisive evidence of identity than the corporeal structure or even the <^vo-is, or animal nature. Where these three criteria concur, where the corporeal organization, in everything indicative of design, is the same ; where the <^vorts and the ^vxn, the physical and psychological natures, are the same, there, beyond all reasonable doubt, the species is the same.
The fourth criterion of species is found not only in its perma nence but in the capacity of procreation and indefinite propagation which belongs to all the individuals and varieties which it includes* Aninjals of the same species can propagate their kind. Animals of different species cannot combine and perpetuate a new or mongrel
86 PART n. Cu. IV. — UNITY OF THE HUMAN RACE.
species. This as we have seen is an admitted fact among all classes of naturalists, a few individuals excepted. It is a fact patent to all mankind and verified by the experience of all ages.
§ 3. Application of these Criteria to Man.
When we come to apply these several criteria to the human race, it is found beyond dispute that they all concur in proving that the whole human family are of one and the same species. In the first place the corporeal frame or external structui'e is the same in all the varieties of the race. There is the same num- ber of bones in the skeleton ; their arrangement and disposition are the same. There is the same distribution of the blood-vessels. The brain, the spinal marrow, and the nervous system are the same in all. They all have the same muscles amounting to many thousand in number. The organs for breathing, respiration, diges- tion, secretion, and assimilation, are the same in all. There are indeed indefinite diversities in size, complexion, and character, and colour of the hair, within the same variety of the race, and be- tween the varieties themselves. Some of these diversities are variable, and some are fixed. The Caucasian, the Mongolian, the African, have each their peculiarities by which the one is easily distinguished from the other, and which descend from generation to generation without alteration. With regard to these peculiari- ties, however, it is to be remarked, first, that they are less im- portant and less conspicuous than those which distinguish the different varieties of domestic animals all belonging to the same species. No two men, or no men of different races, differ from each other so much as the little Italian greyhound and the power- ful mastiff or bull-dog. And secondly, none of these peculiarities are indicative of difference of design, or plan, and therefore they are not indicative of difference in the immaterial principle, which according to the naturalists of the highest class, determines the identity of species and secures its permanence. And thirdly, these peculiarities are all referrible to the differences of climate, diet, and mode of life, and to the effect of propagation in case of acquired peculiarities. The truth of this last statement as to the influence of these several causes in modifying and perpetuating varieties in the same species, is abundantly illustrated and confirmed in the case of all the lower animals. Such is the sameness of all the varieties of mankind as to their corporeal structure, that a system of anatomy written in Europe and founded on the examination of the bodies of Europeans exclusively, would be as applicable in Asia, Africa, America, and Australia, as in Europe itself.