From the present condition and past his tory of the domesticated races of Mammalia, of which a general survey has thus been taken, some important inferences may be drawn, which it may be advisable to put in the shape of formal propositions ; since in this manner we shall be able to define our terms more strictly, and to use these definitions as the foundation for our future investigations into the relationship of the several branches of the Human family.
1. Races of living beings are, properly, successions of individuals propagated from any given stock ; and the term implies no more than the fact of the transmission of a distinctive character by descent.
2. Two races, distinguished by well-marked peculiarities, may rank either as distinct spe cies, or as varieties of the same species ; being supposed, in the first case, to be descended from parents which themselves originally ex hibited the same peculiarities ; and being considered, in the second, as the descendants of an identical, or, at any rate, of a similar, parentage.
3. The question of unity or diversity of species, between two races, cannot be decided by the degree of difference which exists be tween them ; for the answer to it entirely depends upon the constancy with which the peculiarity (of whatever nature it may be) is transmitted from parent to offspring, and upon the amount of variation which is exhibited even within the acknowledged limits of the respective races. And thus a character which is perfectly valid in one group, may be en tirely inapplicable in another.
4. Two races can only be regarded ' as specifically distinct, when the characters which separate them are transmitted with complete uniformity from parent to offspring ; when there are no intermediate gradations tending to connect them ; and when no such tendency to variation has manifested itself in either race, as shall make it probable, or, at any rate, possible, that their differences may be the direct result of external influences, or may be attributed to an unusual divergence in the characters of the offspring from those of the parents. • .5. On the other hand, two races may un doubtedly be regarded as specifically identical, when, however great the differences in stature, conformation, psychical character, &c., pre sented by their respective types, ;hese types are connected with each other by inter mediate gradations, so close as to render it impossible to establish a definite boundary line between the collections of individuals which are assembled around them.
6. Again, two races may be undoubtedly regarded as specifically identical, when in either race varieties present themselves, which ex hibit the distinctive characters of the other race ; since we then have evidence, that, al though these peculiarities are so generally transmitted from parent to offspring that each race possesses a certain degree of permanence, yet they are not thus uniformly inherited ; and, consequently, there is nothing to pre vent the transformation of the one race into the other, if the circumstances which have originated the variation, even in a single case, should act with sufficient potency on the whole mass.
7. No character can be safely adopted as assumption of the specific di- versity of two races, which has been found by experience to undergo considerable modifica tion in either race, even though such mo dification should not proceed to the extent of conversion into the character of the other ; for if a limited amount of change in external conditions be found capable of effecting a certain degree of alteration, the probability is strong that the higher difference may have had its origin in the more potent operation of the same class of causes.
8. The very fact of the extensive dispersion of a race, and of its existence under a great variety of external conditions, implies a marked capacity for variation ; since without such capacity, the race could not continue to flourish.
9. Among the conditions which most tend thus to produce varieties, within the limits of species, are those that are included under the general term domestication ; and the widest . divergence among these varieties is to be found in those species, which are brought into the closest relation to Man.
Among the domesticated races of quad rupeds, the characters most of variation are,— L Stature ; — 2. General con formation of the body, as dependent upon the proportionate development of the limbs and trunk, the proportion of the breadth and thickness of bones to their length, the relative development of the soft tissues in different parts, &c. &c. ;-3. Conformation of the skull, as shown especially in the relative development of the cranial and facial portions, the capacity of the cranial cavity, and the elongation of the muzzle ; — 4. Quantity, texture, and colour of the hairy covering ; — 5. Psychical character, as shown in the increase of intelligence, in the acquirement of new methods of action, and in the disappearance of some of the na tural instinctive propensities.