OF THE HUMAN SPKCIES. 471 



lectual qualities, which characterize the several races of our 

 species, are analogous in kind and degree to those which 

 distinguish the breeds of the domestic animals ; and must, 

 therefore, be accounted for on the same principles, 2dly, 

 That they are first produced, in both instances, as native or 

 congenital varieties ; and then transmitted to the offspring 

 in hereditary succession. 3dly, That of the circumstances 

 which favour this disposition to the production of varieties 

 in the animal kingdom, the most powerful is the state of do- 

 mestication. 4thly, That external or adventitious causes, 

 such as climate, situation, food, way of life, have consider- 

 able effect in altering the constitution of man and animals ; 

 but that this effect, as well as that of art or accident, is con- 

 fined to the individual, not being transmitted by generation, 

 and therefore not affecting the race. 5thly, That the human 

 species, therefore, like that of the cow, sheep, horse, and 

 pig, and others, is single; and that all the differences, 

 which it exhibits, are to be regarded merely as varieties. 



If, in investigating the subject, we are satisfied with com- 

 paring the existing races of men to those of the domestic 

 animals, and with bringing together the characteristic marks, 

 on which the distinctions are grounded in the two cases, as 

 1 have done in several preceding chapters, we shall have no 

 difficulty in arriving at the fifth conclusion. If, however, 

 we should carry ourselves back, in imagination, to a sup- 

 posed period, when mankind consisted of one race only — 

 and endeavour to shew how the numerous varieties, which 

 now occupy the different parts of the earth, have arisen out 

 of the common stock, and have become so distinct from 

 each other, as we find them at present — we cannot arrive at 

 so satisfactory a decision ; and we experience further embar- 

 rassment from the fact, that the races have been as distinctly 

 marked, and as completely separated from the earliest 

 periods, to which historical evidence ascends, as they now 

 are. The same remarks, in great measure, are true, con- 

 cerning animals ; so that, on this ground, no difficulty pre- 

 vents us from recognizing the unity of the human species, 

 which is not equally applicable to them. 



