SECT. IV.] RESULTS. 229 



all the peoples of the earth were true mongrels, a second 

 one : that all these mixed types possess a persistent vitality 

 without any infusion of fresh blood from the stock they have 

 sprung from ; and further, that their own types are pre- 

 served without any reversion to that of the parent stock, by 

 which the assumed specific differences are neutralized and ren- 

 dered illusory. 



It is unquestionable that, among the causes which induce 

 permanent changes of type, intermixture is the most potent, 

 and that in comparison with this agent other influences seem 

 less important. Though this circumstance renders the suppo- 

 sition of several originally different races in some degree pro- 

 bable, it still remains, in by far the greater number of cases, 

 impossible to determine whether an intermixture of different 

 elements has taken place at all, and how far it has progressed. 

 Intermixture, moreover, as we have seen, is not the sole agent. 

 We can, therefore, scarcely go further than this, that every- 

 where, and especially when in an uncivilized state, a number 

 of human beings, possessing the same habits and modes of 

 life, will, by continued intermixture of the individuals between 

 themselves through a series of generations, if they live in a 

 state of seclusion, acquire in the course of time a nearly uni- 

 form external type, whatever may have been the original 

 elements. 



The whole result of the preceding investigation may there- 

 fore be summed up to this effect : that the known facts not 

 only permit the assumption of the unity of the human species, 

 but that this view presents less difficulties than the opposite 

 theory of specific differences ; because any number of species 

 assumed, appears equally arbitrary. But as the principal argu- 

 ments in favour of unity of species rest upon the mutability of 

 the human organism by internal and external influences, the 

 limits of which are unknown to us ; and as in the absence of 

 any exact information as to the length of time they were 

 in action, we cannot decide whether the power of these influ- 

 ences was sufficient to produce the existing differences, the 

 question of unity of species remains an open one. Even 

 if it were satisfactorily proved that the magnitude of the 



