998 OF THE BRANCHES OF THE HUMAN FAMILY. 



unity or diversity, is that furnished by the Generative process. It may be 

 considered as a fundamental fact, alike in the Vegetable and in the Animal 

 kingdom, that hybrid races originating in the sexual connection of individ- 

 uals of two different species, do not tend to self-perpetuation ; the hybrids 

 being nearly sterile with each other, although they may propagate with either 

 of their parent races, in which the hybrid race will soon merge ; whilst, on 

 the other hand, if the parents be themselves varieties of the same species, 

 the hybrid constitutes but another variety, and its powers of reproduction 

 are rather increased than diminished, so that it may continue to propagate 

 its own race, or may be used for the production of other varieties, almost ad 

 infinitwn. It appears that, among Plants, hybrids originating between un- 

 doubtedly distinct species, sometimes reproduce themselves for two or three 

 generations, but do not continue beyond the fourth. Amongst animals, the 

 limits of hybridity between parents of distinct species are more narrow, since 

 the hybrid is totally unable to continue its race with one of its own kind ; l 

 and although it may propagate with one of its parent-species, the progeny 

 will of course approach in character to the pure breed, and the race will 

 speedily merge into it. In Animals, as among Plants, the mixed offsprings 

 originating from different races within the limits of the same species gen- 

 erally exceed in vigor, and in the tendency to multiply, the parent-races from 

 which they are produced, so as to gain ground upon the older varieties, and 

 gradually to supersede them. In this manner, by the crossing of the breeds 

 of our domesticated animals, many new and superior varieties have been 

 produced. The general principle is, then, that beings of distinct species, or 

 descendants from stocks originally different, cannot produce a mixed race 

 which shall possess the capability of perpetuating itself; whilst the union of 

 varieties has a tendency to produce a race superior in energy and fertility to 

 its parents. The application of this principle to the Human races leaves no 

 doubt with respect to their specific unity ; for, as is well known, not only do 

 all the races of Men breed freely with each other, but the mixed race is 

 generally superior in physical development, and in tendency to rapid multi- 

 plication, to either of the parent stocks; so that there is much reason to 

 believe that, in many countries, the mixed race between the Aborigines and 

 European colonizers will ultimately become the dominant power in the com- 

 munity. This is especially the case in India, South America, and Polynesia. 

 844. The question of Psychical conformity or difference among the Races 

 of Mankind, is one which has a most direct bearing upon the question of 

 their specific unity or diversity ; but it has an importance of its own, even 

 greater than that which it derives from this source. For, as has been argued 

 with great justice and power, 2 the real Unity of Mankind does not lie in the 

 consanguinity of a common descent, but has its basis in the participation of 



one of the Negro tribes at an early age, and having spent two years among them, 

 seems to have been thoroughly acclimatized; and has subsequently passed many 

 years on the most unhealthy parts of tho coast, without experiencing any severe at- 

 tacks of illness, and in the enjoyment of very good general health. It is BomPtimes 

 maintained that the Negro race possesses such a complete exemption from the Yellow 

 Fever of the United States, as marks its specific difference; such, however, is not 

 constantly the case, since Negroes occasionally suffer from it; and their comparative 

 immunity seems fairly attributable to the constitutional peculiarity acquired by their 

 African progenitors, and capable of being acquired by Europeans also. 



1 One or two instances have been stated to occur in which a Mule has produced 

 offspring from union with a similar animal ; but this is certainly the extreme limit, 

 since no one has ever maintained that the race can be continued further than the 

 M-cnnd generation without admixture with one of the parent species. 



2 See the New Quarterly Review, No. xv, p. 131 ; and an Article by Prof. Agassiz 

 in the Christian Examiner, Boston (M. E ), 1850. 



