SECT. I.] HEREDITARY TRANSMISSION. 81 



It is a well known fact, that neither any two individuals nor 

 children of the same parents are perfectly like each other, but 

 that sometimes there exist considerable differences. Under 

 favourable circumstances these characteristic differences are 

 permanently transmitted to the offspring, whence may arise the 

 changes to which individuals of the same stock are subject, 

 which may contribute to an explanation of the differences ex- 

 isting in the physical organization of mankind. The differences 

 originating in this way become only permanently fixed, if 

 such individuals as possess them intermarry : cases which, in 

 modern civilized states of Europe, with its abundant popula- 

 tion and the separation of the various ranks of society, but 

 rarely occur, but which happened more frequently in primitive 

 states of society, when families lived in a comparatively isolated 

 state without much intercourse with foreign tribes. It has 

 been objected to this theory of the differences exhibited by the 

 races of mankind, that such spontaneous deviations from the 

 type of the primitive stock are not permanent, but disappear 

 again after a few generations (Morton). This objection, how- 

 ever, loses its importance on casting even a superficial glance 

 at our domestic animals, among whom it is shown that the 

 breed may be permanently improved. 



With regard to plants, it is now generally assumed that the 

 seed propagates the species only, but not always the variety. 

 In the animal world, deviations from the original type arise and 

 disappear more easily in some species than in others, and, 

 according to Prichard, 1 are more permanently transmitted, if 

 the deviations have arisen from pre-disposition rather than 

 from external circumstances. The breeding of domestic animals 

 is founded on the transmission of such spontaneous, and not 

 easily explicable, peculiarities, namely colour and quality of 

 skin and hair, tendency to become fat, strength, size and shape. 

 Even mental qualities are improved by the pairing of corres- 

 ponding individuals. 2 



The transmission of physical and mental qualities has been 



1 Loc. cit., i, p. 374. 



2 Many examples of this kind of individual peculiarities having become 

 hereditary, may be found in Heusinger, " Anthropol.," p. 93, and " Lucas, 

 Traite de 1'heredite," i, pp. 239, 291, 1847. 



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