CONCLUDIXG KEMARKS. 227. 



naturalist relies for the determination of the genus and 

 species of the orangs and chimpanzees, have such an 

 origin or dependent relation. The great superorbital 

 ridge, e. g. against which the facial line rests in Fig. 50, 

 is not the consequence of muscular action or develop- 

 ment : it is characteristic of the genus Troglodytes from 

 the time of birth ; and we have no grounds for believing 

 it to be a character to be gained or lost through the ope- 

 rations of external causes, inducing particular habits 

 through successive generations of a species. 



No known cause of change productive of varieties of 

 mammalian species could operate in altering the size, 

 shape, or connections of the prominent premaxillary 

 bones, which so remarkably distinguish the great Troglo- 

 dytes gorilla from the lowest races of mankind. There is 

 not, in fact, any other character than that founded upon 

 the development of bone for the attachment of muscles, 

 which is known to be subject to change through the 

 operation and influence of external causes. Nine-tenths 

 of the differences which have been cited (see the Transac- 

 tions of the Zoological Society^ vol. iii. p. 413), as distin- 

 guishing the great chimpanzee from the human species, 

 must stand in contravention of the hypothesis of trans- 

 mutation and progressive development, until the acceptors 

 of that hypothesis are enabled to adduce the facts demon- 

 strative of the conditions of the modifiability of such 

 characters. Moreover, as the generic forms of the ape 

 tribe approach the human, type, they are represented by 

 fewer species. The unity of the human species is demon- 

 strated by the constancy of those osteological and dental 

 peculiarities which are seen to be most characteristic of 

 the himana in contradistinction from the qiiadrumana. 



Man is the sole species of his genus (homo) — the sole 



