Chap. IV.] MANNER OF DEVELOPMENT. 139 



nants, apparently in relation with the development of 

 their horns ; and in horses, in relation with their habit of 

 fighting with their incisor teeth and hoofs. 



In the adult male anthropomorphous apes, as Riiti- 

 meyer, 68 and others have insisted, it is precisely the effect 

 which the jaw-muscles by their great development have 

 produced on the skull, that causes it to differ so greatly in 

 many respects from that of man, and has given to it " a 

 truly frightful physiognomy." Therefore, as the jaws and 

 teeth in the progenitors of man gradually become reduced 

 in size, the adult skull would have presented nearly the 

 same characters which it offers in the young of the an- 

 thropomorphous apes, and would thus have come to 

 resemble more nearly that of existing man. A great re- 

 duction of the canine teeth in the males would almost cer- 

 tainly, as we shall hereafter see, have affected through 

 inheritance the teeth of the females. 



As the various mental faculties have gradually de- 

 veloped, the brain would almost certainly have become 

 larger. !N"o one, I presume, doubts that the large size of 

 the brain in man, relatively to his body, in comparison to 

 that of the gorilla or orang, is closely connected with his 

 higher mental powers. We meet with closely-analogous 

 facts with insects, in which the cerebral ganglia are of 

 extraordinary dimensions in ants ; these ganglia in all the 

 Hymenoptera being many times larger than in the less in- 

 telligent orders^ such as beetles. 69 On the other hand, no 

 one supposes that the intellect of any two animals, or of 

 any two men, can be accurately gauged by the cubic con- 



68 ' Die Grenzen der Thierwelt, eine Betrachtung zu Darwin's Lehre,' 

 1868, s. 51. 



69 Dujardin, ■ Annates des Sc. Nat.' 3d series, Zoolog. torn. xiv. 1850, 

 p. 203. See also Mr. Lowrie, ' Anatomy and Phys. of the Musca vomito. 

 via,' 18*70, p. 14. My son, Mr. F. Darwin, dissected for me the cerebral 

 ganglia of the Formica rufa. 



