j 4 m The Descent of Man. Fart 1. 



In the adult male anthropomorphous apes, as Biitimeyer, 77 

 and others, have insisted, it is the effect on the skull of the great 

 development of the jaw-muscles that causes it to differ so greatly 

 in many respects from that of man, and has given to these 

 animals " a truly frightful physiognomy." Therefore, as the jaw s 

 and teeth in man's progenitors gradually became reduced in size, 

 the adult skull would have come to resemble more and more 

 that of existing man. As we shall hereafter see, a great reduction 

 of the canine teeth in the males would almost certainly affect the 

 teeth of the females through inheritance. 



As the various mental faculties gradually developed themselves 

 the brain would almost certainly become larger. No one, I 

 presume, doubts that the large proportion which the size of 

 man's brain bears to his body, compared to the same proportion 

 in the gorilla or orang, is closely connected with his higher 

 mental powers. We meet with closely analogous facts with 

 insects, for in ants the cerebral ganglia are of extraordinary 

 dimensions, and in all the Hymenoptera these ganglia are many 

 times larger than in the less intelligent orders, such as beetles. 78 

 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 contents of their skulls. It is certain that there may be 

 extraordinary mental activity with an extremely small absolute 

 mass of nervous matter : thus the wonderfully diversified 

 instincts, mental powers, and affections of ants are notorious 

 yet their cerebral ganglia are not so large as the quarter of a 

 small pin's head. Under this point of view, the brain of an ant is 

 one of the most marvellous atoms of matter in the world, perhaps 

 more so than the brain of a man. 



The belief that there exists in man some close relation between 

 the size of the brain and the development of the intellectual 

 faculties is supported by the comparison of the skulls of savage 

 and civilised races, of ancient and modern people, and by the 

 analogy of the whole vertebrate series. Dr. J. Barnard Davis has 

 proved, 79 by many careful measurements, that the mean internal 

 capacity of the skull in Europeans is 92*3 cubic inches ; in 

 Americans 87*5 ; in Asiatics 87"1 ; and in Australians only 81*9 

 eubio inches. Professor Broca 80 found that the nineteenth centurv 



%f 



: " ' Die Grenzen der Thierwelt, vomitoria* 1870, p. 14. My son, 



ttne Betrachtung zu Darwin's Lehre,' Mr. F. Darwin, dissected for me the 



1868, s. 51. cerebral ganglia of the Furmicn 



78 Du jardin, ' Annales des Sc. rufa. 



Nat,' 3rd series Zoolog. torn, xiw 79 < Philosophical Transactions, 



1850, p. 203. See also Mr. Lowne. 1809, p. 5L3. 



'Anatcmy and Phys. of the Mu<:a 6 " ' Les Selections,' M. P. Broca, 



