December, 1927 



EVOLUTION 



Pace Three 



Gorilla Bab\/ 



The Testimony of Man's Teeth 



By William K. Gregory 



"THE infant gorilla that is now in the Philadelphia Zoo- 

 logical Park is a friendly little chap, wanting chiefly 

 to be babied and fussed with. So it is not surprising 

 that he let me put my finger in hie mouth to feel his 

 teeth. If he lives several years longer he should, if he 

 is like other young gorillas, eventually have a full set 

 of milk teeth numbering twenty in all and arranged as 

 follows: 



on either side of the upper jaw 

 two incisors, one canine, two "milk molars"; 



on either side of the lower jaw 



two incisors, one canine, two "milk molars." 



Is it a mere coincidence that normal human children 



also have twenty milk teeth? And that they also have, 



on either side of the upper jaw 



two incisors, one canine, two "milk molars"; 



and on either side of the lower jaw 

 two incisors, one canine, two "milk molars"? 

 And is it a further coincidence that when gorilla and 

 human children grow up they should as a rule have 

 thirty-two teeth in the adult set, arranged as follows: 



on either side of the upper jaw 

 two incigors, one canine, two premolars, three molars; 



and on either side of the lower jaw 

 two incisors, one canine, two premolars, three molars? 



And is it not significant that these particular numbers 

 and arrangements of the milk and adult teeth in all 

 the class of mammals are found only in the higher or 

 Old World monkeys, apes and man? Is man made 

 literally in the image of God in this respect also? Or 

 did he inherit his normal "dental formula" from some 

 far-off members of the ancestral stock of the anthropoid 

 apes, as Darwin inferred? 



Let us follow this line further. How many principal 

 points or cusps has the reader got on his second right 

 or left lower molar? If he is like most people he will 

 find only four cusps, separated from each other at their 

 bases by two main grooves forming a cross. This is a 

 distinctly human arrangement and taken by itself is a 

 conspicuous point of difference from the corresponding 

 tooth of all the known apes, living and fossil, which have 

 normally five cusps on the second lower molar. 



But about one-fourth of white people have a fifth cusp 

 on the first lower molar and a good many negroes, black 

 Australians and other primitive individuals have five 

 cusps on all three lower molars. And as there are 

 hundreds of jaws in which the fifth or hinder cusp has 

 almost disappeared, so there are other jaws in which 

 it is less and less reduced. In the most ancient fossil 

 human jaws known, namely the Heidelberg jaw, the 



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twoffiilXmolars 

 lower 



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