MISSING TEETH INHERITED 



Lateral Incisors and Third Molars or "Wisdom Teeth" Most Frequently Absent- 

 Cause to be Sought in Evolution of Man and Change of His Habits 

 of Eating — Loss of Importance of Canine Teeth. 



Dr. Sergio Sergi 

 Institute of Anthropology, Royal University of Rome, Italy} 



1HAVE made the acquaintance of an 

 educated Piedmontese youth who 

 shows the congenital absence of the 

 upper lateral right incisor; he has 

 informed me that his father, his two 

 brothers and their two sisters, all older 

 than he, present the same defect, as 

 did an uncle, his father's only brother; 

 and his paternal grandfather. In all of 

 them, the absence of the tooth is accom- 

 panied by a noticeable reduction in 

 size of the corresponding incisor on the 

 left side. 



Dental agenesia as a phenomenon 

 of heredity has been noted by a number 

 of observers in the past. Hereditary 

 absence of the lateral incisors has been 

 observed in two or three generations 

 and the inheritance may be either 

 direct or alternate. Magitot refers to a 

 woman who showed a lack of the upper, 

 lateral incisors, as did her daughter and 

 nephew; and of a man who lacked the 

 lateral upper right incisor, as did his 

 daughter and his nephew; Leroy d'Eti- 

 olle describes the same sort of agenesia 

 in a woman and her three sons. 



Perrin has cited the case of a family 

 in various members of which the two 

 upper lateral incisors were lacking, and 

 says the defect had existed in the family 

 for many generations. 



The phenomenon of congenital ab- 

 sence of teeth, like that of the augmenta- 

 tion of their number, is a form of 

 meristic variation, according to Bate- 

 son's terminology, and usually appears 

 as a form of discontinuous variation; it 

 can not be considered in itself a fact of 

 atavism, a phenomenon of reversion, 

 but at the most a phenomenon of 



arrested development. I should note 

 that Dependorf has recently also com- 

 bated, to a certain extent, the explana- 

 tion of atavism for supernumerary 

 teeth, in which the idea of reversion 

 is much more easily sustained than in 

 agenesia, considering the phylogenetic 

 evolution of the dental system from the 

 lower to the higher vertebrates. 



The congenital absence of incisors is 

 in a way a teratological phenomenon, 

 inasmuch as it appears unexpectedly 

 in a given individual of the species, 

 and no equivalent condition is found in 

 the most closely related species; and 

 it is particularly teratological in char- 

 acter if it is coupled with similar 

 occurrences in the molar teeth. But 

 at the same time, it is also a progressive 

 phenomenon when it follows a law of 

 evolution : so that the fact of lack of cer- 

 tain teeth can have different meanings 

 according to the number or type of 

 teeth wanting. It seems to me that the 

 lack of the superior lateral incisors in 

 man (or the presence of extra ones) 

 indicates a new step in the so-called 

 regressive evolution of the dental sys- 

 tem, just as does the disappearance of 

 the third molar (the wisdom tooth.) 



EXPLANATION OF THE CONDITION. 



Amadei in 1881 proposed the hypoth* 

 esis that the same movement of 

 evolution which tends to cause the 

 disappearance of the last molar would 

 make its action felt on the entire jaw, 

 but particularly at its two centers of 

 reduction: one corresponding to the 

 location of the third molar and the 

 other at the point where the lateral 



^Translation and abridgment of "Mancanza congenita ed ereditaria di un incisivo," in Atti 

 della Societa Romana di Antropologia, Vol. XV, p. 395, 1909. 



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