322 PRESENT PROBLEMS IN EVOLUTION AND HEREDITY. 



(ui. 3) large uiid cut long- before the traditional years of discretion, but 

 in the tirst two lower molars are found two intermediate cusps (Tomes)* 

 wbicli are variable or absent in us (Abbott); moreover, in the macro- 

 dont races a surplus molar t (m. 4) is sometimes developed. ]\Iummery 

 reports nine such cases among 328 West Africans (Ashantis). As an 

 instance of associated habit I may here mention that Dr. Lumholtz, 

 the Australian explorer, informs me that in adult natives the teeth are 

 worn to the gum ; in the iibsence of tools they are used in every occu- 

 pation, from eviscerating a snake to cutting a root. A tour of inspec- 

 tion through any large collection of skulls brings out the contrast be- 

 tween the sound and hard- worn uu>lars of tlie savage, and the decayed 

 and little-worn molars of the wliite. 



Upon the descent theory, the reduction of teeth in the progenitor of 

 man began as far back as the Eocene period, for not later than that 

 remote age do we hud the full complenuMit of three incisors and four 

 premolars in each jaw; now there are but two remaining of each. 

 Baiime, a high authority, believes he has discovered eleven cases of a 

 rudimental reversion of one of these lost premolars | not cutting the 

 jaw. Not infrequently both these missing teeth occur by reversion. 

 It is difficult to conceive of reversion to such a remote period, yet it 

 is supported by other evidence. An embryonic third incisor has, I 

 believe, been discovered. As long ago as 1863 Sedgwick § recorded a 

 case of six upper and lower incisors m both jaws, and appearing in 

 both the milk and permanent dentitions; this anomaly was inherited 

 from a grandparent, a striking instance of hereditary reversional ten- 

 dency. We might consider that these cases of supernumerary teeth 

 belong in the same category as polydactylism, or additional fingers, 

 wliich are not ataAistic, but for the taijt that they do not exceed the 

 typical ancestral number, whereas the fingers do. 



We owe to Windle|| a careful review of the incisor reversions, in 

 which he shows that the lost incisors re-appear more frequently in the 

 upper than the lower jaw (coinciding with the fact that the lower teeth 

 were the first to disappear in the race); he considers that the ttst 

 tooth was the one originally next the canine, and concludes by adding 

 our present upper outer incisor to the long list of degenerating organs.^] 

 He supports this statement by measurements and by citing cases in 

 which it has been found absent. Yet the reduction of the jaws is ap- 

 parently outstripping that of the teeth, if we can judge from the 



* Dental Audtomy, p. IKi. 



t This tooth lias been found in several otlier niacrodunt tribes (Australians, Tas- 

 mauiaus, Neo-Caledouiaus), Fontan. 



t Odontologisdie FortfchuiKjeii, p. 268. This rudiment is found between the hrst and 

 second normal premolars. 



^ British and Foreign Medico Chirurgical Review, 18(io. 



\\ Journal of Anaiomg and Fktjmolog II, 1S87. p. 85. 



1l BaunKi believes that the missing incisor is tlie primitive median one, while Tur- 

 ner believes it is the second. The fossil record supports VVindle. 



