POPULAR SCIENCE 99 



that the three apes are equidistant from man, this result would 

 make it certain that the common ancestor lived before the 

 appearance of the large apes in the Miocene, for no one would 

 look upon the orang as being the parent of the gorilla, or vice 

 versa. As to the common susceptibility to malaria, syphilis, 

 bilharziosis, and similar diseases, it is too soon to make any 

 dogmatic statement as to the degree of kinship implied. The 

 experts who know most about the Wassermann test are cautious 

 in accepting any theory of the action of complement and 

 amboceptors as being final. At present it may be asked if 

 any known facts about men and monkeys are more suggestive 

 than the relationship which is demonstrated by vaccination 

 between the child and the calf. We do not even know why 

 red-haired people should be specially subject to rheumatism. 



Lastly, it is always assumed that disease alone can cause 

 atrophy — the use of weapons for fighting and killing by early 

 man led to the disuse of the canine teeth, and the consequent 

 reduction in the size of the teeth led to a decrease in the size 

 of the jaws, " as we may feel almost sure from innumerable 

 analogous cases. In a future chapter we shall meet with a 

 closely parallel case in the reduction or complete disappearance 

 of the canine teeth in male ruminants apparently in relation 

 with the development of their horns ; and in horses in relation 

 to their fighting with the incisor teeth and hoofs." ^ In all 

 herbivora the large canines are a handicap because they prevent 

 any side-to-side play between the upper and lower molar teeth. 

 The original canines of the Condylarthra have disappeared in 

 order to allow the herbivora full use of the molars ; that is, 

 horns were acquired because the canines were lost, not vice 

 versa. In rumination the lower jaw is swung as much as two 

 inches from side to side. The survival-value of good molars 

 in such animals is seen in the case of some breeds of dairy cows 

 in which the lower jaw has become so narrow that many of 

 them have become " bad doers," that is, they cannot masticate 

 the food sufficiently to maintain the highest condition of health. 

 The large canines of the musk deer, pig, and hippo form a 

 separate problem, as they grow from persistent pulps. 



Other examples of handicap are seen in the lost tail and 

 projecting great toe of some monkeys, the legs of snakes, wings 

 of apteryx and ostrich, and the legs of the whale. The small 

 eyes of the mole and cave-dwellers are to be explained by the 

 fact that a large eye offers a very easy way of severe injury, 

 and that it is therefore only justified by its utility. The loss 

 of the lateral toes in hoofed animals is obviously useful. The 

 disappearance of the body of the scale insect, of the organs of 

 many parasites, the atrophy of unused muscles, and the loss 



^ Darwin, Descent of Man, p. 53. 



