290 SECRETS OF ANIMAL LIFE 



thumb and big toe for branch-gripping purposes. 

 Dr. Wood Jones sets one thinking when he notes 

 that some rodents (e.g. the tree mouse, Mus 

 ramgarettce, discovered by Dr. Charles Hose in 

 Borneo) have developed very perfectly opposable 

 thumbs and big toes upon lines exactly similar to 

 the Primates. For this phenomenon of "con- 

 vergence " the attainment of closely similar adap- 

 tations by unrelated types is of surpassing interest. 

 We have dealt with it in a previous study, and 

 referred to the discussion of the problem by Profes- 

 sor Arthur Willey in his Convergence in Evolution 

 (1912), and also by Professor Henri Bergson in his 

 Creative Evolution (1911), but the whole riddle 

 has not yet been read. 



The evolution of a free hand, able to grasp the 

 food and lift it to the mouth, made it possible to 

 dispense with protrusive lips and gripping teeth, 

 and thus there began the recession of the snout 

 region, and the correlated enlargement of the brain 

 box and the bringing of the eyes to the front. There 

 is often a tax to pay for great improvements, and 

 " the process of shortening of the snout, outstrip- 

 ping the process of reduction of the dental series, 

 gives rise to one of the great problems of modern 

 dentistry the proper treatment of the many evils 

 arising from overcrowded jaws/' Moreover, with 

 the reduction of the lower jaw modern man seems 

 to be in some danger of losing his chin, and Profes- 

 sor Wood Jones does not look with pleasure at the 

 prospect of " the dawn of a chinless aristocracy." 



