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 
ramgarette, 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.” 
