MAN’S ARBOREAL APPRENTICESHIP 293 
It may be objected that many marsupials are 
arboreal, and yet they do not seem to have made 
much of their educational opportunities. But the 
answer is that the ground-plan of the marsupial 
brain is different from that of placental mammals 
and precluded great advance. As to the problem 
whether improvement in brains brought about an 
increasing manual dexterity, or whether bodily 
improvements made possible a cerebral advance, 
Professor Wood Jones gives the right answer, that 
the two sets of improvements went hand in hand. 
“The evolution of the free and mobile fore limb 
in arboreal life may be likened to the production of 
a musical instrument—an instrument upon which it 
is impossible for the animal to produce a full range 
of harmony, or to appreciate the psychical connota- 
tions of this harmony, unless adequate cerebration 
is developed coincidently.” Perhaps a somewhat 
similar answer may be given to the question that 
confronts us at every turn: How all these adapta- 
tions to arboreal life could arise if functional modi- 
fications acquired by individuals are not entailed 
as part of the inheritance of the race. From the 
fountain of change hidden in the dark recesses of 
the germ-cells there is a welling forth of tentatives 
and initiatives, but it rests with the explicit organism 
as a genuine agent to put these variations and 
mutations to the test, for if this is not done they will 
profit nothing, and, being born before their time, 
will disappear unappreciated. 
