214 ARBOREAL MAN 



The same story could be told of every condition of 

 distinctive environment. Some animals have acquired 

 a highly useful power of burrowing in the earth for the 

 purpose of making safe retreats for themselves and their 

 young, or for obtaining food below the surface of the 

 earth; some animals have become highly specialized 

 slaves to this habit. The Insectivorous Moles (Talpidce), 

 the Golden Moles {Chrysochloridce), the Rodent Mole Rats 

 (Spalacidce), and the marsupial Notoryctes, are examples 

 of highly s^Decialized failures in this direction. 



It is not likely that a habitat so attractive and so 

 universally present as the tree-tops would fail to be 

 abused by some members of the stocks which have taken 

 possession of it. It is the distinction of the human stock 

 — a distinction to which we have had frequent occasion 

 to allude — that it never became the slave of its arboreal 

 environment, for it became adapted to tree life in a 

 strictly tempered manner, and it specialized to the 

 successful minimum degree. 



It will be best to note the particular specializations 

 which arboreal animals are likely to develop to such an 

 extent as to imperil their future evolutionary progress. 

 First are those special adaptations for clinging tight to 

 branches, securing for the animal a high degree of arboreal 

 safety at the initial expense of some of its activity. The 

 more the clinging adaptations are developed the more 

 hampered become the real climbing powers, and the less 

 the chance of producing a truly emancipated fore-limb. 

 All four climbing limbs become clinging limbs, the grasp- 

 ing hands and feet become alike mere claw-like adapta- 

 tions of the members to the branches, and even claws 

 and nails may turn into hooks. 



Phascolarctus, among the Metatheria, is a mere arboreal 

 dinger w^ith activities greatly reduced, and its educational 

 possibilities almost gone. It possesses an opposable big 

 toe, but its hand has undergone a change reminiscent of 

 ventures seen in avian and reptilian orders, for the thumb 



