" ARBOREAL MAN " 219 



do. or they may even climb in the proper sense of the word, but in this 

 climbing the grip is not obtained by the application of the palmar surface 

 of the hand, but by the hook-like action of claws and nails ; this method 

 is practised by many of the Carnivora. The maximum of possibilities 

 is not attainable in any of these cases. It is not enough to have a thoroughly 

 emancipated fore -limb, it is not enough to be thoroughly arboreal. 

 It was a combination of seemingly humble and unimportant circumstances, 

 acting at the very dawn of mammalian life, which permitted the 

 emancipation of an unmodified fore-limb in a certain stock, and so laid 

 the direct path for the evolution of the highest Mammals and Man. 

 (Italics mine.) 



But, in point of Bio-sociality, carnivora usually climb trees 

 for a totally different purpose from that animating symbiotic 

 animals. Their " industry " is not one requiring honest specialisa- 

 tion, and, in the absence of such, they become " over specialised," 

 tending towards " Contre-E volution." Their appetite lures 

 them to mere expediency of specialisation, and this is not enough 

 to achieve the highest results in evolution. It is not enough, 

 I should say, to possess an appetite. What is needed, is that 

 happy mean of appetite which is most consistent with the per- 

 formance of patient and systematic services and duties. And an 

 appetite thus " controlled " is yet most likely to be rewarded 

 by a complete diet one that powerfully, if unobtrusively, aids 

 the realisation of a maximum of possibilities. Is there anything 

 to contradict these conclusions ? Is there any other explanation 

 which accounts with equal cogency for the facts confronting 

 us here ? 



In support of my contention that it was originally and most 

 potently the attraction and also the high physiological value of 

 the spare products of the trees which determined the evolution 

 of arboreal habits, I would instance the case of so lowly a creature 

 as Birgus latro, a crab which climbs trees in search of Pandanus 

 and other fruits, and even of cocoanuts. This Decapod was 

 evidently allured and assisted to a terrestrial habitat by a cross- 

 feeding taste, and with the aid of the aforesaid diet it has managed 

 to live permanently upon the land. Birgus latro shows a com- 

 paratively high perfection of respiratory arrangements, and, 

 altogether, the order of the Decapods includes the highest forms 

 of the entire class of the Crustaceans. Other things equal, 

 therefore, cross-feeding represents everywhere the superior habit 

 of life, one that is pregnant with possibilities of progressive 

 evolution. 



