" ARBOREAL MAN " 223 



but it could not do all, without the accompanying passive specialisation 

 of the hind-limb. Mere abilty in climbing, which usurped the power 

 of any real ability to walk, was but a poor accomplishment, for to complete 

 the whole story of evolution the animal which climbed up the tree had 

 still to walk down and the Old-World apes still show in caricature how 

 this was done. 



In other words, given auspicious (physiological and correlated) 

 mechanical conditions, a highly beneficial " reciprocal differ- 

 entiation " could take place between fore and hind limbs a high 

 form of " domestic " Symbiosis, which, as we have seen, 

 indispensably depends upon biological Symbiosis. 



Service and progress through Symbiosis being the chief aims 

 of Nature, there was no need that all the limbs should specialise 

 for the grasping and handling of the food. Enough if the fore- 

 limb so excelled. The hind-limb could not do better than adapt 

 itself reciprocally. 



Prof. Wood Jones's explanation, no doubt, is still too purely 

 anatomical. At best we only dimly perceive that some auspicious 

 extra factor has favoured the reciprocal differentiation of the 

 members as pictured. What that factor is, however, does not 

 emerge. It was not the fresh air of the tree-tops, for that was 

 accessible to those which turned quadrumanous quite as well 

 as to those animals for which a happier destiny was to be provided. 

 Was it Luck ? Or was it Cunning ? The case becomes intelligible 

 if we regard it as representing a thorough and advanced applica- 

 tion of the " law of the members." Man's progenitor apparently 

 was one who excelled in biological righteousness, which gave 

 scope to a number of beneficial principles, physiological, 

 anatomical and sociological, to become operative towards the 

 exaltation of his type. 



With regard to the evolution of the hind-limb, the author 

 thinks that m its case stability became substituted at an early 

 date for mobility, telling us that 



environmental conditions could not combine to free the hind -limb of its 

 duty of supporting the body weight and yet preserve it in full functional 

 activity ; the arboreal habit did this for the fore-limb, but there was no 

 life circumstance that could do the same thing for the hind-limb. 



I should say that the main contingencies of life were such as 

 to render unnecessary a great specialisation of the hind-limb. 

 All that was necessary was that it remained in due complemental 

 relation to the fore-limb, which, being emancipated according 



