202 ARBOREAL MAN 



It is not so completely helpless as is the typical inhabitant 

 of an arboreal nest, nor is it hatched perfected for arboreal 

 life, but it exhibits just that ability for early terrestrial 

 enterprise that the typical terrestrially hatched members 

 of its family possess. 



It is this retention of the old terrestrial adaptation of 

 the young that causes a defect in this otherwise singularly 

 successful assumption of arboreal habit, for the dangerous 

 degree of ability in terrestrial enterprise, which the young 

 still possesses, leads at times to its early destruction by 

 falling from the branch. No doubt there are good 

 reasons probably in the shape of land-crabs and rats 

 for the adoption of this strange nesting habit by Gygis 

 Candida, but, even were there no typical Terns in which 

 the ancestral customs could be studied, an examination 

 of the young would at once reveal the fact that the 

 parental arboreal life was a comparatively recent assump- 

 tion by the species. As the baby White Tern shows so 

 well its terrestrial inheritance, whilst its parents are so 

 perfectly adapted to an arboreal life, it is not unlikely 

 that the human baby will show its arboreal inheritance 

 better than its terrestrially modified parent. 



We will first turn to so obvious a point as the relative 

 lengths of the arm and leg. In typical arboreal Primates 

 the arm is longer than the leg, and in some forms, such 

 as the Orang-utan, the disproportion is very well marked. 

 This disproportion may be expressed by means of an 

 " intermembral index," which, without further discussion, 

 we may accept as an arithmetical expression of the 

 relation of fore and hind limb lengths, which is high 

 when the arm is relatively long, and low when it is rela- 

 tively short. In the Orang-utan this index is about 140, 

 in the Gorilla about 118, and in the Chimpanzee only 104. 

 In adult Man the alteration has been so great that, 

 though the index is as high as 83*6 for the Bambute 

 Pygmies (Shrubshall), it averages no more than 67 in 

 most Europeans (Duckworth). 



