226 INITIATIVE IN EVOLUTION 



In an animal covered with thick hair the sensory impulse conveyed 

 might be exceedingly delicate, but, from the nature of the case, 

 of much more limited range than in one like man in whom the hair 

 is so greatly diminished in length and thickness. 



It would be fruitless to speculate as to which of these four 

 forms of stimuli was the earliest to become effective in 

 developing man. 



Cold and Pain. 



Two of them, cold and pain, may be termed nocuous ; one, 

 that of touch, useful, and one, that of warmth, indifferent. If it be 

 true, as Professor Scott Elliott states, 1 that man's earliest home had 

 a climate which " lies between the regular tropical, with wet, 

 steaming, impassable jungles, and the colder temperate zone, so 

 affording chance of acclimatisation in both directions," the stimuli 

 of cold would even then not be wanting, however much they 

 increased in severity when he passed through glacial periods ; but 

 wherever, whenever, and at whatever time he first became man 

 he had to tread the Via Dolorosa in the course of his hard and event- 

 ful life, and must have been well accustomed in all regions of his 

 skin to the stimuli of pain, working, as he did, for his living, and 

 fighting for it and his mate, with varied and powerful enemies. 

 Though it is correct to call both these fundamental stimuli 

 " nocuous," this is all a matter of degree, and both the stimulus of 

 moderate cold, raising blood -pressure and activating metabolism, 

 and that of minor pains, would do little else than good in his 

 education for the higher terrestrial life to which he had descended. 

 If he was to learn effectually to take care of himself the discipline 

 of both moderate cold and pain would be as valuable to him then as 

 in its measure it is to his descendant to-day. The triumphs of 

 medicine and surgery could never have appeared if it were not for 

 the beneficent warning voice of pain that so generally accompanies 

 disease. 



Through long ages of exposure to the stimuli of cold and pain 

 came response in the form of cold and pain spots, after minute 

 struggles between the static conservative tissues of the skin and the 

 dynamic force of repeated assaults upon them. In due time then 

 receptors appeared and each became connected with the central 

 organs, by which means better adapted motor reactions against 

 " nocuous " cold and pain became possible. In 1900 Professor 

 Sherrington summed up the evidence in Schaf er's Vv ork on Physiology 

 against the existence " of separate afferent fibres with their specific 



1 Prehistoric Man and His Story, p. 92. 



