Chap. IV. MANNER OF DEVELOPMENT. 107 



CHAPTEE IV. 



On the Manner of Development of Man from some 



lower Form. 



Variability of body and mind in man — Inheritance — Causes of 

 variability — Laws of variation the same in man as in the lower 

 animals — Direct action of the conditions of life — Effects of the 

 increased use and disuse of parts — Arrested development — Re- 

 version — Correlated variation — Rate of increase — Checks to 

 increase — Natural selection — Man the most dominant animal 

 in the world — Importance of his corporeal structure — The 

 causes which have led to his becoming erect — Consequent changes 

 of structure — Decrease in size of the canine teeth — Increased 

 size and altered shape of the skull — Nakedness — AbseDce of 

 a tail — Defenceless condition of man. 



We have seen in the first chapter that the home-logical 

 structure of man, his embryological development and 

 the rudiments which he still retains, all declare in the 

 plainest manner that he is descended from some lower 

 form. The possession of exalted mental powers is no 

 insuperable objection to this conclusion. In order that 

 an ape-like creature should have been transformed into 

 man, it is necessary that this early form, as well as 

 many successive links, should all have varied in mind 

 and body. It is impossible to obtain direct evidence on 

 this head; but if it can.be shewn that man now varies 

 — that his variations are induced by the same general 

 causes, and obey the same general laws, as in the case 

 of the lower animals — there can be little doubt that 

 the preceding intermediate links varied in a like 

 maimer. The variations at each successive stage of 

 descent must, also, have been in some manner accumu- 

 lated and fixed. 



