Chap. IT. 
MANNER OF DEVELOPMENT. 
107 
CHAPTER 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 — Absence of 
a tail — Defenceless condition of man. 
We have seen in the first chapter that the homological 
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 
manner. The variations at each successive stage of 
descent must, also, have been in some manner accumu- 
lated and fixed. 
