1088 Growth, its Conditions and Variations, [Nove 
evolution. Through the persistent exercise of these faculties mat, 
while retaining in strong measure the three life purposes of te $ 
lower animals, has added to them many others of a higher grade. 
But the faculties which have led to man’s mental evolution 
exist only undeveloped or but slightly developed in the lower 
life kingdom, and the whole vigor of these lower creatures is 
given to the purposes named. 
These purposes in reality may be reduced to two. , Assault 
and defence are devoted to a single end, the preservation of ind- 
vidual life. Reproductive activity is devoted to another end, the 
preservation of race life. These two purposes are, to a consider | 
able extent, in opposition. The animal that is efficient in either 
is apt to be deficient in the other. The one great object tobe 
attained is life continuance. Any animal tribe that declines m- 
both nutritive and reproductive powers dies out. Only those a | 
are successful in one of these powers can hold their here j 
life struggle. But it is simply impossible that any tribe e 
markedly successful in both these directions, for two y 
the first place great reproductive powers interfere with ee 
food taking, by increasing the number of applicants for the gos 
supply. It sets up a struggle for existence within the ta Bare, 
the tribe itself. In the second place there is a physiological o 
position, a struggle for existence between the powers desi T 
vidual. Great activity in food getting reduces the a 
energy. Great reproductive vigor exhausts the muscular " 
nervous strength, Thus no animal can possess sapeti 
both these directions, and to the extent that it succeeds in . 
direction, its powers must decline in the other. ; d k 
This opposition is displayed throughout the whole ranp e 
animal kingdom. As a general rule the smaller and re ae 
lived the animal the greater its fecundity. But smal aa p 
short life indicate that its powers of obtaining nutri 
ited, or that its destruction by enemies is great. ‘The, e orale 
existence of the tribe, in this case, can only be gained z are 
reproduction. Again, some animals kave efficient food 8” 
powers while in the larval state, as in the case of ce ai 
larve, while their nutritive advantages are greatly reduce t a 
mature state. In such cases we find the larve to feed ane w 
rapidly, while the imago scarcely feeds at all, but deve” : 
. 
powers to reproduction, But in the case of certain Ins 
