GENESIS. 237 



when the rate of growth is much decreased by the compara- 

 tively rapid increase of expenditure — when the excess of 

 assimilative power is diminishing in such a way as to indi- 

 cate its approaching disappearance ; it becomes needful for 

 the maintenance of the species, that this excess shall be 

 turned to the production of new individuals ; since, did 

 growth continue until this excess disappeared through the 

 complete balancing of assimilation and expenditure, the pro- 

 duction of new individuals would be either impossible or fatal 

 to the parent. And it is clear that "natural selection " will 

 continually tend to determine the period at which gamo- 

 genesis commences, in such a way as most favours the main- 

 tenance of the race. 



Here, too, may fitly be pointed out the fact, that, by 

 61 natural selection," there will in every case be produced, the 

 most advantageous proportion of males and females. If the 

 conditions of life are such as to render a greater or less in- 

 equality of the sexes beneficial to the species, in respect 

 either of the number of the offspring, or the character of the 

 offspring ; then, those varieties of the species which, from any 

 cause, approach more than other varieties towards this 

 beneficial degree of inequality, will be apt to supplant other 

 varieties. And conversely, where equality in the number of 

 males and females is beneficial, the equilibrium will be main- 

 tained by the dying out of such varieties as produce offspring 

 among which the sexes are not balanced. 



