174 



MENTAL EVOLUTION IN ANIMALS. 



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we so regard tlie exhibitions of erotomania, infanticidal mania, 

 &c., which occnr in animals perhaps more frequently than 

 they do in man. 



But with reference to the imperfection of instinct, we 

 have now some more important matters to consider than the 

 mere enumeration of cases in wliich instinct may have been 

 observed at fault. Let it first be observed that under the 

 general heading *' Imperfection of Instinct," we may include 

 two very different classes of phenomena ; for instincts may 

 be imperfect because tliey have not yet been completely 

 developed, or they may appear to be imperfect because not 

 completely answering to some change in those circumstances 

 of life with reference to which they have been fully developed. 

 Now, if instincts have been developed at all, it is obvious 

 that they must have passed through various stages of imper- 

 fection before they attained to perfection, and therefore we 

 might expect to meet with some cases of instinct not yet per- 

 fected — cases, be it observed, which differ from those already 

 mentioned, in that their faultiness arises, not from a novelty 

 of experience with reference to v/hich the instinct has not 

 been developed, but from the fact of the instinct not being 

 yet fully formed ; and this ought more especially to be the 

 case with instincts the perfection of which is not of vital 

 importance to the species ; for such instincts would not have 

 been so rigorously trained or perfected by natural selection. 

 A good illustration on this head seems to be afforded by the 

 instinct of destroying the drones as exhibited by the hive-bee. 

 Thus, to quote from " Animal Intelligence " : — " Evidently 

 the object of this massacre is that of getting rid of useless 

 mouths ; but there is the more difficult question as to why 

 these useless mouths ever came into existence. It has been 

 suggested that the enormous disproportion between the pre- 

 sent number of males and the single fertile female, refers to 

 a time before the social instincts became so complex or con- 

 solidated, and when, therefore, bees lived in lesser communi- 

 ties. Prol^ably this is the explanation, altliough 1 think we 

 might still have expected that before this period in their 

 evolution had arrived bees might have developed a compen- 

 sating instinct, either not to allow the queen to lay so many 

 drone eggs, or else to massacre the drones while still in the 

 larval state. We must remember, also, that among the wasps 



