456 Animal Life and Intelligence. 



under changed circumstances in a given direction, may 

 tend to draw the habits of all the members of the com- 

 munity in that given direction. 



And with regard to the more general question of the 

 variation of habits and instincts, we may say that, in 

 addition to those variations in the origin and direction of 

 which intelligence is a factor, there are other variations 

 which take their origin without the influence of intelligence 

 under the stress of changing circumstances, and yet others 

 which may arise as we say " fortuitively " or "by chance," 

 that is, from some cause or causes whereof we are at 

 present ignorant, and which do not appear to be evoked 

 directly by the stress of environing circumstances. 



Granting, however, the existence of these variations in 

 whatsoever way arising, and granting the influence of 

 natural selection, of sexual selection, and perhaps of the 

 inheritance of individually acquired modifications, those 

 variations which are for the good of the race or species in 

 which they occur will have a tendency to be perpetuated, 

 while those which are detrimental will be weeded out and 

 will tend to disappear. 



Passing on now to consider the characteristics of those 

 activities which we term "intelligent," we may first notice 

 what Mr. Charles Mercier, in " The Nervous System and 

 the Mind," calls the four criteria of intelligence. Intelli- 

 gence is manifested, he says, first, in the novelty of the 

 adjustments to external circumstances ; secondly, in the 

 complexity; thirdly, in the precision; and fourthly, in 

 dealing with the circumstances in such a way as to extract 

 from them the maximum of benefit. 



Now, I think it is clear that, when it is our object to 

 distinguish intelligent from instinctive activities, the pre- 

 cision of the adjustment cannot be regarded as a criterion 

 of intelligence. Many instinctive acts are wonderfully pre- 

 cise. The sphex is said to stab the spider it desires to 

 paralyze with unerring aim in the central nerve-ganglion. 

 Other species, which paralyze crickets and caterpillars, 

 pierce them in three and nine places respectively, according 



