178 MENTAL EVOLUTION IN ANIMALS. 



manent instincts. Just as in the life-time of the individual 

 adjustive actions which were originally intelligent may by 

 frequent repetition become automatic, so in the life-time of. 

 the species actions originally intelligent may, by frequent 

 repetition and heredity, so write their effects on the nervous 

 system that the latter is prepared, even before individual 

 experience, to perform adjustive actions mechanically which 

 in previous generations were performed intelligently. This 

 mode of origin of instincts has been appropriately called the 

 " lapsing of intelligence."* 



Tor the sake of subsequent reference, I shall allude to 

 instincts which arise by way of natural selection, without the 

 intervention of intelligence, as Primary Instincts, and to 

 those which are formed by the lapsing of intelligence as 

 Sscondary Instincts. 



Let us now consider the reasons which a priori lead us to 

 assign the probable origin of instincts to these principles. 

 Taking first the case of primary instincts, these reasons may 

 be briefly rendered thus : — 



(1.) Many instinctive actions are performed by animals 

 too low in the scale to admit of our supposing that the adjust- 

 ments which are now instinctive can ever have been intel- 

 ligent. (2.) Among the higher animals instinctive actions 

 are performed at an age before intelligence, or power of 

 learning by individual experience, has begun to assert itself. 

 (3.) Considering the great importance of instincts to species, 

 we are prepared to expect that they must be in large part 

 subject to the influence of natural selection. As Mr. Darwin 

 observes, " it will be universally admitted that instincts are 

 as important as corporeal structures for the welfare of each 

 species under its present conditions of life. Under changed 

 conditions of life it is at least possible that slight modifica- 

 tions of instinct might be profitable to a species ; and if it 

 can be shown that instincts do vary ever so little, then I can 

 see no difficulty in natural selection preserving and con- 

 tinually accumulating variations of instinct to any extent 

 that was profitable." 



That instincts may arise by way of lapsed intelligence is 

 rendered probable a priori by all the facts which show the 

 resemblance between instincts and intelligent habits. To 

 take only a few of these facts for the present purpose, I 



* By Lewes, see Problems of Life and Mind. 



