140 MENTAL EVOLUTION IN ANIMALS. 



Perception arises out of Eeflex Action, Eeflex Action out of 

 Perception, or whether tliere is any genetic continuity be- 

 tween the two at all. This is a most difficult question, and 

 one which I do not think we are as yet entitled to answer 

 with any kind of scientific confidence. 



According to Mr. Spencer the perceptive faculties arise 

 out of the reflex when these attain a certain level of intricacy 

 in their structure, or a certain degree of rarity in their occur- 

 rence. Thus he says, " When, as a consequence of advancing 

 complexity and decreasing frequency in the groups of external 

 relations responded to, there arise groups of internal relations 

 which are imperfectly organized and fall short of automatic 

 regularity ; then, what we call Memory, becomes nascent."* 

 But as a matter of fact it seems, I think, very questionable 

 whether the only factors which lead to the differentiating of 

 psychical nervous processes from reflex nervous processes 

 are thus complexity of opei^ation combined with infrequency 

 of occurrence. For it is obvious that in ourselves certain 

 truly reflex actions are of immense intricacy and of exceed- 

 ingly rare occurrence — such, for example, as vomiting and 

 parturition. The truth is that, so far as definite knowledge 

 entitles us to say anything, the only constant physiological 

 difference between a nervous process accompanied by con- 

 sciousness and a nervous process not so accompanied, is that 

 of time. In very many cases, no doubt, this difference may 

 be caused by the intricacy or by the novelty of the nervous 

 process which is accompanied by consciousness ; but, for the 

 reason which I have given, I do not think we are justified in 

 concluding that these are the only factors, although I have 

 no doubt that they are highly important factors. For all 

 that we know to the contrary, natural selection or other 

 causes may have determined the physiological conditions 

 necessary to the rise of consciousness (and so to the perception 

 of pleasure and pain), without any question as to intricacy 

 or infrequency being concerned ; in which case the time- 

 relations needed to meet these conditions would have become 

 evolved together with them. And I think it speaks in favour 

 of some such view as this that the structure of the cerebral 

 hemispheres is in some respects strikingly unlike the structure 

 of the reflex centres. 



Be the factors what they may, however, it is a great 



* Frinciples of Psychology ^ voL i, p. 446. 



