204 The Science of Life. 



stimulus other than that of the persistence of the essen- 

 tial conditions of life. 



Slightly higher are the simple reflexes which may be 

 performed without the co-operation of the higher brain- 

 centres, and are also independent of conscious control. 

 Swallowing and sneezing are familiar examples. 



Higher still are complex reflexes, illustrated especially 

 in often-repeated activities which were never under intel- 

 ligent control. These are habitual, but they have a 

 different origin from the habitual-intelligent activities 

 above referred to. According to many, the instincts of 

 ants and bees, for instance, are nothing more than very 

 complex reflexes, but it is doubtful whether we ever get 

 quite near enough to them to detect the individual 

 variations which may give them intelligent (as well as 

 instinctive) character. 



In the middle of this inclined plane between habitual- 

 intelligent activities and complex reflexes we may place 

 instinctive activities. They differ from habitual-intelli- 

 gent activities in being inborn or innate, requiring no 

 experience nor education, though they are often per- 

 fected thereby. They are also shared by all the members 

 of the species in almost the same degree, and biologi- 

 cally they are of critical moment in the struggle for 

 existence. They differ from complex reflexes in involv- 

 ing the activity of the higher nerve-centres, and it is 

 probable, though not exactly demonstrable, that they 

 are associated with consciousness. 



Our metaphor of the inclined plane emphasizes the 

 probability that there are no hard-and-fast lines sepa- 

 rating the different grades of activity from one another. 



The theory of instinct which was dominant before 

 Darwin's day may be conveniently termed Lamarckian. 

 Lamarckian ^ interpreted instincts as the outcrop of in- 

 Theoryof herited habits. By " lapsing of intelligence", 

 instinct. as Q H L ewes termed it, activities which 

 originally demanded intelligent control may become 

 habitual, and it was supposed that in the course of 

 generations these habits might become engrained in 

 the constitution; in short, inheritable. Similarly, com- 

 plex reflex actions becoming habitual might also give 



