138 INSTINCT AND EEASON. 



of his presence, ' their thirst for water quite overcoming their 

 sense of danger. 3 Hunger constantly conquers the fear of 

 man in the robin, as does in other birds the sense of immi- 

 nent danger. In both cases the bird confidingly seeks the 

 shelter or food-supply of man's dwelling or person. The 

 instinct of self-preservation is often overcome by voracity in 

 animals, like certain vultures, given to gorging themselves to 

 repletion with animal food. But those instincts also which 

 are more purely moral or mental such as sympathy, gene- 

 rosity, benevolence, or charity frequently conquer the purely 

 physical instincts of fear of danger or love of life. The 

 migratory instinct is more powerful than the maternal, lead- 

 ing parent birds to desert their young broods (Darwin and 

 Adams). This collision of the migratory and maternal in- 

 stincts, and dominance of the former, frequently occurs, for 

 instance, in the swallow (Nichols). 



While many instincts are intelligible probably from their 

 simplicity and natural relationships such as motherly love, 

 self-preservation, or imitation others do not at present ad- 

 mit of satisfactory explanation ; for instance, certain forms 

 of way-finding over previously untraversed ground. This 

 class of dubious instincts is fully illustrated in the chapter 

 on ' Unsolved Problems.' 



The number of instincts in a given individual, species, 

 genus, or class depends, of course, on the view taken of what 

 is or constitutes an instinct. Kirby and Spence regard the 

 determination of the number of separate instincts among 

 insects as an insoluble problem. Among nurses alone in 

 bees these authors describe or refer to thirty distinct in- 

 stincts, and they infer therefrom that the flexibility, plasti- 

 city, or variability of instinct is greater in insects than in 

 higher animals. Different instincts occur in different castes 

 of the same species or community for instance, in ants 

 (Houzeau) and there are special instincts in different breeds 

 of domestic animals, such as the dog, both breeds and in- 

 stincts being gradually developed by man's selection and 

 culture. 



So long as it is impossible satisfactorily to define instinct 

 and reason so long at least as we possess no satisfactory 



