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  ANIMAL 
  BEHAVIOUR 
  

  

  there 
  are 
  different 
  grades 
  of 
  instinctive 
  behaviour. 
  There 
  

   are 
  three 
  main 
  theories 
  at 
  present 
  in 
  the 
  field. 
  (A) 
  Some 
  

   investigators 
  rank 
  instinctive 
  behaviour 
  as 
  closely 
  comparable 
  

   to 
  chains 
  of 
  reflex 
  actions, 
  and 
  as 
  due 
  to 
  non-cognitive 
  hered- 
  

   itary 
  predispositions 
  to 
  follow 
  a 
  certain 
  routine 
  when 
  a 
  

   number 
  of 
  stimuli 
  present 
  themselves. 
  (B) 
  Others 
  regard 
  

   instinctive 
  behaviour 
  as 
  quite 
  inseparable 
  from 
  intelligent 
  be-, 
  

   haviour. 
  (C) 
  According 
  to 
  a 
  third 
  view, 
  instinct 
  and 
  in- 
  

   telligence 
  are 
  two 
  radically 
  different 
  though 
  often 
  co-opera- 
  

   tive 
  kinds 
  of 
  knowing, 
  which 
  have 
  evolved 
  along 
  divergent 
  

   lines. 
  

  

  (A) 
  Some 
  investigators 
  rank 
  instinctive 
  behaviour 
  as 
  near 
  

   compound 
  reflex 
  actions, 
  as 
  the 
  outcome 
  of 
  non-cognitive 
  

   hereditary 
  impulsions 
  or 
  predispositions 
  to 
  enter 
  upon 
  a 
  

   certain 
  routine 
  when 
  a 
  certain 
  trigger 
  is 
  pulled, 
  and 
  to 
  follow 
  

   on 
  in 
  a 
  perfectly 
  definite 
  manner, 
  the 
  result 
  of 
  one 
  trigger- 
  

   pulling 
  leading 
  to 
  another 
  trigger, 
  and 
  so 
  on. 
  This 
  may 
  be 
  

   called 
  the 
  reflex 
  theory 
  of 
  instinctive 
  behaviour, 
  and 
  it 
  is 
  

   often 
  held 
  by 
  mechanists 
  in 
  the 
  strict 
  sense. 
  It 
  may, 
  how- 
  

   ever, 
  be 
  held 
  by 
  biologists 
  who 
  admit 
  that 
  vital 
  processes 
  

   cannot 
  be 
  adequately 
  re-described 
  in 
  terms 
  of 
  chemistry 
  and 
  

   physics, 
  who 
  are, 
  however, 
  unwilling 
  to 
  admit 
  in 
  instinctive 
  

   behaviour 
  any 
  reality 
  beyond 
  the 
  physiological 
  processes 
  of 
  

   the 
  animal's 
  nervous 
  system. 
  We 
  shall 
  call 
  it, 
  therefore, 
  the 
  

   reflex 
  theory, 
  rather 
  than 
  the 
  mechanistic 
  theory 
  of 
  instinc- 
  

   tive 
  behaviour. 
  

  

  Instinctive 
  behaviour 
  agrees 
  with 
  reflex 
  acts 
  in 
  not 
  re- 
  

   quiring 
  to 
  be 
  learned, 
  in 
  being 
  dependent 
  on 
  hereditary 
  

   nervous 
  predispositions, 
  and 
  in 
  being 
  exhibited 
  approxi- 
  

   mately 
  in 
  the 
  same 
  way 
  by 
  all 
  similar 
  individuals 
  of 
  the 
  

   species. 
  

  

  It 
  differs 
  from 
  reflex 
  acts 
  in 
  being 
  the 
  activity 
  of 
  the 
  

  

  