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Lecture

Week 12.pdf

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Department
Psychology
Course Code
PSYCH 2TT3
Professor
Reuven Dukas

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PNB  2XC3   Nov.  26,  2013   Why  are  rituals  common  &  fighting  rare?   • The  old,  unsatisfying  answer:  otherwise,  many  animals  would  be  injured   • Why  is  the  old  answer  insufficient?   o Animals  don’t  care  for  injuries  of  other  males  (it’s  good  for  them)   o B/c  it  isn’t  based  on  a  proper   evolutionary  analysis  of  individual  fitness:  it  assumes  implicitly  group   selection   o Fighting  would  be  common  if  it’s  the  strategy  that  maximizes  fitness     Evolutionary  stable  strategy  (ESS)   • ESS:  a  strategy  that,  if  used  by  almost  all  individuals  in  a  pop,  wi ll  not  ↓  in  frequency  when  new  strategies  arise.   • Initially  developed  to  explain  the  rarity  of  animal  righting,  but   now  is  used  to  understand  social  interactions.   • The  hawk-­‐dove  game  (pg.  490)   o Suppose  that  2  individuals  contest  a  resource  w/  a  fitness  value   V  &  that  they  can  adopt  1  of  2  strategies   o HAWK:  escalate  &  continue  until  injured  or  until  opponent  retreats   o DOVE:  Display  but  retreat  if  opponent  escalates   o Injury  cost  is  C   à  Hawk-­‐hawk  contest  has  an  even  chance  of  gaining  the  resource  ( V)  or  of  injury  (C)  à  Dove-­‐dove  contest   has  an  even  chance  of  graining  resource  ( V)  w/  no  injury   o EX.  1:  V  >  C  (V=4,  C=2)   o EX.  2:  V  <  C  (V=2,  C=4)   o In  both  examples,  dove  isn’t  an  ESS  b/c  a  rare  hawk  strategy  has  a  higher  payoff   against  dove   o When  V>C,  hawk’s  an  ESS  b/c  a  rare  dove  strategy  has  a  lower  payoff  against  hawks   o When  VC  and:   • V/C  if  V
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