Evolution of Norms

globals[defections turtlecount turtleno punishcount metapunishcount sd mn difft]
turtles-own[points boldness vengefullness seen? punish?]

to setup
  clear-all
  set turtlecount 20
  set defections 0
  addturtles turtlecount 0 0 0
  reset-ticks
end 

to go100
  repeat 100[
   go
  ]
end 

to go

  ask turtles[
    repeat 4[
      set punishcount 0
      set metapunishcount 0

      ;; Chance of being seen
      set seen? random-float 1

      ;; Defect if think you can get away with it
      if seen? < boldness / 7
         [  ;; Choose to defect
           set points points + 3
           set defections defections + 1

          ask other turtles [
            ;; hurt caused by defection
            set points points - 1

              ;; Did they see this?
              if random-float 1 < seen?[
              ;; Yes, they saw it
              set punish? random-float 1
              ;; Are they going to punish?
              ifelse vengefullness / 7 > punish? [
                ;; they also chose to punish
                set punishcount punishcount + 1
                set points points - 2
              ]
              [ ;; They did not punish; Enforce metanorm version?
                if Metanorm[
                  ask other turtles[
                    ;; enforce metanorm?
                    if random-float 1 < seen?[
                       set metapunishcount metapunishcount + 1
                       set points points - 2
                    ]
                  ]
                  set points points - (9 * metapunishcount)
                  set metapunishcount 0
                ]
              ]
            ]

          ]

          ;; Apply punishment to defector
          set points points - (9 * punishcount)
          set punishcount 0

         ]

    ]
  ]

  ;; evolution. Turtles replicate more if successful in strategies
  set sd standard-deviation [points] of turtles
  set mn mean [points] of turtles

  ask turtles[
    ;;show points
    if points >= mn + sd[
      ;; Most successful individuals have 2 offspring
      hatch 2 [
        set points 0
        setxy random 30 random 30
        ]
    ]
    if (points >= mn - sd) and (points < mn + sd) [
      ;; Mean individuals have just one
      hatch 1 [
        set points 0
        setxy random 30 random 30
        ]
      ]
    die
  ]

  ;; even up the numbers to 20
  set difft  turtlecount - count turtles

  ifelse difft < 0[
    repeat difft * -1[
      ask turtle max[who] of turtles [
       die
      ]
    ]
  ][
     addturtles difft 0 0 0
  ]

  ;; mutation
  ask turtles[
    if random-float 1 <= 0.01[
      set boldness random 8
    ]
    if random-float 1 <= 0.01[
      set vengefullness random 8
    ]
  ]

  ;;update-plots

  tick
  set defections 0
end 

to addturtles [num bold venge pts]
  create-turtles num[
    ifelse bold = 0[
      set boldness random 8
    ][
     set boldness bold
    ]
    ifelse venge = 0[
      set vengefullness random 8
    ][
      set vengefullness venge
    ]

    set points pts
    setxy random 30 random 30
    set shape "person"
    set size 3
    set color blue
  ]
end