breed [homebodies homebody]
breed [hellraisers hellraiser]

turtles-own 
  [speed]  ;; hellraisers move faster than homebodies  

to setup
  clear-all
  create-homebodies (initial-total-population * (100 - initial-percentage-hellraisers) / 100)
    [become-homebody]
  create-hellraisers (initial-total-population * initial-percentage-hellraisers / 100)
    [become-hellraiser]
  ask turtles 
    [setxy random-xcor random-ycor]
end

to go
  repeat 6 ;; for that smoooth animation we like
    [ask turtles
      [forward (0.167 * speed)
       right 6]
       display ] 
  ask turtles [get-older
               reproduce]
  ask homebodies [party] ;; you don't have to ask the hellraisers ;-)
  plot-populations
  tick
end

to become-homebody
  set color brown
  set speed homebody-speed
end

to become-hellraiser
  set color magenta
  set speed homebody-speed * hellraising-speed-factor
end

to get-older
  if random 100 = 0 [die] ;; accidents happen
end

to party
  if any? hellraisers-here
     and random-normal 0.5 0.2 < susceptibility
     [hatch-hellraisers 1 [become-hellraiser]
      die] ;; can't change breeds at runtime
end

to reproduce 
  if count turtles < 1000 ;; global population cap
     and any? other turtles-here ;; requires a partner on the same patch
     and count turtles-here < crowding-tolerance  ;; but not too many
     and random-normal 0.5 0.2
         < ifelse-value is-hellraiser? self
             [hellraiser-fertility / 10] ;; ten reproduction opportunities per average lifetime
             [homebody-fertility / 10]   ;; (just a guess)
    [ifelse random 2 = 0 ;; uh, what's my sex?
       [hatch 1 [be-born]] ;; i'm a mom!
       [ask one-of other turtles-here ;; i'm a dad!
         [hatch 1 [be-born]]]]
end

to be-born
  set heading (random 360) 
  forward 2 * speed ;; get a little room
end

to plot-populations
  set-current-plot-pen "Homebodies"
  plot count homebodies
  set-current-plot-pen "Hellraisers"
  plot count hellraisers
end

to segregate
  let proportion (count hellraisers / count turtles)
  move-to patch (ifelse-value is-hellraiser? self
                   [proportion  * [pxcor] of patch-here]
                   [world-width - (1 - proportion) * [pxcor] of patch-here])
                ([pycor] of patch-here)
end
@#$#@#$#@
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SLIDER
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TEXTBOX
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.. of homebodies to turning into hellraisers, should they come into contact with one.
11
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TEXTBOX
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.. per agent per average lifetime
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SLIDER
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@#$#@#$#@
WHAT IS IT?
-----------
This is an extremely simplified model of the influence of cultural or "memetic" trait transfer upon population dynamics, roughly corresponding to that first articulated in the book _Culture and the Evolutionary Process_ by Robert Boyd and Peter J. Richerson (1988), and put forward as a "paradigmatic example in memetics" by Derek Gatherer in the Journal of Memetics (2005). Rather than using an abstract recursive procedure involving the population proportions, however, this model uses individual interacting agents in a space. The spatial dynamics may be of interest: in particular, the formation of population source clusters under some conditions was a little surprising to me.

HOW IT WORKS
------------
All agents move around in ten-step circles of size determined by their speed, and have hundred-step average lifetimes. They reproduce sexually at a rate determined by their fertility parameter when they are on the same patch as another agent, only when the global population cap and the local crowding tolerance permit. By sexual reproduction, I mean that either the agent or their randomly-selected partner makes a new agent the same type as the parent.

Homebodies are the brown turtles. They move slower and reproduce more.
Hellraisers are the magenta ones. They move faster, and reproduce less; however they are capable of turning homebodies into hellraisers, to the degree that the former are susceptible.

I've tried to parameterize as much of the model as seemed reasonable so that you can tweak it while it's running, but there are a few hard-coded constants to play with in the procedures, if you're interested.

POSSIBLE EXTENSIONS
-------------------
This isn't supposed to be a realistic model of any particular social phenomenon, but if one would like to get ones hands dirty, there are some very basic things to consider which aren't in the model, such as age, local resources, spatial barriers... plus, there might be more than two kinds of people (or traits, or both) in the world, and all sorts of interactions between traits both inherited and learned might be important. For that matter, there might even (hypothetically) be more kinds of interactions between people than just breeding and partying. If one wants to do science and not just goof off like the present author, then for heaven's sake follow Gatherer's advice and pick a subject where there's some good data against which one might verify the model.


DUE CREDIT
----------
Thanks to the Systems Science school at Portland State University for the Models in 
Science undergraduate course which provided the impetus to make such a thing. I, Max OrHai, hereby kick this program out into the public domain. Go get a job!

Gatherer, D. (2005). Finding a Niche for Memetics in the 21st Century.
Journal of Memetics - Evolutionary Models of Information Transmission, 6.
http://cfpm.org/jom-emit/2005/vol9/gatherer_d.html

Boyd, R. and Richerson, P. J. (1985). Culture and the evolutionary process.
Chicago: The University of Chicago Press

NetLogo is of course Copyright 2002 Uri Wilensky. 'All rights reserved', says he.

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NetLogo 4.1.1
@#$#@#$#@
setup
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[
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  ask bugs [ set-color move-bugs]
  tick
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]
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