to setup clear-output setup-experiment end to setup-experiment clear-patches clear-turtles clear-all-plots clear-ticks create-turtles number [ set color 5 + (random colors) * 10 if color = turquoise ;; turquoise (75) is too similar to another color [ set color magenta ] ;; so use magenta (125) instead setxy random-xcor random-ycor ] reset-ticks end to go if variance [color] of turtles = 0 [ stop ] ask turtles [ rt random 50 lt random 50 fd 0.1 ;; This was originally 1, CCM set it to 0.1 to slow things down ] birth death tick end ;; Get the string (name) of a color to-report translate-color [num] if num = 5 [report "grey"] if num = 15 [report "red"] if num = 25 [report "orange"] if num = 35 [report "brown"] if num = 45 [report "yellow"] if num = 55 [report "green"] if num = 65 [report "lime"] if num = 75 [report "tuquoise"] if num = 85 [report "cyan"] if num = 95 [report "sky"] if num = 105 [report "blue"] if num = 115 [report "violet"] if num = 125 [report "magenta"] ifelse num = 135 [ report "pink" ] [ report "unknown color" ] end ;; to enable many repetitions with same settings to go-experiment go if variance [color] of turtles = 0 [ let fixed-color [color] of one-of turtles set fixed-color translate-color fixed-color output-print (word fixed-color " went to fixation after " ticks " generations") setup-experiment ] end ;; turtles hatch between 0 and 4 babies to birth ask turtles [ hatch random 5 [ fd 0.1 ] ] ;; This was originally 1, CCM set it to 0.1 to slow things down end ;; if the overall population is greater than the original number, ;; randomly kill turtles to keep population roughly constant to death let total-turtles count turtles ask turtles [ if random total-turtles > number [ die ] ] end ; Copyright 1997 Uri Wilensky. ; See Info tab for full copyright and license. @#$#@#$#@ GRAPHICS-WINDOW 320 10 733 424 -1 -1 9.0 1 10 1 1 1 0 1 1 1 -22 22 -22 22 1 1 1 ticks 30.0 BUTTON 98 32 172 65 go go T 1 T OBSERVER NIL NIL NIL NIL 0 BUTTON 12 32 87 65 setup setup NIL 1 T OBSERVER NIL NIL NIL NIL 1 SLIDER 28 77 176 110 colors colors 2 10 2.0 1 1 NIL HORIZONTAL SLIDER 28 114 189 147 number number 10 1000 130.0 10 1 NIL HORIZONTAL PLOT 4 162 317 416 Turtle Populations Time Number 0.0 50.0 0.0 50.0 true false "set-plot-y-range 0 count turtles" "" PENS "color5" 1.0 0 -7500403 true "" "plot count turtles with [color = 5]" "color15" 1.0 0 -2674135 true "" "plot count turtles with [color = 15]" "color25" 1.0 0 -955883 true "" "plot count turtles with [color = 25]" "color35" 1.0 0 -6459832 true "" "plot count turtles with [color = 35]" "color45" 1.0 0 -1184463 true "" "plot count turtles with [color = 45]" "color55" 1.0 0 -10899396 true "" "plot count turtles with [color = 55]" "color65" 1.0 0 -13840069 true "" "plot count turtles with [color = 65]" "color125" 1.0 0 -5825686 true "" "plot count turtles with [color = 75]" "color85" 1.0 0 -11221820 true "" "plot count turtles with [color = 85]" "color95" 1.0 0 -13791810 true "" "plot count turtles with [color = 95]" MONITOR 220 75 306 120 Total Turtles count turtles 0 1 11 BUTTON 181 32 312 65 run-experiment go-experiment T 1 T OBSERVER NIL NIL NIL NIL 1 OUTPUT 318 436 734 602 12 @#$#@#$#@ ## WHAT IS IT? This model is an example of genetic drift. It shows what happens when competing breeds of (asexual) organisms ("turtles"), each reproduce with equal likelihood on each turn. That is, neither breed has a selective advantage. ## HOW IT WORKS The model starts with a random distribution of colored turtles. They move by wiggling randomly across the world. Each turn, a turtle produces between 0 and 4 offspring. If the total number of turtles is greater than the original number, then turtles are randomly killed until the original number is restored. ## HOW TO USE IT The "setup" button initializes the model. The "go" button runs the model. Use the "colors" slider to select the number of competing colors. The "number" slider sets the initial number of turtles. ## THINGS TO DO Set the initial number of colors to “2”, and set the initial number of turtles to “100”. What do you observe? How many generations did it take for one color to go extinct? Run the model under the same conditions at least 5 times. Record which breed went to fixation and how many time steps it took to get to fixation. Is there any evidence to assume that one color is less “fit” than another? Did one color go to fixation more frequently than another? Now adjust the model to begin with a population of 200. Run it at least 5 times again, recording the color that went to fixation and the time step when it reached fixation. How long, on average did a color take to reach fixation with a population of 200? Now set the population to 1,000 and run the model. Look at the size of the jumps in allele frequency from one generation (tick) to the next. How does it compare to the size of the jumps when there were only 100 organisms? (go back and run it with 100 if you need to) Now, adjust the model to have 10 colors, with a beginning population of 200. What trends do you notice as you run the model? How many colors survived to 50 generations? 100? 200? How many generations did it take for one color to reach fixation in this run, as compared to the run with only 2 colors? Why is this? If you were to run the model again, would you suspect that the same color would reach fixation? Why? ## THINGS TO NOTICE Notice that often colors can get to quite a high population but still fail to win the race. After enough turns, a color will gain a slight dominance. By statistical advantage, a dominant color becomes more likely to win the entire grid. However, because the process is random, there will usually be a series of dominant colors before one color finally wins. Equally important is the fact that a color can never come back once it dies out. The idea, explained in more detail in Dennett's "Darwin's Dangerous Idea", is that trait drifts can occur without any particular purpose or 'selecting pressure'. ## EXTENDING THE MODEL Carlo Maley tweaked the code to make the organisms move more slowly. The grim reaper in the procedure `death` does a random harvesting of the population to keep it roughly constant. This might be somewhat like a natural environment with a limited food supply. Can you think of other ways to write this procedure? Are the results affected? ## RELATED MODELS * GenDrift P global * GenDrift P local * GenDrift T interact ## HOW TO CITE If you mention this model or the NetLogo software in a publication, we ask that you include the citations below. For the model itself: * Wilensky, U. (1997). NetLogo GenDrift T reproduce model. http://ccl.northwestern.edu/netlogo/models/GenDriftTreproduce. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL. Please cite the NetLogo software as: * Wilensky, U. (1999). NetLogo. http://ccl.northwestern.edu/netlogo/. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL. ## COPYRIGHT AND LICENSE Copyright 1997 Uri Wilensky. ![CC BY-NC-SA 3.0](http://ccl.northwestern.edu/images/creativecommons/byncsa.png) This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License. To view a copy of this license, visit https://creativecommons.org/licenses/by-nc-sa/3.0/ or send a letter to Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA. Commercial licenses are also available. To inquire about commercial licenses, please contact Uri Wilensky at uri@northwestern.edu. This model was created as part of the project: CONNECTED MATHEMATICS: MAKING SENSE OF COMPLEX PHENOMENA THROUGH BUILDING OBJECT-BASED PARALLEL MODELS (OBPML). The project gratefully acknowledges the support of the National Science Foundation (Applications of Advanced Technologies Program) -- grant numbers RED #9552950 and REC #9632612. This model was converted to NetLogo as part of the projects: PARTICIPATORY SIMULATIONS: NETWORK-BASED DESIGN FOR SYSTEMS LEARNING IN CLASSROOMS and/or INTEGRATED SIMULATION AND MODELING ENVIRONMENT. The project gratefully acknowledges the support of the National Science Foundation (REPP & ROLE programs) -- grant numbers REC #9814682 and REC-0126227. Converted from StarLogoT to NetLogo, 2001. @#$#@#$#@ default true 0 Polygon -7500403 true true 150 5 40 250 150 205 260 250 airplane true 0 Polygon -7500403 true true 150 0 135 15 120 60 120 105 15 165 15 195 120 180 135 240 105 270 120 285 150 270 180 285 210 270 165 240 180 180 285 195 285 165 180 105 180 60 165 15 arrow true 0 Polygon -7500403 true true 150 0 0 150 105 150 105 293 195 293 195 150 300 150 box false 0 Polygon -7500403 true true 150 285 285 225 285 75 150 135 Polygon -7500403 true true 150 135 15 75 150 15 285 75 Polygon -7500403 true true 15 75 15 225 150 285 150 135 Line -16777216 false 150 285 150 135 Line -16777216 false 150 135 15 75 Line -16777216 false 150 135 285 75 bug true 0 Circle -7500403 true true 96 182 108 Circle -7500403 true true 110 127 80 Circle -7500403 true true 110 75 80 Line -7500403 true 150 100 80 30 Line -7500403 true 150 100 220 30 butterfly true 0 Polygon -7500403 true true 150 165 209 199 225 225 225 255 195 270 165 255 150 240 Polygon 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