Goal - I am trying to implement a genetic algorithm to optimise the fitness of a species of creatures in a simulated two-dimensional world. The world contains edible foods, placed at random, and a population of monsters (your basic zombies). I need the algorithm to find behaviours that keep the creatures well fed and not dead.

What i have done -

So i start off by generating a 11x9 2d array in numpy, this is filled with random floats between 0 and 1. I then use np.matmul to go through each row of the array and multiply all of the random weights by all of the percepts (w1+p1*w2+p2....w9+p9) = a1.

This first generation is run and I then evaluate the fitness of each creature using (energy + (time of death * 100)). From this I build a list of creatures who performed above the average fitness. I then take the best of these "elite" creatures and put them back into the next population. For the remaining space I use a crossover function which takes two randomly selected "elite" creatures and mixes their genes. I have tested two different crossover functions one which does a two point crossover on each row and one which takes a row from each parent until the new child has a complete chromosome. My issue is that the creatures just don't really seem to be learning, at 75 turns I will only get 1 survivor every so often.

I am fully aware this might not be enough to go off but I am truly stuck on this and cannot figure out how to get these creatures to learn even though I think I am implementing the correct procedures. Occasionally I will get a 3-4 survivors rather than 1 or 2 but it appears to occur completely randomly, doesn't seem like there is much learning happening.

Below is the main section of code, it includes everything I have done but none of the provided code for the simulation

#!/usr/bin/env python
from cosc343world import Creature, World
import numpy as np
import time
import matplotlib.pyplot as plt
import random
import itertools

# You can change this number to specify how many generations creatures are going to evolve over.
numGenerations = 2000

# You can change this number to specify how many turns there are in the simulation of the world for a given generation.
numTurns = 75

# You can change this number to change the world type.  You have two choices - world 1 or 2 (described in
# the assignment 2 pdf document).

# You can change this number to modify the world size.

# You can set this mode to True to have the same initial conditions for each simulation in each generation - good
# for development, when you want to have some determinism in how the world runs from generation to generation.

# This is a class implementing you creature a.k.a MyCreature.  It extends the basic Creature, which provides the
# basic functionality of the creature for the world simulation.  Your job is to implement the AgentFunction
# that controls creature's behaviour by producing actions in response to percepts.
class MyCreature(Creature):

    # Initialisation function.  This is where your creature
    # should be initialised with a chromosome in a random state.  You need to decide the format of your
    # chromosome and the model that it's going to parametrise.
    # Input: numPercepts - the size of the percepts list that the creature will receive in each turn
    #        numActions - the size of the actions list that the creature must create on each turn
    def __init__(self, numPercepts, numActions):

        # Place your initialisation code here.  Ideally this should set up the creature's chromosome
        # and set it to some random state.
        #self.chromosome = np.random.uniform(0, 10, size=numActions)
        self.chromosome = np.random.rand(11,9)
        self.fitness = 0

        # Do not remove this line at the end - it calls the constructors of the parent class.

    # This is the implementation of the agent function, which will be invoked on every turn of the simulation,
    # giving your creature a chance to perform an action.  You need to implement a model here that takes its parameters
    # from the chromosome and produces a set of actions from the provided percepts.
    # Input: percepts - a list of percepts
    #        numAction - the size of the actions list that needs to be returned
    def AgentFunction(self, percepts, numActions):

        # At the moment the percepts are ignored and the actions is a list of random numbers.  You need to
        # replace this with some model that maps percepts to actions.  The model
        # should be parametrised by the chromosome.

        #actions = np.random.uniform(0, 0, size=numActions)

        actions = np.matmul(self.chromosome, percepts)

        return actions.tolist()

# This function is called after every simulation, passing a list of the old population of creatures, whose fitness
# you need to evaluate and whose chromosomes you can use to create new creatures.
# Input: old_population - list of objects of MyCreature type that participated in the last simulation.  You
#                         can query the state of the creatures by using some built-in methods as well as any methods
#                         you decide to add to MyCreature class.  The length of the list is the size of
#                         the population.  You need to generate a new population of the same size.  Creatures from
#                         old population can be used in the new population - simulation will reset them to their
#                         starting state (not dead, new health, etc.).
# Returns: a list of MyCreature objects of the same length as the old_population.

def selection(old_population, fitnessScore):
    elite_creatures = []
    for individual in old_population:
        if individual.fitness > fitnessScore:

    elite_creatures.sort(key=lambda x: x.fitness, reverse=True)

    return elite_creatures

def crossOver(creature1, creature2):
    child1 = MyCreature(11, 9)
    child2 = MyCreature(11, 9)
    child1_chromosome = []
    child2_chromosome = []

    #print("parent1", creature1.chromosome)
    #print("parent2", creature2.chromosome)

    for row in range(11):
        chromosome1 = creature1.chromosome[row]
        chromosome2 = creature2.chromosome[row]

        index1 = random.randint(1, 9 - 2)
        index2 = random.randint(1, 9 - 2)

        if index2 >= index1:
            index2 += 1
        else:  # Swap the two cx points
            index1, index2 = index2, index1


    child1.chromosome = child1_chromosome
    child2.chromosome = child2_chromosome

    #print("child1", child1_chromosome)

    return(child1, child2)

def crossOverRows(creature1, creature2):
    child = MyCreature(11, 9)

    child_chromosome = np.empty([11,9])

    i = 0

    while i < 11:
        if i != 10:
            child_chromosome[i] = creature1.chromosome[i]
            child_chromosome[i+1] = creature2.chromosome[i+1]
            child_chromosome[i] = creature1.chromosome[i]

        i += 2

    child.chromosome = child_chromosome

    return child

    # print("parent1", creature1.chromosome[:3])
    # print("parent2", creature2.chromosome[:3])
    # print("crossover rows ", child_chromosome[:3])

def newPopulation(old_population):
    global numTurns

    nSurvivors = 0
    avgLifeTime = 0
    fitnessScore = 0
    fitnessScores = []

    # For each individual you can extract the following information left over
    # from the evaluation.  This will allow you to figure out how well an individual did in the
    # simulation of the world: whether the creature is dead or not, how much
    # energy did the creature have a the end of simulation (0 if dead), the tick number
    # indicating the time of creature's death (if dead).  You should use this information to build
    # a fitness function that scores how the individual did in the simulation.
    for individual in old_population:

        # You can read the creature's energy at the end of the simulation - it will be 0 if creature is dead.
        energy = individual.getEnergy()

        # This method tells you if the creature died during the simulation
        dead = individual.isDead()

        # If the creature is dead, you can get its time of death (in units of turns)
        if dead:
            timeOfDeath = individual.timeOfDeath()
            avgLifeTime += timeOfDeath
            nSurvivors += 1
            avgLifeTime += numTurns

        if individual.isDead() == False:
            timeOfDeath = numTurns

        individual.fitness = energy + (timeOfDeath * 100)
        fitnessScore += individual.fitness
        #print("fitnessscore", individual.fitness, "energy", energy, "time of death", timeOfDeath, "is dead", individual.isDead())

    fitnessScore = fitnessScore / len(old_population)

    eliteCreatures = selection(old_population, fitnessScore)


    newSet = []

    for i in range(int(len(eliteCreatures)/2)):
        if eliteCreatures[i].isDead() == False:

    print(len(newSet), " elites added to pop")

    remainingRequired = w.maxNumCreatures() - len(newSet)

    i = 1

    while i in range(int(remainingRequired)):
        newSet.append(crossOver(eliteCreatures[i], eliteCreatures[i-1])[0])
        if i >= (len(eliteCreatures)-2):
            i = 1
        i += 1

        remainingRequired = w.maxNumCreatures() - len(newSet)

    # Here are some statistics, which you may or may not find useful
    avgLifeTime = float(avgLifeTime)/float(len(population))
    print("Simulation stats:")
    print("  Survivors    : %d out of %d" % (nSurvivors, len(population)))
    print("  Average Fitness Score :", fitnessScore)
    print("  Avg life time: %.1f turns" % avgLifeTime)

    # The information gathered above should allow you to build a fitness function that evaluates fitness of
    # every creature.  You should show the average fitness, but also use the fitness for selecting parents and
    # spawning then new creatures.

    # Based on the fitness you should select individuals for reproduction and create a
    # new population.  At the moment this is not done, and the same population with the same number
    # of individuals is returned for the next generation.

    new_population = newSet

    return new_population

# Pygame window sometime doesn't spawn unless Matplotlib figure is not created, so best to keep the following two
# calls here.  You might also want to use matplotlib for plotting average fitness over generations.

# Create the world.  The worldType specifies the type of world to use (there are two types to chose from);
# gridSize specifies the size of the world, repeatable parameter allows you to run the simulation in exactly same way.
w = World(worldType=worldType, gridSize=gridSize, repeatable=repeatableMode)

#Get the number of creatures in the world
numCreatures = w.maxNumCreatures()

#Get the number of creature percepts
numCreaturePercepts = w.numCreaturePercepts()

#Get the number of creature actions
numCreatureActions = w.numCreatureActions()

# Create a list of initial creatures - instantiations of the MyCreature class that you implemented
population = list()
for i in range(numCreatures):
   c = MyCreature(numCreaturePercepts, numCreatureActions)

# Pass the first population to the world simulator

# Runs the simulation to evaluate the first population

# Show the visualisation of the initial creature behaviour (you can change the speed of the animation to 'slow',
# 'normal' or 'fast')
w.show_simulation(titleStr='Initial population', speed='normal')

for i in range(numGenerations):
    print("\nGeneration %d:" % (i+1))

    # Create a new population from the old one
    population = newPopulation(population)

    # Pass the new population to the world simulator

    # Run the simulation again to evaluate the next population

    # Show the visualisation of the final generation (you can change the speed of the animation to 'slow', 'normal' or
    # 'fast')
    if i==numGenerations-1:
        w.show_simulation(titleStr='Final population', speed='normal')
  • $\begingroup$ Welcome to AI--you've certainly put a great deal of effort on this! (I took the liberty of adding the "game-ai" tag, because this constitutes a form of game.) I especially appreciate the extensive commenting in your code. $\endgroup$
    – DukeZhou
    Commented May 11, 2018 at 13:32
  • 1
    $\begingroup$ Is it difficult to answer if you do not describe btter with are the rules of the world. In the provided code, important parts are not present, in particular agent behavior, energy evolution, ... . $\endgroup$ Commented May 12, 2018 at 10:18

1 Answer 1


I think there are two problems with your approach.

First, your genetic algorithm contains crossover, but no mutations at all. In a GA, crossover causes convergence, while mutation is the only "exploration" operation. This means your creatures are stuck with whatever genes were present in their small initial population, and, even with modest selection pressures, they will rapidly converge to all being identical to each other. A common way to add mutation is to assign a random value to each location in each child's genome with a small probability (say, 0.01 * 1/number_of_genes). Some researchers prefer higher values. I'm not sure it's been definitely shown which is better, but it likely depends on your problem.

Second, throwing away agents that died might not be the best selection mechanism. You might get more interesting behaviours if you tied reproduction to something else (e.g. eating a lot of food while you were alive). Right now, your fitness function is probably incentivizing agents to hide in a corner and not do anything, since this maximizes the chance they survive to the end of the simulation.

Hope this helps a bit.


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