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Altruism A Simulated Investigation COM SCI 194 Honors Research Fall 2007 ~ Spring 2008 Alexander Liu and Eric Chang Professor Amit Sahai Why Study Altruism? • First, a definition • Existence in species both animal and human • Impact on human society and culture • Above all, it’s exciting! Previous Works • Haystack model • The evolution of altruism: Game theory …Fletcher & Zwick • Usage of A-life to support evolutionary biology theories • Avida Mathematical Models • Price’s Equation “In other words, for b>a there may be a positive contribution to the average altruism as a result of a group growing due to its high number of altruists and this growth can offset in-group losses, especially if the variance of the in-group altruism is low. In order for this effect to be significant, there must be a spread in the average altruism of the groups.” • Hamilton’s Rule • • • r = the genetic relatedness B = the additional reproductive benefit C = the reproductive cost to the individual of performing the act. Our Scope • Not about morality or conscientious intent… • Origins and reason for persistence • How does a gene that decreases the fitness of the individual get passed on through generations? Approach • Advantages of virtual simulation • Direct and fast • Building our framework: eden.java • Design parameters and requirements • Limitations and caveats Our Own Little eden (.java) • Overall description • The world environment • Food availability and resolution • Reproduction • Genetic variance through succeeding generations Base Experiment • First in our “main line” of experiments • Either completely altruistic or completely selfish • Random movement • Results • Why? Variable Levels • Altruism levels allowed to vary in increments of 0.1 between 0.0 and 1.0 Variable Altruism, averaged trials 700 600 500 400 300 Sharer 200 100 0 0 -100 0.2 0.4 0.6 0.8 1 1.2 Modifications • Food sharing between parent and child organism • Same trait governs two behaviors Variable Altruism, averaged trials 700 600 500 400 Sharer 300 Sharer/Breeder Breeder 200 100 0 0 -100 0.2 0.4 0.6 0.8 1 1.2 Genes, not Numbers • Instead of a sliding scale, behavior is governed by a gene-set • Genes have a chance to turn on or off Geneset-10, five trials 400 350 300 250 200 150 100 50 0 0 -50 2 4 6 8 10 12 Extension and Comparison • Problems with a small gene-set • Effect of increasing the gene-set • Comparison with the previous results 700 600 500 400 sliding 0-10 300 geneset- 10 values geneset- 20 values 200 100 0 0 -100 2 4 6 8 10 12 Back to the Numbers 0-100 • Altruism levels allowed to vary between 0.00 and 1.00 in increments of 0.01 300 250 200 150 100 50 0 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 800 700 600 500 400 food/breeding breeding only 300 200 100 0 0 -100 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Sexually Determined Altruism • Regardless of starting conditions, the distribution always converges to a selfish result Selective Altruism • In previous experiments, there is no clear advantage to being altruistic • Test Condition: altruistic organisms only share with similarly altruistic neighbors Mutation rate: 20% chance of +- 0.1 S elec tive A ltruis m 120 100 Selective Range: 80 60 Shares with altruists +0.05 range S elec tive A ltruis m 40 20 0 1. 0: 0. 89 . ~0 99 : 0. 79 . ~0 89 : 0. 69 . ~0 79 : 0. 59 . ~0 69 : 0. 49 . ~0 59 : 0. 39 . ~0 49 : 0. 29 . ~0 39 : 0. 19 . ~0 29 : 0. 09 . ~0 19 : 0. 00 . ~0 09 : Altruism vs. Selfishness Revisited • Hording Behavior Observed • Population Distribution Snapshot at Equilibrium: Pure Altruistic – – – – – – – – – – 1.0: 0.9: 0.8: 0.7: 0.6: 0.5: 0.4: 0.3: 0.2: 0.1: 0 0 4 2 15 32 59 87 65 97 Pure Selfish 72 86 79 57 67 41 10 0 1 0 • Equilibrium eventually breaks. • Altruists exhibit much more robustness and consistent rebounding Conclusions • Contingent upon several conditions – Conditional altruism – Relatedness and locality • Beginnings- parent/child interaction • Persistence – Altruists do benefit (each other) – Price Equation Distinctions • Differences between altruism in animal species and in human society • The importance of a persistent culture • And transmission of cultural elements • Genetic basis versus expression And… • Final thoughts • A big thank you • Questions?