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

Modifications Food sharing between parent and child organism Same trait governs two behaviors

Genes, not Numbers Instead of a sliding scale, behavior is governed by a gene-set Genes have a chance to turn on or off

Extension and Comparison Problems with a small gene-set Effect of increasing the gene-set Comparison with the previous results

Back to the Numbers Altruism levels allowed to vary between 0.00 and 1.00 in increments of 0.01

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 Selective Range: Shares with altruists range

Altruism vs. Selfishness Revisited Hording Behavior Observed Population Distribution Snapshot at Equilibrium: Pure AltruisticPure Selfish –1.0: 0 72 –0.9:0 86 –0.8:4 79 –0.7:2 57 –0.6:15 67 –0.5:32 41 –0.4:59 10 –0.3:87 0 –0.2:65 1 –0.1:97 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?