Plasticity and Strong Reciprocity

1. Plasticity and Strong Reciprocity Zeke Hindle and Sarah Llanes Evolutionary 452 22 November 2011 http://www.youtube.com/watch?v=gj57rI1_JX8

2. How Learning Affects the Evolution of Strong Reciprocity Juan Pablo Calderon and Roberto Zarama From the Journal of Adaptive Behavior 2006 Volume 14 Pages 211-221

3. Introduction • Definitions of relevant terms Phenotypic plasticity, lifetime adaptations, ontogenic adaptations, and learning are all used interchangeably and mean “changes that an individual undergoes within his/her lifetime and that will not going to be [sic] inherited directly by offspring” Strong Reciprocity defined as the evolved behavior of humans to “cooperate with non-kin, including people that they will never meet again, and punish non-cooperators even at a personal cost”. Ultimatum Game- Two players (one proposer, one responder) where players split the pot if proposal is sufficient to make the responder accept said offer. Homo Economicusdefined as “a self-interested being who will try to maximize his or her own monetary utility.

4. Introduction • Previous Literature The model for the following experiment was largely taken from the ultimatum game model used by Sanchez and Cuesta (2005), with a few variations, namely the agents and genetic algorithms altered to allow for the study of the affects of plasticity on the evolution of strong reciprocity within the game itself.

5. Model • Same model as ultimatum game but nature of participants (agents) and genetic algorithm was altered to allow for plasticity. • Rigid Agents- Genes (specific actions allowed in the course of the game) randomly selected and force said agent to act in a particular way (i.e. not able to change amount proposed or responded to). • Genetic Algorithm- Two agents randomly selected, one with higher fitness (more money) is replicated (offspring) while the other (less relative money) is discarded from the game. • Plastic Agents- Allowed the ability to adapt. Given a certain genome initially but then allowed to adapt by the augmentation of the phenome. Three Types of Plasticity Type 1 Type 2 Type 3 Inherited

6. Results • Scatterplotswere used to determine the relative changes in the given condition over time. • Rigid Agents- show the rational solution predicted by homo economicus meaning the agents proposed very little and accepted almost anything. Solution is not stable (fluctuates around a mean value). • Plastic Agents Type 1- Overall causes the spread of learnt behaviors and on average decreases offer by 20 percent and increased response by 20 percent. Type 2 and 3- As adaptability of agents increases the average offers and acceptance thresholds increase. As number of games before a given agent becomes rigid increases, offers made are more generous and thresholds less strict. • Plasticity as Evolutionary Stable Strategy (Inherited)

7. Discussion and Conclusions • Costs of Plasticity • Stochasticitydefined as learned wrong behavior by inadequate examples. • Time wasting cost due to learning process. • Mistakes inherent to given form of learning. • Benefits of Plasticity -Efficient exploitation of given environment by agent. -Happens within lifetime and not over generations or mutations. -Might be evolutionarily stable. -Increases diversity of behaviors and genetic diversity thereby increasing the level of -cooperation amongst group members of population -Reduces selection pressure and retains a less converged population. -Allows genetically similar population to display diverse behaviors. -Over time, changes overall behavior of population from selfish to altruistic.

8. Critical Review • Pros -The fact that agents have no memory and anonymous to one another reflects the fact that strong reciprocity does not consider others but only the individual. -Aware that learning (plasticity) is not always beneficial and has its drawbacks. -Variety of methods, conditions, and variables allows researchers to see a wide variety of characteristics associated with the affects of plasticity on strong reciprocity. • Cons -Limited amount of generations and simulations lack the realism of the natural world. -Could make more elaborate learning algorithms and characteristics of agents more reflective of reality. -Complexity of models, variables, conditions, diagrams, and charts difficult to explain to the average reader and could be simplified to reach a larger audience.

9. Test Questions • Multiple Choice 1) Sanchez and Cuesta’s Model of evolutionary game theory (2005) predicts the emergence of strong reciprocity based upon selection acting on: a) the individual b) the group c) both a and b 2) Over time plasticity will evolve behaviors that can be described as: a) selfish b) altruistic c) destructive d) both a and b 3) By definition, strong reciprocity takes into account all of the following except: a) cooperation with kin b) cooperation with non-kin c) cooperation with people that will never interact again d) cooperation even at personal cost

10. Test Questions • True/ False 1) Plasticity can be defined as changes that an individual undergoes within his/her lifetime that will be directly inherited by the offspring of said individual. T or F 2) Altruistic punishment is positively correlated with the evolution of plasticity and strong reciprocity. T or F 3) The evolutionary costs of plasticity are higher than the benefits of plasticity that’s why were are all selfish and mean people. T or F

11. THE END!!!!!!!!!!!! Any Questions?!?!?!?