Predator inspection Divided We Stand: The Evolution of Altruism Karthik Panchanathan buddha@ucla.edu Territorial defense Hunting Grooming Altruism: Costly behavior that helps others Food sharing Warfare Eusociality Allo-parenting Darwin 101 Natural Selection is the evolutionary mechanism by which organisms adapt to their environment Darwin s postulates are the necessary conditions for natural selection to occur: 1. There must be competition for access to resources, mates, etc. 2. There must be variation in the ability to survive and reproduce 3. This variation must be heritable Time 1 Time 10 Time 20 The Paradox of Altruism The logic of adaptation of by natural selection applies to behavior as well as morphology Because altruism entails a cost to the actor, there is a social dilemma: Helping maximizes the fitness/welfare of the group (actor + recipient), if the benefit exceeds the cost Not helping maximizes the fitness/welfare of the actor If natural selection is the survival of the fittest how can altruism evolve, when selfinterested behavior is the best option?
Darwin s Dilemma I will not here enter on these several cases, but will confine myself to one special difficulty, which at first appeared to me insuperable, and actually fatal to the whole theory. I allude to the neuters or sterile females in insect communities: for these neuters often differ widely in instinct and in structure from both the males and fertile females, and yet, from being sterile, they cannot propagate their kind. (Darwin, 1859) What do we mean by altruism? Psychological Altruism: In psychology, altruism often refers to the motivation to help others at a personal cost. Behavioral Altruism: In economics, altruism refers to behavior that increases the welfare of another individual at cost to the actor, as measured within a single interaction bout. Evolutionary Altruism: In biology, altruism refers to behavior that increases the fitness of another organism and reduces the fitness of the actor, measured across the life span. Psychological Altruism Behavioral Altruism...mutual cooperation and the punishment of defectors activate reward-related neural circuits, suggesting that evolution has endowed humans with...mechanisms that render altruistic behavior psychologically rewarding. Fehr and Rockenbach, 2004 Many economists and evolutionists believe that altruism emerges from selfish motives (e.g., reciprocity, reputation) No hint of genuine charity ameliorates our vision of society, once sentimentalism has been laid aside. What passes for cooperation turns out to be a mixture of opportunism and exploitation Scratch an altruist, and watch a hypocrite bleed. (Ghiselin, 1974)
Let s play a game Suppose I give one person (the proposer) $10 and ask her how she would like to allocate this money between herself and another person, in another room, whom she will never meet. The other person (the responder) can accept the proposed division, and both go home with some money; or, he can reject the division, and both go home with nothing. If you were the proposer, what would you offer? If you were the responder, what is the minimum acceptable offer? Experimental Economics Designed to test the selfishness axiom Participants make real choices involving substantial sums of money Participants can benefit others at a person cost Experiments are one-shot and anonymous, so reciprocity or reputation cannot motivate behavior The experiment you participated in is the Ultimatum Game, which models the last stage of a negotiation take it or leave it! Ultimatum Game If people were self-interested: People aren t self-interested: Responders should accept any non-zero offer Anticipating this, proposers should offer $1 100s studies in US, Europe, and Asia Most proposers offer half of the money Offers less than 20% are usually rejected Offers are rational given pattern of rejections Low computer-driven offers are accepted Cross-Cultural Experiments
Machiguenga Au and Gnau Tend to make lower offers Tend to accept lower offers Social interactions mainly within nuclear families Economics students often behave the same way! Large offers are often rejected! Extreme generosity used to shame people We sometimes do this with elaborate gift giving, especially during the Holidays Third Party Punishment Game Measures the willingness to pay to enforce the fairness norm Allocator decides how much of his $10 endowment he wants to transfer to the recipient The recipient must accept whatever is offered; there is no possibility to reject After the allocation, an observer can subtract $3 from the allocator at a personal cost of $1 Self-interested observers should not pay to punish unfair allocations People do pay to punish Percentage of Observers who punish Recipients beliefs Observers decisions 100 80 60 40 20 0 0 1 2 3 4 5 Allocator s transfer to Recipient Fehr and Fischbacher, 2004
Behavioral Altruism The evidence forces us to reconsider our model of human behavior humans have other-regarding preferences in addition to self-regarding preferences Other-regarding preferences includes anti-social or spiteful behavior, in addition to prosocial or altruistic behavior Evolutionary Altruism We build mathematical models to study the evolutionary process Models put verbal logic to a more precise test a fancy way of evaluating if p then q Experiments ask what the world is actually like, whereas models are thinking aids. Models are necessarily simplified caricatures of the real world, which, like maps, are useful if they are built for specific purposes, only including the crucial details and discarding the rest. Darwin s Explanation (of us) Group Selection Within-Group Selection It must not be forgotten that although a high standard of morality gives but a slight or no advantage to each individual man and his children over the other men of the same tribe, yet that an advancement in the standard of morality and in increase in the number of well-endowed men will certainly give an immense advantage to one tribe over another. There can be no doubt that a tribe including many members who, from possessing in a high degree the spirit of patriotism, fidelity, obedience, courage, and sympathy, were always ready to give aid to each other and to sacrifice themselves for the common good, would be victorious over other tribes; and this would be natural selection. (Darwin 1871) Fitness Altruists Cheats 0 0.25 0.50 0.75 1 Frequency of altruists Social dilemma: Helping maximizes the fitness of the group Not helping maximizes the fitness of the actor 0 time 20
Group Selection Between-Group Selection Within-Group Selection Between-Group Selection Altruists Cheats Fitness 0 0 0 0 0.25 0.50 0.75 1 Frequency of altruists time 20 time 20 time 20 Social dilemma: Helping maximizes the fitness of the group Not helping maximizes the fitness of the actor Pecking Order Artificial group selection on chickens resulted in reduced cannibalism and flightiness, increased life span and productivity Does Group Selection Explain Altruism in Nature? The Price Equation is a mathematical model that captures the tension between within- and between-group selection So, which level of selection wins? Darwin s postulates: There must be competition... There must be variation... This variation must be heritable
Group Selection Forces of Evolution - Natural Selection - Mutation - Migration - Genetic Drift - Non-Random Mating time 2 time 3 time 4 Migration minimizes between-group variation and maximizes withingroup variation Without variation, selection cannot operate between-groups Group Selection So, when trying to understand altruism, one normally look for individual-level mechanisms time 2 time 3 time 4 Evolutionary Explanations of Altruism Kin Selection Reciprocity Social Control Cultural Group Selection Kin Selection Selection can favor genes that promote the fitness of relatives and lower the fitness of the bearer, because relatives carry the same genes Direct fitness = the fitness of the actor Indirect fitness = the fitness of the recipient Inclusive fitness = direct fitness + (indirect fitness * relatedness) Selection maximizes inclusive fitness, not direct fitness William Hamilton
Reciprocity You scratch my back, I ll scratch yours. Cooperation can evolve if: Organisms interact many times Organisms can recognize one another Organisms can act contingently Tit For Tat: Start out cooperating and then match your partner, cooperation for cooperation, defection for defection Robert Trivers Social Control Costly help is self-interested if there are sanctions to not helping, provided the cost of being sanctioned exceeds the cost of helping Reputation Morality Punishment Thomas Hobbes Cultural Group Selection Cultural evolution analogous to genetic evolution The transmission of cultural information is very different than genetic information If cultural transmission can maintain variation between groups, then selection can act on groups, favoring altruism Rob Boyd Cultural Group Selection Migration doesn t eliminate betweengroup cultural variation Norms for withingroup altruism are favored by cultural group selection Baldwin Effect: Subsequent selection domesticates selfish genes time 2 time 3 time 4
Assortment Transforms the Dilemma Altruism can evolve when altruists assort amongst themselves The previously discussed mechanisms generate assortment Darwin s postulates: 1. There must be competition... 2. There must be variation... 3. This variation must be heritable Multi-Level Selection: Cooperation and competition are two sides of the same coin. Cooperation at one level, implied competition at a higher level. No Assortment Full Assortment Man and Beast Animals Humans Kin Selection!! Reciprocity?! Social Control! Cultural Group Selection! It s a Life Full of Wonder Want to know more? Probably all organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed. There is grandeur in this view of life that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being evolved. (Darwin, 1859) Richard Dawkins The Selfish Gene Maynard Smith and Eors Szathmary The Origins of Life Matt Ridley The Origins of Virtue