Evolution of Altruism

• Many social species, including humans, exhibit altruism by sacrificing their own fitness to benefit others.
• Altruism can manifest in various forms, such as alarm calls or group hunting.
• A central question is how a trait that reduces individual fitness could evolve.

"Good of the species": Why it doesn't work

• The idea that altruism evolves for the good of the species is a complex question often analyzed using "evolutionarily stable strategies" (ESS).
• An ESS is a trait that cannot be "invaded" by alternative strategies.
• A gene promoting pure altruism in food-sharing would lead to better survival rates in populations with that gene due to equitable food distribution.
• Populations of pure altruists are vulnerable to invasion by defectors, who do not sacrifice their fitness but benefit from the altruists' sacrifices.
• Defectors gain a fitness advantage, eventually replacing altruists in the population; therefore, the purely altruistic gene is not evolutionarily stable.
• Benefit to the group alone is not a strong selection force because individuals who don't pay the cost will be more successful.

Evolutionarily stable altruism

• Two crucial ideas explain how altruism could be evolutionarily stable: kin selection and reciprocal altruism.
• Kin selection suggests that benefiting relatives can benefit your genes, even at a personal cost.
• Reciprocal altruism means providing aid to others with the expectation of future payback.

Reciprocal altruism

• Robert Trivers proposed reciprocal altruism, where aid is given with the expectation of future reciprocation.
• Reciprocal altruism requires cognitive abilities.
  • Identifying and remembering individuals.
  • Actions.
  • Outcomes.
  • Motives.
• Species must have repeated interactions, suggesting a long-lived species living in close proximity with other members
• The crucial difference between reciprocal and pure altruists is that reciprocal altruists aid conditionally.
• Reciprocal altruists will stop aiding those who refuse to reciprocate.

Conflict between short-term and longer-term benefits: The Prisoner's Dilemma

• Reciprocal altruism demonstrates how cooperation can evolve, but cooperation is not guaranteed.
• The Prisoner's Dilemma illustrates the tension between short-term self-interest and long-term cooperation.
• In the Prisoner's Dilemma, individuals are better off defecting regardless of the other's choice, but mutual cooperation yields the best outcome.
• People frequently cooperate in these dilemmas, achieving a better result than the "rational" choice.
• The issue is how people might be biased to contribute to group welfare.
• The iterated version of the Prisoner's Dilemma allows players to respond to each other's decisions, fostering trust and cooperation.
• "Tit-for-tat" is an evolutionarily stable strategy in the iterated Prisoner's Dilemma.
  • Start with cooperation.
  • Then treat your partner the way they treated you previously.
• "Tit-for-tat" repays cooperation, and punishes defection.
• Defectors are therefore unable to take over the reciprocal altruists.
• Another stable strategy is to always defect, avoiding exploitation but missing out on cooperation.
• Two evolutionarily stable strategies exist: mutual cooperation and defection.