Siblings, strangers, and the surge of altruism

Oded Stark*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


We demonstrate how altruism can surge in a population of nonaltruists. We assume that each individual plays a one-shot prisoner's dilemma game with his or her sibling, or with a stranger, and that the probability that an individual survives to reproduce is proportional to his or her payoff in this game. We model the formation of couples and the rule of imitation of parents and of nonparents. We then ask what happens to the proportion of altruists in the population. We specify a case where the unique and stable equilibrium is one in which the entire population will consist of altruists.

Original languageEnglish
Pages (from-to)135-142
Number of pages8
JournalEconomics Letters
Issue number2
StatePublished - Nov 1999
Externally publishedYes


  • A13
  • D64
  • Evolution of altruism
  • One-shot prisoner's dilemma game
  • Siblings and strangers


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