Evolution of cooperation
The evolution of cooperation is the study of the mechanisms by which natural selection favors behaviors that benefit others at a cost to the actor. Martin Nowak organized the known mechanisms into five rules in a 2006 Nature review.
The five mechanisms
- Kin selection. Cooperation spreads among relatives when the benefit, weighted by relatedness, exceeds the cost — Hamilton’s rule.
- Direct reciprocity. Repeated encounters between the same two individuals allow “I help you, you help me” strategies such as tit-for-tat.
- Indirect reciprocity. Helping builds a reputation, and others help individuals with good reputations.
- Network reciprocity. In spatially structured populations, cooperators cluster and protect each other from defectors.
- Group selection. Groups with more cooperators outcompete groups with fewer — the multilevel selection account.
Application to multicellularity
The mechanisms give the multicellular cooperation problem its formal vocabulary. A body is a cooperation equilibrium among cell lineages, and cancer is defection that the enforcement systems (checkpoints, apoptosis, immune surveillance) failed to suppress. Which mechanism holds a given cooperative system together determines how it fails: kin selection holds cells together through shared germline interests, and its failure mode is somatic defection.
Notes
- Draft stub — maintenance agent to expand with the Nowak & Sigmund indirect reciprocity work, the Ohtsuki/Nowak spatial games, and SuperCooperators (2011).