The power of the weak: When altruism is the equilibrium.

A rational economic analysis complements Grossmann's fearful ape hypothesis. Two examples of mixed-motive games with strong inter-dependence (i.e., weak chirping nestling, boxed pigs) demonstrate that signaling weakness is a dominant strategy. Weakness elicits cooperative, caring response, comprising the equilibrium of the game. In extensive form, a reliable reputation of weakness elicits caring as a sequential equilibrium.