green-beard effect

proper noun

A hypothesis in evolutionary biology that explains selective altruism among individuals of a species, involving preferential treatment of individuals with certain characteristics.

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Meanings

proper nounthe green-beard effect
  1. biologyA hypothesis in evolutionary biology that explains selective altruism among individuals of a species, involving preferential treatment of individuals with certain characteristics.

Origin

Proposed by W. D. Hamilton in 1964, from a hypothetical example used in Richard Dawkins' book The Selfish Gene (1976), whereby a person with a green beard acts altruistically towards other people with green beards.

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Cite this entry
APA

green-beard effect. (n.d.). In WatkinsX Dictionary. Retrieved November 3, 2026, from https://dictionary.watkinsx.com/word/green-beard%20effect

MLA

“green-beard effect.” WatkinsX Dictionary, https://dictionary.watkinsx.com/word/green-beard%20effect. Accessed November 3, 2026.

Chicago

WatkinsX Dictionary, s.v. “green-beard effect,” accessed November 3, 2026, https://dictionary.watkinsx.com/word/green-beard%20effect.

Source: green-beard effect on Wiktionary, CC BY-SA 4.0.