We propose that what makes an organism is nearly complete cooperation, with strong control of intraorganism conflicts, and no affiliations above the level of the organism as unified as those at the organism level. Organisms can be made up of like units, which we call fraternal organisms, or different units, making them egalitarian organisms. Previous definitions have concentrated on the factors that favor high cooperation and low conflict, or on the adapted outcomes of organismality. Our approach brings these definitions together, conceptually unifying our understanding of organismality. Although the organism is a concerted cluster of adaptations, nearly all directed toward the same end, some conflict may remain. To understand such conflict, we extend Leigh's metaphor of the parliament of genes to include parties with different interests and committees that work on particular tasks.

Original languageEnglish
Pages (from-to)605-616
Number of pages12
Issue number3
StatePublished - Mar 2010


  • Individuality
  • Major transitions
  • Multicellularity
  • Organism
  • Superorganism
  • Symbiosis


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