# Unit of Selection > **Machine-Evolution Nexus:** [[articles/Digital Darwinism and the Invisible World of Machine Evolution|Digital Darwinism and the Invisible World of Machine Evolution]] places this node within the history and governance of substrate-independent evolution. **Domain:** Evolution / Philosophy of Biology **Doc Type:** Canonical Wiki Node **Maturity:** Developed ## Definition A unit of selection is an entity at a level of organization whose heritable differences produce differential reproductive success. ## Nexus Context Genes, cells, organisms and groups can become relevant units under different causal conditions. Major transitions alter which units reproduce as integrated wholes. ## Evidence Boundary The unit cannot be chosen rhetorically; it must be inferred from heredity, fitness effects and conflict structure. A platform containing many agents is not automatically a superorganism. ## Relationships [[wiki/Major Evolutionary Transitions|Major Evolutionary Transitions]], [[wiki/Population|Population]], [[wiki/Differential Reproductive Success|Differential Reproductive Success]], [[wiki/Distributed Intelligence|Distributed Intelligence]] ## Sources / Provenance - Lewontin (1970); multilevel-selection literature.