The Individual as Evolutionarily Significant Unit of Itself: Toward a Unified Framework

The concept of Evolutionarily Significant Unit (ESU), introduced by Ryder (1986) for conservation genetics, defines populations with distinct evolutionary legacies worthy of preservation. We propose its radical logical extension: every individual organism constitutes, de jure and de facto, an ESU of itself. Drawing from biological individuality theory (Hull, 1980; Godfrey-Smith, 2009), epigenetics, individual selection theory (Williams, 1966; Mayr, 1963), combinatorial genetics, biosemiotics (von Uexküll, 1909), and stochastic developmental biology, we construct a multi-axis demonstration that no two individuals — across any sexually reproducing species, and arguably beyond — share identical biological identity. This irrepeatability is not merely statistical but ontological, evolutionarily consequential, and ethically significant. We argue for a new integrative field: Individual Evolutionary Ontology (IEO).