Synaptation - a missing concept in the science of evolved complexity
The concept of synaptation is introduced to explain a distinct evolutionary origin of selected effects, in which natural selection operates through emergent cross-level interactions within collectives lacking shared inheritance. The traditional framework excludes such origins from the adaptation-exaptation taxonomy. Yet individual organism fitness is often mediated by collective, non-linear interactions within systems that cannot themselves sustain heredity. To address this, multilevel selection (MLS) theory is extended in the form of synaptive MLS, a process through which heterogeneous task groups evolve emergent traits, called synaptations, whose evolutionary origin lies in irreducible, cross-level selective covariance. Synaptive MLS differs from trait-group selection because collective function depends on causal entanglement among heterogenous entities with diverse fates, rather than a common trait that links entities to a shared fate. This framework applies to conspecific divisions of labor, multi-species consortia and holobiont integration, where coordination of distinct roles yields emergent fitness effects. Synaptation recognizes how natural selection can generate novel emergent functions by coordinating adaptive, exaptive, and neutral organism-level traits whose lower-level roles scaffold higher-level selected effects. Synaptation and adaptation define the endpoints of a continuum of selected-effect complexity. Recognition of this continuum extends the Darwinian paradigm to adaptive complexity in systems that fail classical heredity requirements and offers an evolutionary lens for understanding relational phenomena such as eubiosis, dysbiosis, and rebiosis in holobionts. Significance StatementNatural selection is typically understood to require heredity, yet some complex and functionally integrated biological systems in nature lack a mechanism for collective reproduction. This project introduces synaptation, a theoretical framework that recognizes a distinct evolutionary origin of selected effects, in which fitness consequences arise through non-additive, cross-level interactions rather than through collective reproduction. Synaptive multilevel selection explains how functionally integrated traits can originate by natural selection in non-reproducing collectives, bridging molecular, ecological, and social forms of cooperation. By revealing how coordination of lower-level traits can scaffold the emergence of higher-level selected effects, this framework extends the reach of evolutionary theory and offers new insight into the eco-evolutionary dynamics that sustain collective health, stability, and resilience in multi-species systems.