Replication in selective systems: Multiplicity of carriers, variation of information, iteration of encounters

An analysis of biological selection aimed at deriving a mechanism-independe nt definition removes Hull et al.'s obligatory requirement for replication of the carriers of information, under conditions, such as those obtaining i n the nervous system, where the information content of a carrier can be mod ified without duplication by an amount controlled by the outcome of interac tions with the environment.