A term with a wide array of different meanings. Stated simply, it is the actions and activities assigned to, expected of, or required of an organism or group or relationship. In mathematics, it is used whenever some quantity (viz., the dependent variable) is regarded as being determined by other quantities (viz., the independent variable). In biology, broadly defined, it is taken to mean the natural or special type of action that is proper for any specialized organ (e.g., the heart) or part (e.g., the sinoatrial node) that has been acted upon by natural selection and which is thus synonymous with survival value. The problem with this definition is that when we turn to other organic structures (e.g., the hand), they take on a variety of functions, natural or otherwise. The term ‘neural function’ is used to designate circumscribed behaviors assumed to have structural correlates in the nervous system and which in turn promote the integrity of these structures through their actions. As with the pathways linking genotype and phenotype, this assumption raises unanswered questions about those between a specific function and a particular neural structure, especially in the context of ontogenetic development.
See Convergent evolution, Evolutionary emergence, Genotype and phenotype, Ontogenetic development, Organism, Structure, Structure-function relationships, Theory of natural selection