the typical hierarchy of interlocking functional systems that supports the life of organisms of that type.Įach detail of this composite portrait is statistically normal within the species, though the portrait may not exactly resemble any species member. For each type a textbook provides a composite portrait of what I will call the species design, i.e. The idealization is of course statistical, not moral or esthetic or normative in any other way. He subject matter of comparative physiology is a series of ideal types of organisms: the frog, the hydra, the earthworm, the starfish, the crocodile, the shark, the rhesus monkey, and so on. Collectively, all such functions constitute the ‘species design’, against which part-tokens are judged normal or abnormal. So the physiological functions of a part-type are its typical causal contributions to individual survival and reproduction in a whole species, or fraction thereof in the case of functions limited to one age (bone growth) or sex (lactation). But physiological function statements are typically made not about individual organisms, but about a class of them. Boorse suggests that, for physiology, the highest-level goals, of the organism as a whole, are individual survival and reproduction. On this account, the physiology of any organism is a hierarchy of goaldirected systems, the goals at each level contributing to those of the next. A physical system has the purely physical, nonintensional, property of being directed to goal G when disposed to adjust its behavior, through some range of environmental variation, in ways needed to achieve G. It views functions as causal contributions to goals of a goal-directed system, as described by Sommerhoff and Nagel. īoorse bases this statistical-functional view of health on a view of biological function sometimes called the cybernetic analysis. Health in a member of the reference class is normal functional ability: the readiness of each internal part to perform all its normal functions on typical occasions with at least typical efficiency.Ī disease is a type of internal state which impairs health, i.e., reduces one or more functional abilities below typical efficiency. Later, however, he expressed doubt about it, so it is best to stick to his simpler account: Boorse's original definition had a special clause to cope with universal environmental injuries. Finally, since many functions, like sweating or blood clotting, are performed only on suitable occasions, what health requires is functional readiness of every part to perform all its normal functions if such occasions arise. In either case, the reference class for statistical normality is a fraction of a species - specifically, an age group of a sex of a species (e.g., 7-9-year-old girls), perhaps further subdivided by race. But Boorse also allows for mere statistical subnormality of function, under some arbitrarily chosen minimum level below the mean. In most disease states, parts at some organizational level - organs, tissues, cells, organelles, genes - totally fail to perform at least one of their species-typical biological functions. What unifies all pathological conditions, says Boorse, is (potential) biological dysfunction of some part or process in an organism.
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