ADAPTEDNESS, EVOLUTION AND A HIERARCHICAL CONCEPT OF FITNESS

Fitness is a consequence of the adaptedness of an entity to its environment. The fitness of an evolutionary entity, when the entity is defined by a set of attributes determining how it interacts with its environment, is manifested as persistence of those attributes. Two measures of fitness are presented to explicate this concept: (1) an extensive measure of the persistence of the original set of attributes in the individual entity and its descendants, but corrected for evolution; this includes as a special case fitness as used in population genetics; and, (2) an intensive measure that is independent of the abundance of descendant exemplars. Fitness as conceived here is a function of survival time, degree of evolution, and when applicable, reproductive contribution. The rate of fitness increase of an entity will vary inversely with the degree of evolutionary change experienced by the entity, its descendants, or both through time. Adaptive evolution can increase the length of time that fitness accumulates by increasing the survival of descendants possessing all or some of the ancestral attributes. Reproduction, where possible, can increase the number of descendants. This concept of fitness is simple, unambiguous, coherent, and applicable to entities at any hierarchical level of interest to ecologists and evolutionary biologists. © 1992 Academic Press Limited.