ertain systems, sacrifice of one hostfacilitates transmission to the next host (i.e. interspecies transmission). Theinclusiveness of the equilibrium model gives it great potential for accuratepredictability of a broad range of parasite-host interactions. CONCLUSIONTraditional assumptions about the factors determining parasitic strategy havebeen largely apocryphal, ignoring contradictory evidence (Esch andFernandez 1993). Equilibrium models synthesize the temporal (i.e.evolutionary) factors and spatial (i.e. transmission) factors characteristic ofparasite-host systems. Time is required to modulate virulence, while spatialfactors such as host density and transmission strategy determine the directionof the modulation. The development of an inclusive, accurate model hassignificance beyond theoretical biology, given the threat to human populationsposed by pathogens such as HIV (Gibbons 1994). Mass extinctions such asthe Cretaceous event may have resulted from parasite-host interaction(Bakker 1986), and sexual reproduction (i.e. recombination of genes duringmeiosis) may have evolved to increase resistance to parasites (Holmes1993). Parasitism constitutes an immense, if not universal, influence on theevolution of life, with far-reaching paleological and phylogenetic implications.A model which synthesizes the key factors determining parasitic virulence andcan predict the entire range of evolutionary outcomes is crucial to our understanding of the history and future of species interaction....
