ABSTRACT
In recent times, it has been practical problem solving that has driven the extension of the concept from the individual to the population and beyond. Veterinarians for example are confronted daily with questions of disease in organisms, but they soon recognised that the health of the herd (or population) was itself a legitimate concept (Ribble et al, 1997; Waltner-Toews, 1996). The concept yet extends further, and the writings of Aldo Leopold (1941) foreshadowed the explosive efforts of recent decades to examine the health of largescale ecosystems (Rapport, Gaudet and Calow, 1995).
