General summary

Abstract

In any mammal or other complex metazoan the functional structure of the tissues is maintained by layer upon layer of homeostatic mechanisms, beginning at the chemical level and extending upwards to the cellular level, the tissue level, the organ level, the organism level, and even to the population level. Within each of these levels the homeostatic mechanism is partitioned into functional units, which respond to perturbations independently of the other parts of the mechanism, and so confer a considerable adaptive flexibility on the whole. Furthermore, the controls within each organizational level interact with those of other levels’ so that the higher level systems, so called, continue to include in their operation all the relevant activities of the lower-order ones’ (Goodwin, 1976). The result is a highly complex and extremely versatile whole.