ABSTRACT
A striking characteristic of living things is their enonnous diversity of fonn. In size alone, there is variation from the blue whale and the sequoia tree to the smallest bacteria and on into the area where the living and non-living intermingle amongst the viruses and prions. These creatures combine to fonn the complex, dynamic equilibrium that is the ecology of Earth's biosphere, which shows constant slow variation as new creatures evolve and others become extinct. Life's variation in fonn and ecological function is well beyond the capacity of an individual to comprehend in any detail. Biologists have been driven to divide its diversity into comprehensible groups, and to learn how to distinguish these groups.
