Gene and Organism

Webster's dictionary gives as its second definition of "organism" (the first being merely as a synonym of organic structure or organization) "an individual constituted to carry on the activities of life by means of parts or organs, more or less separate in function but mutually dependent; any living being; any animal or plant." The phrase "activities of life' may be taken to include primarily all physiological processes and behavior tending toward persistence of the individual, but with "persistence" qualified of course by growth, development and adaptive change. Secondarily it includes the reproductive processes that tend toward persistence and multiplication of the type. The mutual dependence of parts stressed in the definition is exhibited to widely varying extents among plants and animals, In some of the lower forms, there is little more than physical continuity among parts that carry on their activities almost independently. In some thallophytes and all higher plants, a closer integration is brought about by vascular bundles. Most animals are integrated not only by physical continuity and a common vascular system but by a nervous system: a loose nerve net in lower forms, a central nervous system in higher ones. About a century and a half ago it began to be recognized that all but certain microscopic plants and animals are composed of somewhat similar microscopic bodies, cells, each of which carries on its life processes largely by and for itself. It gradually became clear that cells arise only by division of preexistent cells. The concept that cells are organisms in the strictest sense has been borne out by studies of tissue cultures. The familiar organisms are thus recognized to be also colonies of organisms.