Contagion - A general term for any disease-causing infectious agent spread by direct or indirect contact.⏎
Ecology - A branch of science that deals with the relation of organisms to one another and their physical environment.⏎
Ecosystem - A functional unit that consists of all the living organisms in a particular area, as well as the nonliving, physical components in the environment—such as air, soil, water, and sunlight—with which the organisms interact, and how natural and human-made changes affect these interactions.⏎
Evolution - The change in heritable traits in a population of organisms over successive generations.⏎