What is "exogeny"

n. 1 Influence by external forces. 2 Growth on the outside or near the surface. 3 (context botany English) A division of woody plants whose stem is formed by successive accretions to the outside of the wood under the bark 4 (context anatomy English) A phase in the life cycle of a hair follicle in which a hair exits the follicle. 5 (context anthropology English) exogamy.

In a variety of contexts, exogeny or exogeneity is the fact of an action or object originating externally. It contrasts with endogeny or endogeneity, the fact of being influenced within a system.

• In an economic model, an exogenous change is one that comes from outside the model and is unexplained by the model. For example, in the simple supply and demand model, a change in consumer tastes or preferences is unexplained by the model and also leads to endogenous changes in demand that lead to changes in the equilibrium price. Similarly, a change in the consumer's income is given outside the model but affects demand. Put another way, an exogenous change involves an alteration of a variable that is autonomous, i.e., unaffected by the workings of the model.
• In linear regression, an exogenous variable is independent of the random error term in the linear model.
• In biology, an exogenous contrast agent in medical imaging for example, is a liquid injected into the patient intravenously that enhances visibility of a pathology, such as a tumor. An exogenous factor is any material that is present and active in an individual organism or living cell but that originated outside that organism, as opposed to an endogenous factor.
  • Exogenous factors in medicine include both pathogens and therapeutics.
  • DNA introduced to cells via transfection or viral infection ( transduction) is an exogenous factor.
  • Carcinogens are exogenous factors.
• In geography, exogenous processes all take place outside the Earth and all the other planets. Weathering, erosion, transportation and sedimentation are the main exogenous processes.
• In attentional psychology, exogenous stimuli are external stimuli without conscious intention. An example of this is attention drawn to a flashing light in the periphery of vision.
• In ludology, the study of games, an exogenous item is anything outside the game itself. Therefore, an item in a massively multiplayer online game would have exogenous value if people were buying it with real world money rather than in-game currency (though its in-game cost would be endogenous).
• In materials science, an exogenous property of a substance is derived from outside or external influences, such as a nano-doped material.
• In philosophy, the origins of existence of self, or the identity of self, emanating from, or sustaining, outside of the natural or influenced realm, is exogenous.