Occupations with few or no barriers to entry become crowded, thereby depressing wage levels. Some sectors dominated by women or immigrants display the phenomenon.
English economist John Stuart Mill (1806-1873) and Irish-born economist Francis Edgeworth (1845-1926) both used this model of discrimination in their economic analyses.
Also see: dual labor market theory, labor force participation, occupation segregation, segmented labor market theory
Source:
J S Mill, Principles of Political Economy with Some of Their Applications to Social Philosophy (London, 1848)