||This article needs attention from an expert in Genetics. The specific problem is: This article gives too much emphasis on fringe theories pertaining to human intelligence. (June 2014)|
Dysgenics (also known as cacogenics) is the study of factors producing the accumulation and perpetuation of defective or disadvantageous genes and traits in offspring of a particular population or species. Dysgenic mutations have been studied in animals such as the mouse and the fruit fly. The term dysgenics was first used as an antonym of eugenics—the social philosophy of improving human hereditary qualities by social programs and government intervention.
Two models were proposed aiming to explain this trend —— relative high fertility for those with lower g since the Industrial Revolution; mutation accumulation due to relaxed purifying selection against deleterious mutations in modern populations. 
Much of the debate regarding dysgenics has been about a hypothesized decline in human intelligence due to lower fertility of the more intelligent. It is unclear how environmental factors may limit IQ differently in different populations. While there may be a correlation between IQ and fertility, it is unclear whether that would have any effect on intelligence over generations.
Dysgenics for other traits
In 1996, Lynn wrote Dysgenics: Genetic Deterioration in Modern Populations. He identified three main concerns of eugenicists, such as himself: deterioration in health, intelligence and conscientiousness. Lynn argued that natural selection in pre-industrial societies favored traits such as intelligence and character but no longer does so in modern societies.
This book have been favorably reviewed by some reviewers[clarification needed] while some others works by him have been described by some others as distorting and misrepresenting data.[clarification needed]
The word "dysgenic" was first used, as an adjective, about 1915, by David Starr Jordan, describing the dysgenic effect of World War I. Jordan believed that healthy men were as likely to die in modern warfare as anyone else, and that war killed only the physically healthy men of the populace whilst preserving the disabled at home.
Other counter-acting effects
Lynn and Harvey (2008) suggest that designer babies may have an important counter-acting effect in the future. Initially this may be limited to wealthy couples, who may possibly travel abroad for the procedure if prohibited in their own country, and then gradually spread to increasingly larger groups. Alternatively, authoritarian states may decide to impose measures such as a licensing requirement for having a child, which would only be given to persons of a certain minimum intelligence. The Chinese one-child policy is an example of how fertility can be regulated by authoritarian means. Geoffrey Miller claims the one-child policy was implemented to reduce China's population explosion, and "to reduce dysgenic fertility among rural peasants." However, the one-child policy has made longstanding exceptions for rural families so that those families could have 2 children.
Cyril M. Kornbluth's 1951 short story The Marching Morons is an example of dysgenic fiction, describing a man who accidentally ends up in the distant future and discovers that dysgenics has resulted in mass stupidity. Mike Judge's 2006 film Idiocracy has the same premise, with the main character the subject of a military hibernation experiment that goes awry, taking him 500 years into the future. While in the Kornbluth short story, civilization is kept afloat by a small group of dedicated geniuses, their function has been replaced by automated systems in Idiocracy.
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- "cacogenics". Freedictionary.com. Retrieved 2008-06-29.
Cacogenics, the study of the operation of factors that cause degeneration in offspring, especially as applied to factors unique to separate races. Also called dysgenics.
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- Lynn, R. (2008). "Dysgenic fertility for criminal behaviour". Journal of Biosocial Science 27 (4). doi:10.1017/S0021932000023014.
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- Loehlin JC (1999). "Dysgenics: Genetic Deterioration in Modern Populations, reviewed by John C. Loehlin". Annals of the American Academy of Political and Social Science (fee required). JSTOR 00027162.
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- Dysgenics: Genetic deterioration in modern populations: by Richard Lynn. Westport, CT: Praeger, 1996, 238 pp. $59.95., Journal of Social and Evolutionary Systems, Volume 21, Issue 3, 1998, Pages 343-345, ISSN 1061-7361, http://dx.doi.org/10.1016/S1061-7361(98)80008-8 "This could be one of the most important books written in the last fifty years. "
- Leon K (February 1995). "The Bell Curve: Intelligence and Class Structure in American Life". Scientific American 272.
Lynn's distortions and misrepresentations of the data constitute a truly venomous racism, combined with scandalous disregard for scientific objectivity.
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- Oxford English Dictionary
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- Lynn, R.; Harvey, J. (2008). "The decline of the world's IQ". Intelligence 36 (2): 112. doi:10.1016/j.intell.2007.03.004.
- Edge, Chinese Eugenics, http://edge.org/response-detail/23838/
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- Dysgenics online ebook.