The smart fraction theory argues that the fraction of very high IQ individuals in a society is especially important for a society achieving various positive valued outcomes (such as scientific progress, economic development, and government effectiveness).
A related theory is that the fraction of very low IQ individuals in a society (the "non-smart fraction") is especially important for various negative societal outcomes (such as prevalence of crime and sexually transmitted diseases). However, at extremely low IQ levels other effects may occur, such as individuals having trouble performing basic functions, which would also limit the ability to perform, for example, crime. But such a low IQ may instead cause, for example, a need for extensive societal care.
Many characteristics (such as IQ) that are influenced by many factors (like by many genes) will (due to the "central limit theorem") have a "normal distribution" (a "bell curve" distribution). However, a characteristic of this distribution is that group differences will be amplified at the extremes. Thus, group differences will be increasingly more pronounced at extreme values than they are at more average values. As such, only a small average IQ group difference may imply large group differences regarding the smart/non-smart fractions, which are particularly important for society according to the smart fraction theory.
One example is regarding racial IQ differences. Such differences will be more pronounced at extreme values than at more average values.
Another example is regarding dysgenics. A 2010 study stated regarding dysgenic fertility (high IQ individuals having fewer children but ignoring immigration effects) in the United States that "The implications of the present findings for the United States need to be stated clearly: Assuming an indefinite continuation of current fertility patterns, an unchanging environment and a generation time of 28 years, the IQ will decline by about 2.9 points/century as a result of genetic selection. The proportion of highly gifted people with an IQ higher than 130 will decline by 11.5% in one generation and by 37.7% in one century." Thus, the smart fraction, that the smart fraction theory argues is especially important for society, is argued to be reduced at a relatively fast rate in the United States despite only small changes in average group IQ (again, ignoring immigration effects).
Similarly, the immigration of low average IQ immigrant groups may cause disproportionate effects on the for society more important smart/non-smart fractions than on the relatively less important average IQ.
The smart fraction theory may also have implications for IQ differences and societal position differences between men and women. Some recent studies have found small average IQ differences between men and women. However, these differences have been argued to be amplified at extreme values, which is one argued explanation for males being more common than females at many higher level positions in society.
The smart fraction theory only discusses IQ but a similar situation may possibly also apply to other group differences.
- Rindermann, H., Sailer, S., & Thompson, J. (2009). The impact of smart fractions, cognitive ability of politicians and average competence of peoples on social development. Talent Development & Excellence, 1, 3–25.
- Heiner Rindermanna, Oasis Kodila-Tedika, Gregory Christainsen. (2015). Cognitive capital, good governance, and the wealth of nations Intelligence, Volume 51, July–August 2015, Pages 98–108. https://www.sciencedirect.com/science/article/pii/S0160289615000781?np=y
- Meisenberg, Gerhard (2010). "The reproduction of intelligence". Intelligence 38 (2): 220–230. http://dx.doi.org/10.1016/j.intell.2010.01.003
- Helmuth Nyborg, Sex-related differences in general intelligence g, brain size, and social status, Personality and Individual Differences, Volume 39, Issue 3, August 2005, Pages 497-509, ISSN 0191-8869, http://dx.doi.org/10.1016/j.paid.2004.12.011