Heritability of IQ

Research on the heritability of IQ inquires into the degree of variation in IQ within a <a href="/facts/Population/ArxshNuB">population</a> that is due to <a href="/facts/Genetic_variation/f2wzYLbI">genetic variation</a> between individuals in that population. There has been significant controversy in the academic community about the heritability of IQ since research on the issue began in the late nineteenth century. <a href="/facts/Intelligence/pRmAeRsw">Intelligence</a> in the normal range is a <a href="/facts/Quantitative_trait_locus/ztEdNEJg">polygenic trait</a>, meaning that it is influenced by more than one gene, and in the case of intelligence at least 500 genes. Further, explaining the similarity in IQ of closely related persons requires careful study because environmental factors may be correlated with genetic factors. Outside the normal range, certain single gene <a href="/facts/Genetic_disorder/hFqt2NLn">genetic disorders</a>, such as <a href="/facts/Phenylketonuria/0EzHHs3v">phenylketonuria</a>, can negatively affect intelligence. 
Early <a href="/facts/Twin_study/J1ykuTtW">twin studies</a> of adult individuals have found a heritability of IQ between 57% and 73%, with some recent studies showing heritability for IQ as high as 80%. IQ goes from being weakly correlated with genetics for children, to being strongly correlated with genetics for late teens and adults. The heritability of IQ increases with the child's age and reaches a plateau at 14–16 years old, continuing at that level well into adulthood. However, poor prenatal environment, malnutrition and disease are known to have lifelong deleterious effects. Estimates in the academic research of the heritability of IQ have varied from below 0.5 to a high of 0.8 (where 1.0 indicates that monozygotic twins have no variance in IQ and 0 indicates that their IQs are completely uncorrelated). Eric Turkheimer and colleagues (2003) found that for children of low socioeconomic status heritability of IQ falls almost to zero. These results have been challenged by other researchers. IQ heritability increases during early childhood, but it is unclear whether it stabilizes thereafter. A 1996 statement by the <a href="/facts/American_Psychological_Association/907fEfuc">American Psychological Association</a> gave about 0.45 for children and about .75 during and after <a href="/facts/Adolescence/XUkTHFyd">adolescence</a>. A 2004 <a href="/facts/Meta-analysis/IcfChd8z">meta-analysis</a> of reports in Current Directions in Psychological Science gave an overall estimate of around 0.85 for 18-year-olds and older. The general figure for heritability of IQ is about 0.5 across multiple studies in varying populations. 
Although IQ differences between individuals have been shown to have a large hereditary component, it does not follow that disparities in IQ between groups have a genetic basis. The scientific consensus is that genetics does not explain <a href="/facts/Race_and_intelligence/MhE2V3sm">average differences in IQ test performance between racial groups.</a>

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Heritability of IQ