Editing Intelligence quotient (section)

==Genetics and environment==
[[Environment (biophysical)|Environmental]] and [[Heredity|genetic]] factors play a role in determining IQ. Their relative importance has been the subject of much research and debate.<ref>{{citation|title=Continuity of Genetic and Environmental Influences on Cognition across the Life Span: A Meta-Analysis of Longitudinal Twin and Adoption Studies|first1=Elliot M|last1=Tucker-Drob|first2=Daniel A|last2=Briley|journal=Psychological Bulletin|year=2014|volume=140|issue=4|pages=949–979|doi=10.1037/a0035893|pmc=4069230|pmid=24611582}}</ref>

===Heritability===
{{See also|Heritability of IQ|Environment and intelligence}}

The general figure for the [[heritability]] of IQ, according to an [[American Psychological Association]] report, is 0.45 for children, and rises to around 0.75 for late adolescents and adults.{{sfn|Neisser et al.|1995}} Heritability measures for [[G factor (psychometrics)|''g'' factor]] in infancy are as low as 0.2, around 0.4 in middle childhood, and as high as 0.9 in adulthood.<ref name="BouchardWilson2013">{{cite journal |last1=Bouchard |first1=Thomas J. |title=The Wilson Effect: The Increase in Heritability of IQ With Age |journal=Twin Research and Human Genetics |date=7 August 2013 |volume=16 |issue=5 |pages=923–930 |doi=10.1017/thg.2013.54 |pmid=23919982 |s2cid=13747480|doi-access=free }}</ref><ref name="PanizzonVuoksimaa2014">{{cite journal |last1=Panizzon |first1=Matthew S. |last2=Vuoksimaa |first2=Eero |last3=Spoon |first3=Kelly M. |last4=Jacobson |first4=Kristen C. |last5=Lyons |first5=Michael J. |last6=Franz |first6=Carol E. |last7=Xian |first7=Hong |last8=Vasilopoulos |first8=Terrie |last9=Kremen |first9=William S. |date=March 2014 |title=Genetic and environmental influences on general cognitive ability: Is ''g'' a valid latent construct? |journal=Intelligence |volume=43 |pages=65–76 |doi=10.1016/j.intell.2014.01.008 |pmc=4002017 |pmid=24791031}}</ref> One proposed explanation is that people with different genes tend to reinforce the effects of those genes, for example by seeking out different environments.{{sfn|Neisser et al.|1995}}<ref>{{cite journal |display-authors=8 |last1=Huguet |first1=Guillaume |last2=Schramm |first2=Catherine |last3=Douard |first3=Elise |last4=Jiang |first4=Lai |last5=Labbe |first5=Aurélie |last6=Tihy |first6=Frédérique |last7=Mathonnet |first7=Géraldine |last8=Nizard |first8=Sonia |last9=Lemyre |first9=Emmanuelle |last10=Mathieu |first10=Alexandre |last11=Poline |first11=Jean-Baptiste |last12=Loth |first12=Eva |last13=Toro |first13=Roberto |last14=Schumann |first14=Gunter |last15=Conrod |first15=Patricia |last16=Pausova |first16=Zdenka |last17=Greenwood |first17=Celia |last18=Paus |first18=Tomas |last19=Bourgeron |first19=Thomas |last20=Jacquemont |first20=Sébastien |author21=IMAGEN Consortium |title=Measuring and Estimating the Effect Sizes of Copy Number Variants on General Intelligence in Community-Based Samples |journal=JAMA Psychiatry |date=May 2018 |volume=75 |issue=5 |pages=447–457 |doi=10.1001/jamapsychiatry.2018.0039 |pmid=29562078 |pmc=5875373}}</ref>

===Shared family environment===
Family members have aspects of environments in common (for example, characteristics of the home). This shared family environment accounts for 0.25–0.35 of the variation in IQ in childhood. By late adolescence, it is quite low (zero in some studies). The effect for several other psychological traits is similar. These studies have not looked at the effects of extreme environments, such as in abusive families.{{sfn|Neisser et al.|1995}}<ref>{{cite journal |last1=Bouchard |first1=TJ Jr. |title=Genetic and environmental influences on adult intelligence and special mental abilities |journal=Human Biology; an International Record of Research |volume=70 |issue=2 |pages=257–79 |year=1998 |pmid=9549239}}</ref><ref name="Plomin0103">{{cite journal |last1=Plomin |first1=R |last2=Asbury |first2=K |last3=Dunn |first3=J |title=Why are children in the same family so different? Nonshared environment a decade later |journal=Canadian Journal of Psychiatry |volume=46 |issue=3 |pages=225–33 |year=2001 |pmid=11320676|doi=10.1177/070674370104600302 |doi-access=free}}</ref>{{sfn|Harris|2009|p={{page needed|date=October 2020}}}}

===Non-shared family environment and environment outside the family===
Although parents treat their children differently, such differential treatment explains only a small amount of nonshared environmental influence. One suggestion is that children react differently to the same environment because of different genes. More likely influences may be the impact of peers and other experiences outside the family.{{sfn|Neisser et al.|1995}}<ref name="Plomin0103"/>

===Individual genes===
A very large proportion of the over 17,000 human genes are thought to have an effect on the development and functionality of the brain.<ref>{{cite journal |last1=Pietropaolo |first1=S. |last2=Crusio |first2=W. E. |author-link2=Wim Crusio |doi=10.1002/wcs.135 |pmid=26302082 |title=Genes and cognition |journal=[[Wiley Interdisciplinary Reviews: Cognitive Science]] |volume=2 |issue=3 |pages=345–352 |year=2010}}</ref> While a number of individual genes have been reported to be associated with IQ, none have a strong effect. Deary and colleagues (2009) reported that no finding of a strong single gene effect on IQ has been replicated.{{sfn|Deary|Johnson|Houlihan|2009}} Recent findings of gene associations with normally varying intellectual differences in adults and children continue to show weak effects for any one gene.<ref name="Davies2011">{{cite journal |vauthors=Davies G, Tenesa A, Payton A, Yang J, Harris SE, Liewald D, Ke X, Le Hellard S |year=2011 |title=Genome-wide association studies establish that human intelligence is highly heritable and polygenic |journal=Mol Psychiatry |volume=16 |issue=10 |pages=996–1005 |doi=10.1038/mp.2011.85 |pmid=21826061 |pmc=3182557 |display-authors=etal}}</ref><ref name="Benyamin2013">{{cite journal |display-authors=8 |vauthors= Benyamin B, Pourcain B, Davis OS, Davies G, Hansell NK, Brion MJ, Kirkpatrick RM, Cents RA, Franic S, Miller MB, Haworth CM, Meaburn E, Price TS, Evans DM, Timpson N, Kemp J, Ring S, McArdle W, Medland SE, Yang J, Harris SE, Liewald DC, Scheet P, Xiao X, Hudziak JJ, de Geus C, ((Wellcome Trust Case Control Consortium 2)), Jaddoe VW, Starr JM, Verhulst FC, Pennell C, Tiemeier H, Iacono WG, Palmer LJ, Montgomery GW, Martin NG, Boomsma DI, Posthuma D, McGue M, Wright MJ, Smith GD, Deary IJ, Plomin R, Visscher PM |year=2013 |title= Childhood intelligence is heritable, highly polygenic and associated with FNBP1L |journal=Mol Psychiatry |volume=19| issue=2| pages=253–258| doi=10.1038/mp.2012.184 |pmid=23358156 |pmc=3935975}}</ref>

A 2017 [[meta-analysis]] conducted on approximately 78,000 subjects identified 52 genes associated with intelligence.<ref>Sniekers S, Stringer S, Watanabe K, Jansen PR, Coleman JRI, Krapohl E, Taskesen E, Hammerschlag AR, Okbay A, Zabaneh D, Amin N, Breen G, Cesarini D, Chabris CF, Iacono WG, Ikram MA, Johannesson M, Koellinger P, Lee JJ, Magnusson PKE, McGue M, Miller MB, Ollier WER, Payton A, Pendleton N, Plomin R, Rietveld CA, Tiemeier H, van Duijn CM, Posthuma D. Genome-wide association meta-analysis of 78,308 individuals identifies new loci and genes influencing human intelligence. Nat Genet. 2017 Jul;49(7):1107-1112. doi: 10.1038/ng.3869. Epub 2017 May 22. Erratum in: Nat Genet. 2017 Sep 27;49(10 ):1558. PMID 28530673; PMCID: PMC5665562.</ref> [[FNBP1L]] is reported to be the single gene most associated with both adult and child intelligence.<ref>Benyamin B, Pourcain B, Davis OS, Davies G, Hansell NK, Brion MJ, Kirkpatrick RM, Cents RA, Franić S, Miller MB, Haworth CM, Meaburn E, Price TS, Evans DM, Timpson N, Kemp J, Ring S, McArdle W, Medland SE, Yang J, Harris SE, Liewald DC, Scheet P, Xiao X, Hudziak JJ, de Geus EJ; Wellcome Trust Case Control Consortium 2 (WTCCC2); Jaddoe VW, Starr JM, Verhulst FC, Pennell C, Tiemeier H, Iacono WG, Palmer LJ, Montgomery GW, Martin NG, Boomsma DI, Posthuma D, McGue M, Wright MJ, Davey Smith G, Deary IJ, Plomin R, Visscher PM. Childhood intelligence is heritable, highly polygenic and associated with FNBP1L. Mol Psychiatry. 2014 Feb;19(2):253-8. doi: 10.1038/mp.2012.184. Epub 2013 Jan 29. PMID 23358156; PMCID: PMC3935975.</ref>

===Gene-environment interaction===
[[David C. Rowe|David Rowe]] reported an interaction of genetic effects with [[socioeconomic status]], such that the heritability was high in high-SES families, but much lower in low-SES families.<ref name="Rowe">{{cite journal |last1=Rowe |first1=D. C. |last2=Jacobson |first2=K. C. |year=1999 |title=Genetic and environmental influences on vocabulary IQ: parental education level as moderator |journal=Child Development |volume=70 |issue=5 |pages=1151–62 |doi=10.1111/1467-8624.00084|pmid=10546338 |s2cid=10959764}}</ref> In the US, this has been replicated in infants,<ref name="Tucker-Drob2011">{{cite journal |last1=Tucker-Drob |first1=E. M. |last2=Rhemtulla |first2=M. |last3= Harden |first3=K. P. |last4=Turkheimer |first4=E. |last5=Fask |first5=D. |year=2011 |title=Emergence of a Gene x Socioeconomic Status Interaction on Infant Mental Ability Between 10 Months and 2 Years |journal=Psychological Science |volume=22 |issue=1| pages=125–33 |doi=10.1177/0956797610392926 |pmid=21169524 |pmc=3532898}}</ref> children,<ref>{{cite journal |last1=Turkheimer |first1=E. |last2=Haley |first2=A. |last3=Waldron |first3=M. |last4=D'Onofrio |first4=B. |last5=Gottesman |first5=I. I. |year=2003 |title=Socioeconomic status modifies heritability of IQ in young children |journal=Psychological Science |volume=14 |issue=6 |pages=623–628 |doi=10.1046/j.0956-7976.2003.psci_1475.x |pmid=14629696 |s2cid=11265284}}</ref> adolescents,<ref>{{cite journal |last1=Harden |first1=K. P. |last2=Turkheimer |first2=E. |last3=Loehlin |first3=J. C. |year=2005 |title=Genotype environment interaction in adolescents' cognitive ability |doi=10.1007/s10519-005-7287-9 |journal=Behavior Genetics |volume=35 |issue=6| page=804 |s2cid=189842802}}</ref> and adults.<ref>{{cite journal |last1=Bates |first1=Timothy C. |last2=Lewis |first2=Gary J. |last3=Weiss |first3=Alexander |date=3 September 2013 |title=Childhood Socioeconomic Status Amplifies Genetic Effects on Adult Intelligence |journal=Psychological Science |volume=24 |issue=10 |pages=2111–2116 |doi=10.1177/0956797613488394 |pmid=24002887 |s2cid=1873699 |url=https://www.pure.ed.ac.uk/ws/files/10602446/GxSES_Bates_Lewis_Weiss_2013_Psychological_Science.pdf|hdl=20.500.11820/52797d10-f0d4-49de-83e2-a9cc3493703d |hdl-access=free }}</ref> Outside the US, studies show no link between heritability and SES.<ref name=":0">{{cite journal |last1=Tucker-Drob |first1=Elliot M. |last2=Bates |first2=Timothy C. |title=Large Cross-National Differences in Gene × Socioeconomic Status Interaction on Intelligence |journal=Psychological Science |date=15 December 2015 |volume=27 |issue=2 |pages=138–149 |doi=10.1177/0956797615612727 |pmid=26671911 |pmc=4749462}}</ref> Some effects may even reverse sign outside the US.<ref name=":0" /><ref name="Hanscombe2012">{{cite journal |last1=Hanscombe |first1=K. B. |last2=Trzaskowski |first2=M. |last3=Haworth |first3=C. M. |last4=Davis |first4=O. S. |last5=Dale |first5=P. S. |last6=Plomin |first6=R. |year=2012 |title=Socioeconomic Status (SES) and Children's Intelligence (IQ): In a UK-Representative Sample SES Moderates the Environmental, Not Genetic, Effect on IQ. |journal=PLOS ONE |volume=7 |issue=2 |page=e30320 |doi=10.1371/journal.pone.0030320 |pmid=22312423 |pmc=3270016 |bibcode=2012PLoSO...730320H|doi-access=free }}</ref>

Dickens and Flynn (2001) have argued that genes for high IQ initiate an environment-shaping [[feedback|feedback cycle]], with genetic effects causing bright children to seek out more stimulating environments that then further increase their IQ. In Dickens' model, environment effects are modeled as decaying over time. In this model, the Flynn effect can be explained by an increase in environmental stimulation independent of it being sought out by individuals. The authors suggest that programs aiming to increase IQ would be most likely to produce long-term IQ gains if they enduringly raised children's drive to seek out cognitively demanding experiences.<ref name="DickensFlynn2001">{{cite journal |last1=Dickens |first1=William T. |last2=Flynn |first2=James R. |title=Heritability estimates versus large environmental effects: The IQ paradox resolved. |journal=Psychological Review |volume=108 |issue=2 |pages=346–69 |year=2001 |pmid=11381833 |doi=10.1037/0033-295X.108.2.346 |url=http://www.apa.org/journals/features/rev1082346.pdf |citeseerx=10.1.1.139.2436}}</ref><ref>{{cite journal|first1=William T. |last1=Dickens |first2=James R. |last2=Flynn |title=The IQ Paradox: Still Resolved |journal=Psychological Review |volume=109 |issue=4 |year=2002 |doi=10.1037/0033-295x.109.4.764 |pages=764–771 |url=http://www.brookings.edu/views/papers/dickens/20020205.pdf |url-status=dead |archive-url= https://web.archive.org/web/20070319031706/http://www.brookings.edu/views/papers/dickens/20020205.pdf |archive-date=19 March 2007}}</ref>