Editing Handedness (section)

=== Intelligence ===
{{Further|Handedness and mathematical ability|List of musicians who play left-handed}}
In his book ''Right-Hand, Left-Hand'', Chris McManus of [[University College London]] argues that the proportion of left-handers is increasing, and that an above-average quota of high achievers have been left-handed. He says that left-handers' brains are structured in a way that increases their range of abilities, and that the genes that determine left-handedness also govern development of the brain's language centers.<ref>{{cite web | url = http://www.righthandlefthand.com/ | first = Chris | last = McManus | name-list-style = vanc | title = Right-Hand, Left-Hand official website | archive-url = https://web.archive.org/web/20120504153055/http://www.righthandlefthand.com/ | archive-date=2012-05-04 | access-date = 1 June 2006 }}</ref>

Writing in ''[[Scientific American]]'', he states:
<blockquote>Studies in the U.K., U.S. and Australia have revealed that left-handed people differ from right-handers by only one IQ point, which is not noteworthy ... Left-handers' brains are structured differently from right-handers' in ways that can allow them to process language, spatial relations and emotions in more diverse and potentially creative ways. Also, a slightly larger number of left-handers than right-handers are especially gifted in music and math. A study of musicians in professional orchestras found a significantly greater proportion of talented left-handers, even among those who played instruments that seem designed for right-handers, such as violins. Similarly, studies of adolescents who took tests to assess mathematical giftedness found many more left-handers in the population.<ref>{{cite journal | first = Chris | last = McManus | name-list-style = vanc | date = 14 April 2012 | title = Is It True That Left-Handed People Are Smarter Than Right-Handed People? | journal = Scientific American Mind }}</ref></blockquote>

Left-handers are overrepresented among those with lower cognitive skills and mental impairments, with those with [[intellectual disability]] being roughly twice as likely to be left-handed, as well as generally lower cognitive and non-cognitive abilities amongst left-handed children.<ref name="Goodman 193–212">{{cite journal |last1=Goodman |first1=Joshua |title=The Wages of Sinistrality: Handedness, Brain Structure, and Human Capital Accumulation |journal=Journal of Economic Perspectives |date=1 November 2014 |volume=28 |issue=4 |pages=193–212 |doi=10.1257/jep.28.4.193 |doi-access=free }}</ref> Conversely, left-handers are also overrepresented in high IQ societies, such as [[Mensa International|Mensa]]. A 2005 study found that "approximately 20% of the members of Mensa are lefthanded, double the proportion in most general populations".<ref>{{cite journal |last1=Perelle |first1=Ira B. |last2=Ehrman |first2=Lee |title=On the Other Hand |journal=Behavior Genetics |date=May 2005 |volume=35 |issue=3 |pages=343–350 |doi=10.1007/s10519-005-3226-z |pmid=15864449 }}</ref>

Ghayas & Adil (2007) found that left-handers were significantly more likely to perform better on [[intelligence test]]s than right-handers and that right-handers also took more time to complete the tests.<ref>{{cite journal |last1=Ghayas |first1=Saba |first2=Adnan |last2=Adil |title=Effect of handedness on intelligence level of students |journal=Journal of the Indian Academy of Applied Psychology |volume=33 |issue=1 |date=2007 |pages=85–91 |url=https://www.researchgate.net/publication/233529472 }}</ref> In a systematic review and meta-analysis, Ntolka & Papadatou-Pastou (2018) found that right-handers had higher IQ scores, but that difference was negligible (about 1.5 points).<ref name="Ntolka & Papadatou-Pastou">{{cite journal | vauthors = Ntolka E, Papadatou-Pastou M | s2cid = 33792592 | title = Right-handers have negligibly higher IQ scores than left-handers: Systematic review and meta-analyses | journal = Neuroscience and Biobehavioral Reviews | volume = 84 | pages = 376–393 | date = January 2018 | pmid = 28826694 | doi = 10.1016/j.neubiorev.2017.08.007 }}</ref>

The prevalence of ''difficulties'' in left-right discrimination was investigated in a cohort of 2,720 adult members of [[Mensa International|Mensa]] and [[Intertel]] by Storfer.<ref name=":3">{{cite journal |last1=Storfer |first1=Miles D. |title=Problems in Left-Right Discrimination in a High-Iq Population |journal=Perceptual and Motor Skills |date=October 1995 |volume=81 |issue=2 |pages=491–497 |doi=10.1177/003151259508100226 |pmid=8570344 }}</ref> According to the study, 7.2% of the men and 18.8% of the women evaluated their left-right directional sense as poor or below average; moreover participants who were relatively ambidextrous experienced problems more frequently than did those who were more strongly left- or right-handed.<ref name=":3" /> The study also revealed an effect of age, with younger participants reporting more problems.<ref name=":3" />

==== Early childhood intelligence ====
Nelson, Campbell, and Michel studied infants and whether developing handedness during infancy correlated with language abilities in toddlers. In the article they assessed 38 infants and followed them through to 12 months and then again once they became toddlers from 18 to 24 months. They discovered that when a child developed a consistent use of their right or left hand during infancy (such as using the right hand to put the pacifier back in, or grasping random objects with the left hand), they were more likely to have superior language skills as a toddler. Children who became lateral later than infancy (i.e., when they were toddlers) showed normal development of language and had typical language scores. The researchers used [[Bayley scales of infant development|Bayley scales]] of infant and toddler development to assess the subjects.<ref name="Nelson_2014">{{cite journal | vauthors = Nelson EL, Campbell JM, Michel GF | title = Early handedness in infancy predicts language ability in toddlers | journal = Developmental Psychology | volume = 50 | issue = 3 | pages = 809–14 | date = March 2014 | pmid = 23855258 | pmc = 4059533 | doi = 10.1037/a0033803 }}</ref>