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{{Redirect2|Leftie|Rightie|the political orientations|Left-wing politics|and|Right-wing politics}}
[[File:SantaCruz-CuevaManos-P2210651b.jpg|thumb|right|Stenciled hands at the [[Cueva de las Manos]] in Argentina. Left hands make up over 90% of the artwork, demonstrating the prevalence of right-handedness.<ref>{{cite book|last1=Podestá|first1=María Mercedes|url=https://books.google.com/books?id=NuG-pvgnd6IC&dq=%22Cueva+de+las+Manos%22+left+hand&pg=PA11|title=El arte rupestre de Argentina indígena: Patagonia|last2=Raffino|first2=Rodolfo A.|last3=Paunero|first3=Rafael Sebastián|last4=Rolandi|first4=Diana S.|year=2005|publisher=Grupo Abierto Communicaciones|isbn=978-987-1121-16-8|language=es|access-date=2021-03-01|archive-date=2021-10-29|archive-url=https://web.archive.org/web/20211029010950/https://www.google.co.uk/gen_204?s=web&t=aft&atyp=csi&ei=10l7Ye-DE4K60PEP6uey8A8&rt=wsrt.491,aft.4960,prt.2585&imn=26&ima=10&imad=9&aftp=18869&bl=TGeo|url-status=live}}</ref>]]
[[File:تلميذة_تكتب_بيدها_اليسرى.jpg|thumb|right| A
In [[human biology]], '''handedness''' is an individual's preferential use of one [[hand]], known as the '''dominant hand''', due to it being stronger, faster or more [[Fine motor skill|dextrous]]. The other hand, comparatively often the weaker, less dextrous or simply less subjectively preferred, is called the '''non-dominant hand'''.<ref name= indiana>{{cite web | vauthors = Holder MK | url = http://www.indiana.edu/~primate/brain.html | title = What does Handedness have to do with Brain Lateralization (and who cares?) | archive-url = https://web.archive.org/web/20130326014257/http://www.indiana.edu/~primate/brain.html | archive-date=2013-03-26 | access-date = 11 August 2012 }}</ref><ref>{{cite web |title=dominant |url=https://www.merriam-webster.com/dictionary/dominant |website=Merriam-Webster Dictionary |publisher=Merriam-Webster |access-date=8 March 2017 |quote='''4''' : ''biology'' : being the one of a pair of bodily structures that is the more effective or predominant in action • ''dominant'' eye • used her ''dominant'' hand |archive-url=https://web.archive.org/web/20170308215527/https://www.merriam-webster.com/dictionary/dominant |archive-date=8 March 2017 |url-status=live }}</ref><ref>{{cite web |title=non- |url=https://www.merriam-webster.com/dictionary/non- |website=Merriam-Webster Dictionary |publisher=Merriam-Webster |access-date=8 March 2017 |quote=Definition of non- '''1''' : not : other than : reverse of : absence of • ''non''toxic • ''non''linear |archive-url=https://web.archive.org/web/20170308141644/https://www.merriam-webster.com/dictionary/non- |archive-date=8 March 2017 |url-status=live }}. ("Nondominant" is one of 945 words listed under "non-")</ref> In a study from 1975 on 7,688 children in US grades 1–6, left handers comprised 9.6% of the sample, with 10.5% of male children and 8.7% of female children being left-handed.<ref>{{Cite journal |last1=Hardyck |first1=C. |last2=Petrinovich |first2=L. F. |last3=Goldman |first3=R. D. |date=September 1976 |title=Left-handedness and cognitive deficit |journal=Cortex |volume=12 |issue=3 |pages=266–279 |doi=10.1016/s0010-9452(76)80008-1 |pmid=1000995 |s2cid=4477753 |doi-access=free | issn = 0010-9452}}</ref><ref name=":1">{{cite journal | vauthors = Scharoun SM, Bryden PJ | title = Hand preference, performance abilities, and hand selection in children | journal = Frontiers in Psychology | volume = 5 | issue = 82| pages = 82 | date = 2014 | pmid = 24600414 | pmc = 3927078 | doi = 10.3389/fpsyg.2014.00082 | doi-access = free }}</ref><ref name=bul0000229>{{cite journal |last1=Papadatou-Pastou |first1=Marietta |last2=Ntolka |first2=Eleni |last3=Schmitz |first3=Judith |last4=Martin |first4=Maryanne |last5=Munafò |first5=Marcus R. |last6=Ocklenburg |first6=Sebastian |last7=Paracchini |first7=Silvia |title=Human handedness: A meta-analysis. |journal=Psychological Bulletin |date=June 2020 |volume=146 |issue=6 |pages=481–524 |doi=10.1037/bul0000229 |pmid=32237881 |s2cid=214768754 |url=http://psyarxiv.com/5gjac/ |hdl=10023/19889 |hdl-access=free }}</ref> Overall, around 90% of people are right-handed.<ref>{{cite journal |last1=Pfeifer |first1=Lena Sophie |last2=Schmitz |first2=Judith |last3=Papadatou-Pastou |first3=Marietta |last4=Peterburs |first4=Jutta |last5=Paracchini |first5=Silvia |last6=Ocklenburg |first6=Sebastian |title=Handedness in twins: meta-analyses |journal=BMC Psychology |date=15 January 2022 |volume=10 |issue=1 |page=11 |doi=10.1186/s40359-021-00695-3 |pmc=8760823 |pmid=35033205 |doi-access=free }}</ref> Handedness is often defined by one's writing hand, as it is fairly common for people to prefer to do a particular task with a particular hand. There are people with true [[ambidexterity]] (equal preference of either hand), but it is rare—most people prefer using one hand for most purposes.
Most of the current research suggests that left-handedness has an [[epigenetic]] marker—a combination of genetics, biology and the environment.
Because the vast majority of the population is right-handed, many devices are designed for use by right-handed people, making their use by left-handed people more difficult.<ref name=":2" /> In many countries, left-handed people are or were required to write with their right hands. However, left-handed people have an advantage in [[sport]]s that
== Types ==
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Some non-human primates have a preferred hand for tasks, but they do not display a strong right-biased preference like modern humans, with individuals equally split between right-handed and left-handed preferences. When exactly a right handed preference developed in the human lineage is unknown, though it is known through various means that [[Neanderthal|Neanderthals]] had a right-handedness bias like modern humans. Attempts to determine handedness of early humans by analysing the morphology of lithic artefacts have been found to be unreliable.<ref>{{Cite journal |last1=Ruck |first1=Lana |last2=Broadfield |first2=Douglas C. |last3=Brown |first3=Clifford T. |date=2015-05-07 |title=Determining Hominid Handedness in Lithic Debitage: A Review of Current Methodologies |url=http://dx.doi.org/10.1179/2051618515y.0000000009 |journal=Lithic Technology |volume=40 |issue=3 |pages=171–188 |doi=10.1179/2051618515y.0000000009 |issn=0197-7261}}</ref>
== Causes ==
There are several theories of how handedness develops.
=== Genetic factors ===
Handedness displays a complex inheritance pattern. For example, if both parents of a child are left-handed, there is a 26% chance of that child being left-handed.<ref name="McManusChris">{{cite book | last = McManus | first = Chris | name-list-style = vanc | title=Right Hand, Left Hand | publisher=Phoenix Paperbacks | year=2003 | isbn=978-0753813553}}</ref> A large study of twins from 25,732 families by Medland et al. (2006) indicates that the [[heritability]] of handedness is roughly 24%.<ref>{{cite journal | vauthors = Medland SE, Duffy DL, Wright MJ, Geffen GM, Hay DA, Levy F, van-Beijsterveldt CE, Willemsen G, Townsend GC, White V, Hewitt AW, Mackey DA, Bailey JM, Slutske WS, Nyholt DR, Treloar SA, Martin NG, Boomsma DI | display-authors = 6 | title = Genetic influences on handedness: data from 25,732 Australian and Dutch twin families | journal = Neuropsychologia | volume = 47 | issue = 2 | pages = 330–7 | date = January 2009 | pmid = 18824185 | pmc = 2755095 | doi = 10.1016/j.neuropsychologia.2008.09.005 }}</ref>
Two theoretical single-gene models have been proposed to explain the patterns of inheritance of handedness, by Marian Annett<ref>{{Cite book |first=M. |last=Annett |s2cid=53411957 |title=Language lateralization and psychosis |chapter=The genetic basis of lateralization |year=2009 |pages=73–86 |doi=10.1017/CBO9780511576744.006 |editor1-last=Sommer |editor1-first=Iris E. C. |editor2-last=Kahn |editor2-first=René S. | name-list-style = vanc |isbn=9780511576744 |hdl=2381/4737 |url=https://figshare.com/articles/chapter/The_Genetic_Basis_of_Lateralization/10088477 }}</ref> of the [[University of Leicester]], and by Chris McManus<ref name="McManusChris" /> of [[University College London|UCL]].
However, growing evidence from [[genetic linkage|linkage]] and [[genome-wide association study|genome-wide association]] studies suggests that genetic variance in handedness cannot be explained by a single genetic [[Locus (genetics)|locus]].<ref>{{cite journal | vauthors = Francks C, DeLisi LE, Fisher SE, Laval SH, Rue JE, Stein JF, Monaco AP | title = Confirmatory evidence for linkage of relative hand skill to 2p12-q11 | journal = American Journal of Human Genetics | volume = 72 | issue = 2 | pages = 499–502 | date = February 2003 | pmid = 12596796 | pmc = 379245 | doi = 10.1086/367548 }}</ref><ref>{{cite journal | vauthors = Francks C, Maegawa S, Laurén J, Abrahams BS, Velayos-Baeza A, Medland SE, Colella S, Groszer M, McAuley EZ, Caffrey TM, Timmusk T, Pruunsild P, Koppel I, Lind PA, Matsumoto-Itaba N, Nicod J, Xiong L, Joober R, Enard W, Krinsky B, Nanba E, Richardson AJ, Riley BP, Martin NG, Strittmatter SM, Möller HJ, Rujescu D, St Clair D, Muglia P, Roos JL, Fisher SE, Wade-Martins R, Rouleau GA, Stein JF, Karayiorgou M, Geschwind DH, Ragoussis J, Kendler KS, Airaksinen MS, Oshimura M, DeLisi LE, Monaco AP | display-authors = 6 | title = LRRTM1 on chromosome 2p12 is a maternally suppressed gene that is associated paternally with handedness and schizophrenia | journal = Molecular Psychiatry | volume = 12 | issue = 12 | pages = 1129–39, 1057 | date = December 2007 | pmid = 17667961 | pmc = 2990633 | doi = 10.1038/sj.mp.4002053 }}</ref><ref>{{cite journal | vauthors = Van Agtmael T, Forrest SM, Williamson R | title = Parametric and non-parametric linkage analysis of several candidate regions for genes for human handedness | journal = European Journal of Human Genetics | volume = 10 | issue = 10 | pages = 623–30 | date = October 2002 | pmid = 12357333 | doi = 10.1038/sj.ejhg.5200851 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Warren DM, Stern M, Duggirala R, Dyer TD, Almasy L | s2cid = 11711104 | title = Heritability and linkage analysis of hand, foot, and eye preference in Mexican Americans | journal = Laterality | volume = 11 | issue = 6 | pages = 508–24 | date = November 2006 | pmid = 16966240 | doi = 10.1080/13576500600761056 }}</ref><ref>{{cite journal | vauthors = Laval SH, Dann JC, Butler RJ, Loftus J, Rue J, Leask SJ, Bass N, Comazzi M, Vita A, Nanko S, Shaw S, Peterson P, Shields G, Smith AB, Stewart J, DeLisi LE, Crow TJ | display-authors = 6 | title = Evidence for linkage to psychosis and cerebral asymmetry (relative hand skill) on the X chromosome | journal = American Journal of Medical Genetics | volume = 81 | issue = 5 | pages = 420–7 | date = September 1998 | pmid = 9754628 | doi = 10.1002/(SICI)1096-8628(19980907)81:5<420::AID-AJMG11>3.0.CO;2-E }}</ref><ref>{{cite journal | vauthors = Armour JA, Davison A, McManus IC | title = Genome-wide association study of handedness excludes simple genetic models | journal = Heredity | volume = 112 | issue = 3 | pages = 221–5 | date = March 2014 | pmid = 24065183 | pmc = 3931166 | doi = 10.1038/hdy.2013.93 }}</ref><ref>{{cite journal | vauthors = Eriksson N, Macpherson JM, Tung JY, Hon LS, Naughton B, Saxonov S, Avey L, Wojcicki A, Pe'er I, Mountain J | display-authors = 6 | title = Web-based, participant-driven studies yield novel genetic associations for common traits | journal = PLOS Genetics | volume = 6 | issue = 6 | pages = e1000993 | date = June 2010 | pmid = 20585627 | pmc = 2891811 | doi = 10.1371/journal.pgen.1000993 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Scerri TS, Brandler WM, Paracchini S, Morris AP, Ring SM, Richardson AJ, Talcott JB, Stein J, Monaco AP | display-authors = 6 | title = PCSK6 is associated with handedness in individuals with dyslexia | journal = Human Molecular Genetics | volume = 20 | issue = 3 | pages = 608–14 | date = February 2011 | pmid = 21051773 | pmc = 3016905 | doi = 10.1093/hmg/ddq475 | author-link3 = Silvia Paracchini }}</ref>{{excessive citations inline|date=March 2023}} From these studies, McManus et al. now conclude that handedness is [[polygenic]] and estimate that at least 40 [[Locus (genetics)|loci]] contribute to the trait.<ref>{{cite journal | vauthors = McManus IC, Davison A, Armour JA | title = Multilocus genetic models of handedness closely resemble single-locus models in explaining family data and are compatible with genome-wide association studies | journal = Annals of the New York Academy of Sciences | volume = 1288 | issue = 1 | pages = 48–58 | date = June 2013 | pmid = 23631511 | pmc = 4298034 | doi = 10.1111/nyas.12102 | bibcode = 2013NYASA1288...48M }}</ref>
Brandler et al. performed a [[genome-wide association study]] for a measure of relative hand skill and found that genes involved in the determination of [[left-right asymmetry]] in the body play a key role in handedness.<ref>{{cite journal | vauthors = Brandler WM, Morris AP, Evans DM, Scerri TS, Kemp JP, Timpson NJ, St Pourcain B, Smith GD, Ring SM, Stein J, Monaco AP, Talcott JB, Fisher SE, Webber C, Paracchini S | display-authors = 6 | title = Common variants in left/right asymmetry genes and pathways are associated with relative hand skill | journal = PLOS Genetics | volume = 9 | issue = 9 | pages = e1003751 | date = September 2013 | pmid = 24068947 | pmc = 3772043 | doi = 10.1371/journal.pgen.1003751 | doi-access = free }}</ref> Brandler and [[Silvia Paracchini|Paracchini]] suggest the same mechanisms that determine left-right asymmetry in the body (e.g. [[nodal signaling]] and [[ciliogenesis]]) also play a role in the development of [[brain asymmetry]]
(handedness being a reflection of brain asymmetry for motor function).<ref>{{cite journal | vauthors = Brandler WM, Paracchini S | title = The genetic relationship between handedness and neurodevelopmental disorders | journal = Trends in Molecular Medicine | volume = 20 | issue = 2 | pages = 83–90 | date = February 2014 | pmid = 24275328 | pmc = 3969300 | doi = 10.1016/j.molmed.2013.10.008 }}</ref>
In 2019, Wiberg et al. performed a genome-wide association study and found that handedness was significantly associated with four loci, three of them in genes encoding proteins involved in brain development.<ref>{{cite journal | vauthors = Wiberg A, Ng M, Al Omran Y, Alfaro-Almagro F, McCarthy P, Marchini J, Bennett DL, Smith S, Douaud G, Furniss D | display-authors = 6 | title = Handedness, language areas and neuropsychiatric diseases: insights from brain imaging and genetics | journal = Brain | volume = 142 | issue = 10 | pages = 2938–2947 | date = October 2019 | pmid = 31504236 | pmc = 6763735 | doi = 10.1093/brain/awz257 }}</ref>
=== Prenatal hormone exposure ===
Four studies have indicated that individuals who have had in-utero exposure to [[diethylstilbestrol]] (a synthetic [[estrogen]] based medication used between 1940 and 1971) were more likely to be left-handed over the clinical control group. Diethylstilbestrol animal studies "suggest that estrogen affects the developing brain, including the part that governs sexual behavior and right and left dominance".<ref>{{cite journal |last1=Titus-Ernstoff |first1=Linda |last2=Perez |first2=Kimberly |last3=Hatch |first3=Elizabeth E. |last4=Troisi |first4=Rebecca |last5=Palmer |first5=Julie R. |last6=Hartge |first6=Patricia |last7=Hyer |first7=Marianne |last8=Kaufman |first8=Raymond |last9=Adam |first9=Ervin |last10=Strohsnitter |first10=William |last11=Noller |first11=Kenneth |last12=Pickett |first12=Kate E. |last13=Hoover |first13=Robert |title=Psychosexual Characteristics of Men and Women Exposed Prenatally to Diethylstilbestrol |journal=Epidemiology |date=March 2003 |volume=14 |issue=2 |pages=155–160 |doi=10.1097/01.EDE.0000039059.38824.B2 |pmid=12606880 |s2cid=31181675 |doi-access=free }}</ref><ref>{{cite journal | vauthors = Scheirs JG, Vingerhoets AJ | title = Handedness and other laterality indices in women prenatally exposed to DES | journal = Journal of Clinical and Experimental Neuropsychology | volume = 17 | issue = 5 | pages = 725–30 | date = October 1995 | pmid = 8557813 | doi = 10.1080/01688639508405162 }}</ref><ref>{{cite journal | vauthors = Schachter SC | title = Handedness in women with intrauterine exposure to diethylstilbestrol | journal = Neuropsychologia | volume = 32 | issue = 5 | pages = 619–23 | date = May 1994 | pmid = 8084419 | doi = 10.1016/0028-3932(94)90149-x | s2cid = 44387790 }}</ref><ref>{{cite journal | vauthors = Smith LL, Hines M | title = Language lateralization and handedness in women prenatally exposed to diethylstilbestrol (DES) | journal = Psychoneuroendocrinology | volume = 25 | issue = 5 | pages = 497–512 | date = July 2000 | pmid = 10818283 | doi = 10.1016/s0306-4530(00)00005-6 | s2cid = 44323126 }}</ref>
=== Ultrasound ===
Another theory is that [[Medical ultrasonography|ultrasound]] may sometimes affect the brains of unborn children, causing higher rates of left-handedness in children whose mothers receive ultrasound during pregnancy. Research suggests there may be a weak association between [[Obstetrical ultrasonography|ultrasound screening]] (sonography used to check the healthy development of the fetus and mother) and left-handedness.<ref name="Salvesen 2011">{{cite journal | vauthors = Salvesen KÅ | s2cid = 5135695 | title = Ultrasound in pregnancy and non-right handedness: meta-analysis of randomized trials | journal = Ultrasound in Obstetrics & Gynecology | volume = 38 | issue = 3 | pages = 267–71 | date = September 2011 | pmid = 21584892 | doi = 10.1002/uog.9055 | doi-access = free }}</ref>
=== Epigenetic markers ===
[[Twin study|Twin studies]] indicate that genetic factors explain 25% of the variance in handedness, and environmental factors the remaining 75%.<ref name="Medland">{{cite journal |last1=Medland |first1=Sarah E. |last2=Duffy |first2=David L. |last3=Wright |first3=Margaret J. |last4=Geffen |first4=Gina M. |last5=Martin |first5=Nicholas G. |date=1 February 2006 |title=Handedness in Twins: Joint Analysis of Data From 35 Samples |journal=Twin Research and Human Genetics |volume=9 |issue=1 |pages=46–53 |doi=10.1375/183242706776402885 |pmid=16611467 |s2cid=38843437 |doi-access=free}}</ref> While the molecular basis of handedness [[epigenetics]] is largely unclear, Ocklenburg et al. (2017) found that asymmetric [[DNA methylation|methylation]] of [[CpG site]]s plays a key role for [[gene expression]] asymmetries related to handedness.<ref name="Sun">{{cite journal |vauthors=Sun T, Collura RV, Ruvolo M, Walsh CA |date=July 2006 |title=Genomic and evolutionary analyses of asymmetrically expressed genes in human fetal left and right cerebral cortex |journal=Cerebral Cortex |volume=16 |issue=Suppl 1 |pages=i18-25 |doi=10.1093/cercor/bhk026 |pmid=16766703 |doi-access=free}}</ref><ref name="Ocklenburg">{{cite journal |display-authors=6 |vauthors=Ocklenburg S, Schmitz J, Moinfar Z, Moser D, Klose R, Lor S, Kunz G, Tegenthoff M, Faustmann P, Francks C, Epplen JT, Kumsta R, Güntürkün O |date=February 2017 |title=Epigenetic regulation of lateralized fetal spinal gene expression underlies hemispheric asymmetries |journal=eLife |volume=6 |doi=10.7554/eLife.22784 |pmc=5295814 |pmid=28145864 |doi-access=free}}</ref>
=== Language dominance ===
One common handedness theory is the brain hemisphere division of labor. In most people, the left side of the brain controls speaking. The theory suggests it is more efficient for the brain to divide major tasks between the hemispheres—thus most people may use the non-speaking (right) hemisphere for perception and gross motor skills. As speech is a very complex motor control task, the specialised fine motor areas controlling speech are most efficiently used to also control fine motor movement in the dominant hand. As the right hand is controlled by the left hemisphere (and the left hand is controlled by the right hemisphere) most people are, therefore right-handed. The theory depends on left-handed people having a reversed organisation.<ref name="book">{{cite book |last=Banich |first=Marie |url=https://archive.org/details/neuropsychologyn00bani |title=Neuropsychology: The Neural Bases of Mental Function |publisher=Houghton Mifflin |year=1997 |isbn=9780395666999 |author-link= |url-access=registration |name-list-style=vanc}}</ref> However, the majority of left-handers have been found to have left-hemisphere language dominance—just like right-handers.<ref>{{cite journal |last1=Rasmussen |first1=T |last2=Milner |first2=B |date=1977 |title=The role of early left-brain injury in determining lateralization of cerebral speech functions |url=https://pubmed.ncbi.nlm.nih.gov/101116/ |journal=Annals of the New York Academy of Sciences |volume=30 |issue=299 |pages=355–369 |bibcode=1977NYASA.299..355R |doi=10.1111/j.1749-6632.1977.tb41921.x |pmid=101116 |s2cid=10981238}}</ref><ref>{{cite journal |last1=Carey |first1=David |last2=Johnstone |first2=Leah |date=2014 |title=Quantifying cerebral asymmetries for language in dextrals and adextrals with random-effects meta analysis |journal=Frontiers in Psychology |volume=5 |page=1128 |doi=10.3389/fpsyg.2014.01128 |pmc=4219560 |pmid=25408673 |doi-access=free}}</ref> Only around 30% of left-handers are not left-hemisphere dominant for language. Some of those have reversed brain organisation, where the verbal processing takes place in the right-hemisphere and visuospatial processing is dominant to the left hemisphere.<ref>{{cite journal |last1=Cai |first1=Q |last2=Van Der Haegen |first2=L |last3=Brysbaert |first3=M |date=2013 |title=Complementary hemispheric specialization for language production and visuospatial attention |journal=PNAS |volume=110 |issue=4 |pages=322–330 |doi=10.1073/pnas.1212956110 |pmc=3557046 |pmid=23297206 |doi-access=free}}</ref> Others have more ambiguous bilateral organisation, where both hemispheres do parts of typically lateralised functions. When tasks designed to investigate lateralisation (preference for handedness) are averaged across a group of left-handers, the overall effect is that left-handers show the same pattern of data as right-handers, but with a reduced asymmetry.<ref>{{cite journal |last1=Karlsson |first1=Emma M. |last2=Johnstone |first2=Leah T. |last3=Carey |first3=David P. |title=The depth and breadth of multiple perceptual asymmetries in right handers and non-right handers |journal=Laterality |date=2 November 2019 |volume=24 |issue=6 |pages=707–739 |doi=10.1080/1357650X.2019.1652308 |pmid=31399020 |s2cid=199519317 |url=https://research.bangor.ac.uk/portal/en/researchoutputs/the-depth-and-breadth-of-multiple-perceptual-asymmetries-in-right-handers-and-nonright-handers(15fe822a-a733-41f7-b817-70760ca7001d).html }}</ref> This finding is likely due to the small proportion of left-handers who have atypical brain organisation.{{cn|date=May 2024}} The majority of the evidence comes from literature assessing oral language production and comprehension. When it comes to writing, findings from recent studies were inconclusive for a difference in lateralization for writing between left-handers and right-handers. <ref>{{cite journal | vauthors = Papadopoulou AK, Samsouris C, Vlachos F, Badcock N, Phylactou P, Papadatou-Pastou | title = Exploring cerebral laterality of writing and the relationship to handedness: a functional transcranial Doppler ultrasound investigation | journal = Laterality | volume = 29 | issue = 1 | pages = 117–150 | date = November 2023 | doi = 10.1080/1357650X.2023.2284407| pmid = 38112692 }}</ref>
== Developmental timeline ==
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==== 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>
===Music===
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=== Income ===
In a 2006 better correlate with the lateralization for writing compared to the other
In a 2014 study published by the [[National Bureau of Economic Research]], [[Harvard University|Harvard]] economist Joshua Goodman finds that left-handed people earn 10 to 12 percent less over the course of their lives than right-handed people. Goodman attributes this disparity to higher rates of emotional and behavioral problems in left-handed people.<ref name="Goodman 193–212"/>
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