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'{{short description|Better performance or individual preference for use of a hand}} {{About|left- and right-handedness in humans|other uses|Handedness (disambiguation)}} {{redirect|Left-hander|other uses|Left-Hander (disambiguation)}} {{redirect|Leftie|the political orientation|Left-wing politics}} In [[human biology]], '''handedness''' is the better, faster, or more precise performance or individual preference for use of a hand, known as the '''dominant hand'''. The incapable, less capable or less preferred hand 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> Right-handedness is most common; about 90% of people are right-handed.<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 }}</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 |url=http://psyarxiv.com/5gjac/ }}</ref> Handedness is often defined by one's writing hand, as it is fairly common for people to prefer to do some tasks with each hand. There are examples of true [[ambidexterity]] (equal use of either hand), but it is rare—most people prefer 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. Left-handed people are also more prone to certain health problems. However, left-handed people have an advantage in [[sport]]s that involve aiming at a target, as their opponents are more accustomed to the right-handed majority. As a result, they are over-represented in [[baseball]], [[tennis]], [[fencing]], [[cricket]] and [[boxing]].<ref>{{Cite web |url=https://curiosity.com/topics/heres-why-left-handed-athletes-dominate-one-on-one-sports-curiosity/ |title=Here's Why Left-Handed Athletes Dominate One-on-One Sports |website=Curiosity.com |archive-url=https://web.archive.org/web/20191114194413/https://curiosity.com/topics/heres-why-left-handed-athletes-dominate-one-on-one-sports-curiosity/ |archive-date=14 November 2019 }}{{unreliable source?|date=November 2020}}</ref> == Types == * ''Right-handedness'' is by far the most common type. Right-handed people are more skillful with their right hands. Studies suggest that approximately 90% of people are right-handed.<ref name=bul0000229/><ref name="sciamerican">{{cite web|url=http://www.scientificamerican.com/article.cfm?id=why-are-more-people-right|title=Why are more people right-handed?|access-date=2008-04-14|work=Scientific American|year=1997| vauthors = Holder MK |archive-url=https://www.webcitation.org/6HxBj02LL?url=http://www.scientificamerican.com/article.cfm?id=why-are-more-people-right|archive-date=2013-07-08|url-status=live}}</ref> * ''Left-handedness'' is far less common than right-handedness. Studies suggest that approximately 10% of people are left-handed.<ref name=bul0000229/><ref>{{cite journal | vauthors = Hardyck C, Petrinovich LF | title = Left-handedness | journal = Psychological Bulletin | volume = 84 | issue = 3 | pages = 385–404 | date = May 1977 | pmid = 859955 | doi = 10.1037/0033-2909.84.3.385 }}</ref> * ''[[Cross-dominance]] or mixed-handedness'' is the change of hand preference between tasks. This is very uncommon, with about a 1% prevalence.<ref name= annett>{{cite book |last=Annett |first=Marian | name-list-style = vanc |year=2002 |title=Handedness and Brain Asymmetry | publisher = Psychology Press}}</ref> * ''[[Ambidexterity]]'', equal ability in both hands, is rare. Those who learn it still tend to favor their originally dominant hand. This is very uncommon, with about a 1% prevalence.{{citation needed|date=April 2020}} == Measurement == Handedness may be measured behaviourally (performance measures) or through questionnaires (preference measures). The [[Edinburgh Handedness Inventory]] has been used since 1971 but contains many dated questions and is hard to score. The longer Waterloo Handedness Questionnaire is not widely accessible. More recently, the Flinders Handedness Survey (FLANDERS) has been developed.<ref>{{cite journal |last1=Nicholls |first1=Michael E.R. |last2=Thomas |first2=Nicole A. |last3=Loetscher |first3=Tobias |last4=Grimshaw |first4=Gina M. |title=The Flinders Handedness survey (FLANDERS): A brief measure of skilled hand preference |journal=Cortex |date=November 2013 |volume=49 |issue=10 |pages=2914–2926 |doi=10.1016/j.cortex.2013.02.002 |pmid=23498655 |s2cid=4986724 }}</ref> == Causes == There are several theories of how handedness develops. Occurrences during [[prenatal development]] may be important; researchers studied fetuses in utero and determined that handedness in the womb was a very accurate predictor of handedness after birth.<ref>{{cite journal | vauthors = Hepper PG, Wells DL, Lynch C | s2cid = 805957 | title = Prenatal thumb sucking is related to postnatal handedness | journal = Neuropsychologia | volume = 43 | issue = 3 | pages = 313–5 | year = 2005 | pmid = 15707608 | doi = 10.1016/j.neuropsychologia.2004.08.009 }}</ref> In a 2013 study, 39% of infants (6 to 14 months) and 97% of toddlers (18 to 24 months) demonstrated a hand preference.<ref>{{cite journal | vauthors = Nelson EL, Campbell JM, Michel GF | title = Unimanual to bimanual: tracking the development of handedness from 6 to 24 months | journal = Infant Behavior & Development | volume = 36 | issue = 2 | pages = 181–8 | date = April 2013 | pmid = 23454419 | pmc = 3615031 | doi = 10.1016/j.infbeh.2013.01.009 }}</ref> === Division of labor === 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 work requiring fine motor skills, facilitating the use of speech while working, and resulting in right-handedness. The theory implies that left-handed people have a reversed brain division of labor.<ref name="book">{{cite book |last=Banich |first=Marie | name-list-style = vanc |author-link=Marie Banich |year=1997 |title=Neuropsychology: The Neural Bases of Mental Function|url=https://archive.org/details/neuropsychologyn00bani |url-access=registration }}</ref> Verbal processing in right-handed people occurs mostly in the left hemisphere, whereas visuospatial processing is done mostly in the right. Left-handed people have a heterogeneous brain organization where the hemispheres are either organized as in right-handers, but with hemispheres reversed; or such that both hemispheres are used for verbal processing. An average taken across all types of left-handedness shows that left-handers are less [[Lateralization of brain function|lateralized]].<ref name=book/> === 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 }}</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 }}</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> 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 }}</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> === Epigenetic factors === [[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. |title=Handedness in Twins: Joint Analysis of Data From 35 Samples |journal=Twin Research and Human Genetics |date=1 February 2006 |volume=9 |issue=1 |pages=46–53 |doi=10.1375/183242706776402885 |pmid=16611467 |s2cid=38843437 }}</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 | title = Genomic and evolutionary analyses of asymmetrically expressed genes in human fetal left and right cerebral cortex | journal = Cerebral Cortex | volume = 16 Suppl 1 | issue = Suppl 1 | pages = i18-25 | date = July 2006 | pmid = 16766703 | doi = 10.1093/cercor/bhk026 | doi-access = free }}</ref><ref name="Ocklenburg">{{cite journal | 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 | display-authors = 6 | title = Epigenetic regulation of lateralized fetal spinal gene expression underlies hemispheric asymmetries | journal = eLife | volume = 6 | date = February 2017 | pmid = 28145864 | pmc = 5295814 | doi = 10.7554/eLife.22784 }}</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 }}</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> === Prenatal vestibular asymmetry === Previc, after reviewing a large number of studies, found evidence that the position of the fetus in the final trimester and a baby's subsequent birth position can affect handedness. About two-thirds of fetuses present with their left [[occiput]] (back of the head) at birth. This partly explains why prematurity results in a decrease in right-handedness. Previc argues that asymmetric prenatal positioning creates asymmetric stimulation of the vestibular system, which is involved in the development of handedness. In fact, every major disorder in which patients show reduced right-handedness is associated with either [[vestibular system|vestibular]] abnormalities or delay,<ref>{{cite journal | vauthors = Previc FH | title = Nonright‐handedness, central nervous system and related pathology, and its lateralization: A reformulation and synthesis. | journal = Developmental Neuropsychology | date = January 1996 | volume = 12 | issue = 4 | pages = 443–515 | doi = 10.1080/87565649609540663 }}</ref> and asymmetry of the [[vestibular cortex]] is strongly correlated with the direction of handedness.<ref>{{cite journal | vauthors = Dieterich M, Bense S, Lutz S, Drzezga A, Stephan T, Bartenstein P, Brandt T | title = Dominance for vestibular cortical function in the non-dominant hemisphere | journal = Cerebral Cortex | volume = 13 | issue = 9 | pages = 994–1007 | date = September 2003 | pmid = 12902399 | doi = 10.1093/cercor/13.9.994 | doi-access = free }}</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> == Developmental timeline {{Anchor|Handedness developmental timeline}} == Infants have been observed to fluctuate heavily when choosing a hand to lead in grasping and object manipulation tasks, especially in one- versus two-handed grasping. Between 36 and 48 months, there is a significant decline in variability between handedness in one-handed grasping; it can be seen earlier in two-handed manipulation. Children of 18–36 months showed more hand preference when performing bi-manipulation tasks than with simple grasping.<ref name=":0">{{Cite journal|last1=Fagard|first1=Jacqueline|last2=Lockman|first2=Jeffrey J. | name-list-style = vanc |title=The effect of task constraints on infants' (bi)manual strategy for grasping and exploring objects|journal=Infant Behavior and Development |volume=28|issue=3|pages=305–315 |doi=10.1016/j.infbeh.2005.05.005|year=2005}}</ref> The decrease in handedness variability in children of 36–48 months may be attributable to preschool or kindergarten attendance, due to increased single-hand activities such as writing and coloring.<ref name=":0" /> Scharoun and Bryden noted that right-handed preference increases with age up to the teenage years.<ref name=":1" /> == Correlation with other factors == === 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> Conversely, Joshua Goodman found that evidence for left-handers was overrepresented amongst those with higher cognitive skills, such as Mensa members and higher-performing takers of SAT and MCAT tests, due to methodological and sampling issues in studies. He also found that left-handers were overrepresented among those with lower cognitive skills and mental impairments, with those with [[Intellectual disability]] (ID) 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 |url=http://nrs.harvard.edu/urn-3:HUL.InstRepos:7779971 }}</ref> In a systematic review and meta-analysis, Ntolka and Papadatou-Pastou 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> ==== 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. What they discovered was 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.<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> The researchers used [[Bayley scales of infant development|Bayley scales]] of infant and toddler development to assess all the subjects. ===Music=== In two studies, [[Diana Deutsch]] found that left-handers, particularly those with mixed hand preference, performed significantly better than right-handers in musical memory tasks.<ref name="Deutsch1978">{{cite journal |last1=Deutsch |first1=D |title=Pitch memory: an advantage for the left-handed |journal=Science |date=3 February 1978 |volume=199 |issue=4328 |pages=559–560 |doi=10.1126/science.622558 |pmid=622558 |bibcode=1978Sci...199..559D |s2cid=2274951 }}</ref><ref name="Deutsch1980">{{cite book |doi=10.1016/B978-0-12-343150-9.50016-0 |chapter=Handedness and Memory for Tonal Pitch |title=Neuropsychology of Left-Handedness |year=1980 |last1=Deutsch |first1=Diana |pages=263–271 |isbn=978-0-12-343150-9 }}</ref> There are also handedness differences in perception of musical patterns. Left-handers as a group differ from right-handers, and are more heterogeneous than right-handers, in perception of certain stereo illusions, such as the [[octave illusion]], the [[scale illusion]], and the [[glissando illusion]]. <ref name="Deutsch2019"> {{cite book | vauthors = Deutsch D | title = Musical Illusions and Phantom Words: How Music and Speech Unlock Mysteries of the Brain | year = 2019 | url = https://global.oup.com/academic/product/musical-illusions-and-phantom-words-9780190206833 | publisher = Oxford University Press | lccn = 2018051786 | author-link = Diana Deutsch | isbn = 9780190206833 }}{{page needed|date=November 2020}} </ref> ===Health=== Left-handed people are much more likely to have several specific physical and mental disorders and health problems. For example: Lower-birth-weight and complications at birth are positively correlated with left-handedness.<ref name="news.harvard.edu">{{cite web | first = Alvin | last = Powell | name-list-style = vanc |url=http://news.harvard.edu/gazette/story/2015/01/a-leftys-lament/|title=A lefty's lament|work=Harvard Gazette|date=2015-01-30|access-date=2015-12-29|archive-url=https://web.archive.org/web/20151223014439/http://news.harvard.edu/gazette/story/2015/01/a-leftys-lament/|archive-date=2015-12-23|url-status=live}}</ref> A variety of neuropsychiatric and developmental disorders like [[autism spectrum]] disorders, [[Major depressive disorder|depression]], [[bipolar disorder]], [[anxiety disorders]], [[schizophrenia]], and [[alcoholism]] has been associated with left- and mixed-handedness.<ref name="Ocklenburg"/><ref>{{cite journal | vauthors = Hirnstein M, Hugdahl K | title = Excess of non-right-handedness in schizophrenia: meta-analysis of gender effects and potential biases in handedness assessment | journal = The British Journal of Psychiatry | volume = 205 | issue = 4 | pages = 260–7 | date = October 2014 | pmid = 25274314 | doi = 10.1192/bjp.bp.113.137349 | doi-access = free | author-link2 = Kenneth Hugdahl }}</ref> A 2012 study showed that nearly 40% of children with [[cerebral palsy]] were left-handed,<ref>{{cite journal | vauthors = Lin KR, Prabhu V, Shah H, Kamath A, Joseph B | s2cid = 6972136 | title = Handedness in diplegic cerebral palsy | journal = Developmental Neurorehabilitation | volume = 15 | issue = 5 | pages = 386–9 | date = 2015 | pmid = 22758776 | doi = 10.3109/17518423.2012.696736 }}</ref> while another study demonstrated that left-handedness was associated with a 62 percent increased risk of [[Parkinson's disease]] in women, but not in men.<ref>{{cite journal | vauthors = Gardener H, Gao X, Chen H, Schwarzschild MA, Spiegelman D, Ascherio A | title = Prenatal and early life factors and risk of Parkinson's disease | journal = Movement Disorders | volume = 25 | issue = 11 | pages = 1560–7 | date = August 2010 | pmid = 20740569 | pmc = 3132935 | doi = 10.1002/mds.23339 }}</ref> Another study suggests that the risk of developing [[multiple sclerosis]] increases for left-handed women, but the effect is unknown for men at this point.<ref>{{cite journal | vauthors = Gardener H, Munger K, Chitnis T, Spiegelman D, Ascherio A | title = The relationship between handedness and risk of multiple sclerosis | journal = Multiple Sclerosis | volume = 15 | issue = 5 | pages = 587–92 | date = May 2009 | pmid = 19389750 | pmc = 2771381 | doi = 10.1177/1352458509102622 }}</ref> Left-handed women have a higher risk of [[breast cancer]] than right-handed women and the effect is greater in post-menopausal women.<ref>{{cite journal | vauthors = Fritschi L, Divitini M, Talbot-Smith A, Knuiman M | title = Left-handedness and risk of breast cancer | journal = British Journal of Cancer | volume = 97 | issue = 5 | pages = 686–7 | date = September 2007 | pmid = 17687338 | pmc = 2360366 | doi = 10.1038/sj.bjc.6603920 }}</ref> At least one study maintains that left-handers are more likely to suffer from [[heart disease]], and are more likely to have reduced longevity from [[cardiovascular]] causes.<ref>{{cite journal | vauthors = Hughes JR, Dorner E, Wind M | s2cid = 21369165 | title = Is the decreased longevity among left-handers related to an increase in heart disease? | journal = Clinical EEG and Neuroscience | volume = 39 | issue = 4 | pages = 182–4 | date = October 2008 | pmid = 19044215 | doi = 10.1177/155005940803900406 }}</ref> Left-handers are more likely to suffer bone fractures.<ref>{{cite journal | vauthors = Luetters CM, Kelsey JL, Keegan TH, Quesenberry CP, Sidney S | s2cid = 32654176 | title = Left-handedness as a risk factor for fractures | journal = Osteoporosis International | volume = 14 | issue = 11 | pages = 918–22 | date = November 2003 | pmid = 14530828 | doi = 10.1007/s00198-003-1450-z }}</ref> One [[systematic review]] concluded: "Left-handers showed no systematic tendency to suffer from disorders of the immune system".<ref>{{cite web|url=https://www.psychologytoday.com/blog/brain-myths/201303/three-myths-and-three-facts-about-left-handers|title=Three Myths and Three Facts About Left-Handers|work=Psychology Today}}</ref> As handedness is a highly heritable trait associated with various medical conditions, and because many of these conditions could have presented a Darwinian fitness challenge in ancestral populations, this indicates left-handedness may have previously been rarer than it currently is, due to natural selection. However, on average, left-handers have been found to have an advantage in fighting and competitive, interactive sports, which could have increased their reproductive success in ancestral populations.<ref>{{cite news|last1=Knight|first1=Will | name-list-style = vanc |title=Left-handers win in hand-to-hand combat|url=https://www.newscientist.com/article/dn6773-left-handers-win-in-hand-to-hand-combat/|access-date=27 October 2016|work=[[New Scientist]]|date=8 December 2004|archive-url=https://web.archive.org/web/20161027125658/https://www.newscientist.com/article/dn6773-left-handers-win-in-hand-to-hand-combat/|archive-date=27 October 2016|url-status=live}}</ref> === Income === In a 2006 U.S. study, researchers from [[Lafayette College]] and [[Johns Hopkins University]] concluded that there was no statistically significant correlation between handedness and earnings for the general population, but among college-educated people, left-handers earned 10 to 15% more than their right-handed counterparts.<ref>{{cite web | last = Waldfogel | first = Joel | name-list-style = vanc | date = 15 August 2006 | url = http://www.slate.com/id/2147842 | title = Sinister and Rich: The evidence that lefties earn more | archive-url = https://web.archive.org/web/20100112084036/http://www.slate.com/id/2147842 | archive-date=2010-01-12 | work = [[Slate (magazine)|Slate]] }}</ref> However, more recently, 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"/> === Left-handedness and sports === {{more citations needed section|date=January 2013}} {{See also|Southpaw stance}} Interactive sports such as table tennis, badminton and cricket have an overrepresentation of left-handedness, while non-interactive sports such as swimming show no overrepresentation. Smaller physical distance between participants increases the overrepresentation. In [[fencing]], about half the participants are left-handed.<ref name=AEP>{{cite book | vauthors = Widermann D, Barton RA, Hill RA | chapter = Evolutionary perspectives on sport and competition | chapter-url = https://books.google.com/books?id=I20uPfEjsNQC&pg=PA290 | veditors = Roberts SC | doi = 10.1093/acprof:oso/9780199586073.001.0001 | title = Applied Evolutionary Psychology | year = 2011 | publisher = Oxford University Press| isbn = 9780199586073 }}</ref> The term ''southpaw'' is sometimes used to refer to a left-handed individual, especially in [[baseball]] and [[boxing]].<ref>{{cite dictionary |date=June 2011 |title=southpaw, n. and adj. |dictionary=Oxford English Dictionary |publisher=Oxford University Press |url=https://www.oed.com/view/Entry/185300 |url-access=subscription |access-date=5 July 2020 |edition=3rd}}</ref> Other, sports-specific factors may [[Confounding|increase or decrease]] the advantage left-handers usually hold in one-on-one situations: * In [[cricket]], the overall advantage of a bowler's left-handedness exceeds that resulting from experience alone: even disregarding the experience factor (''i.e.'', even for a batsman whose experience against left-handed bowlers equals his experience against right-handed bowlers), a left-handed bowler challenges the [[Mode (statistics)|average]] (''i.e.'', right-handed) batsman more than a right-handed bowler does, because the angle of a bowler's delivery to an opposite-handed batsman is much more penetrating than that of a bowler to a same-handed batsman (see [[Wasim Akram]]).{{citation needed|date=January 2013}} * In [[baseball]], a right-handed pitcher's [[curve ball]] will break away from a right-handed batter and towards a left-handed batter. While studies of handedness show that only 10% of the general population is left-handed, the proportion of left-handed [[MLB]] players is closer to 39% of hitters and 28% of pitchers, according to 2012 data.<ref>{{cite web |last1=Peterson |first1=Dan | name-list-style = vanc |title=Righties vs Lefties - The Importance Of Handedness Training In Hitting |url=https://www.gamesensesports.com/knowledge/2017/3/17/righties-vs-lefties-the-importance-of-handedness-training-in-baseball-hitting |website=Game Sense Sports |publisher=Game Sense Sports |access-date=3 April 2019 |archive-url=https://web.archive.org/web/20190403165517/https://www.gamesensesports.com/knowledge/2017/3/17/righties-vs-lefties-the-importance-of-handedness-training-in-baseball-hitting |archive-date=3 April 2019 |url-status=live }}</ref> Historical [[batting average (baseball)|batting averages]] show that left-handed batters have a slight advantage over right-handed batters when facing right-handed pitchers.<ref>{{cite web |url=https://www.baseball-reference.com/leagues/split.cgi?t=b&lg=MLB&year=2012#plato |title=2012 Major League Baseball Batting Splits |website=Baseball Reference |access-date=6 March 2013 |archive-url=https://web.archive.org/web/20150909022801/http://www.baseball-reference.com/leagues/split.cgi?t=b&lg=MLB&year=2012#plato |archive-date=9 September 2015 |url-status=live }}</ref> Because there are fewer left-handed pitchers than right-handed pitchers, left-handed batters have more opportunities to face right-handed pitchers than their right-handed counterparts have against left-handed pitchers.<ref>{{cite web |url=http://www.hardballtimes.com/main/article/the-advantage-of-batting-left-handed/ | first = John | last = Walsh | name-list-style = vanc |title=The advantage of batting left-handed |publisher=hardballtimes.com |access-date=7 March 2013 |archive-url= https://web.archive.org/web/20130313221124/http://www.hardballtimes.com/main/article/the-advantage-of-batting-left-handed |archive-date=13 March 2013 |url-status=live }}</ref> Fourteen of the top twenty career batting averages in [[Major League Baseball]] history have been posted by left-handed batters.<ref>{{cite web |url=https://www.baseball-reference.com/leaders/batting_avg_career.shtml |title=Career Leaders & Records for Batting Average |website=Baseball Reference |access-date=6 March 2013 |archive-url=https://web.archive.org/web/20130413224624/http://www.baseball-reference.com/leaders/batting_avg_career.shtml |archive-date=13 April 2013 |url-status=live }}</ref> Left-handed batters have a slightly shorter run from the batter's box to first base than right-handers. This gives left-handers a slight advantage in beating throws to first base on infield ground balls.{{citation needed|date=December 2019}} ** Because a left-handed pitcher faces first base when he is in position to throw to the batter, whereas a right-handed pitcher has his back to first base, a left-handed pitcher has an advantage when attempting to [[pickoff|pick off]] baserunners at first base.<ref name="First Base Pickoffs for Lefty Pitchers">{{cite web |url=http://baseball.isport.com/baseball-guides/first-base-pickoffs-for-lefty-pitchers |title=First Base Pickoffs for Lefty Pitchers |publisher=isport.com |access-date=7 March 2013 |archive-url=https://web.archive.org/web/20130622212223/http://baseball.isport.com/baseball-guides/first-base-pickoffs-for-lefty-pitchers |archive-date=22 June 2013 |url-status=dead }}</ref> ** Defensively in baseball, left-handedness is considered an advantage for [[first basemen]] because they are better suited to fielding balls hit in the gap between first and second base, and because they do not have to pivot their body around before throwing the ball to another [[infielder]].<ref>{{cite news |url=https://www.nytimes.com/2009/03/29/sports/baseball/29score.html?_r=0 | last = Miller | first = Stuart | name-list-style = vanc |title=The Decline of Left-Handed First Basemen |newspaper=nytimes.com |access-date=7 March 2013 |date=29 March 2009 |archive-url=https://web.archive.org/web/20150926170156/http://www.nytimes.com/2009/03/29/sports/baseball/29score.html?_r=0 |archive-date=26 September 2015 |url-status=live }}</ref> For the same reason, the other infielder's positions are seen as being advantageous to right-handed throwers. Historically, there have been few left-handed catchers because of the perceived disadvantage a left-handed catcher would have in making the throw to third base, especially with a right-handed hitter at the plate.<ref name="Left Handed Catchers">{{cite web |url=http://bb_catchers.tripod.com/catchers/catchleft.htm |title=Left Handed Catchers |publisher=The Encyclopedia of Baseball Catchers |access-date=7 March 2013 |archive-url=https://web.archive.org/web/20120817090402/http://bb_catchers.tripod.com/catchers/catchleft.htm |archive-date=17 August 2012 |url-status=live }}</ref> A left-handed catcher would have a potentially more dangerous time tagging out a [[baserunner]] trying to score.<ref name="Left Handed Catchers"/> With the ball in the glove on the right hand, a left-handed catcher would have to turn his body to the left to tag a runner. In doing so, he can lose the opportunity to brace himself for an impending collision.<ref name="Left Handed Catchers"/> On the other hand, the Encyclopedia of Baseball Catchers states:<ref name="Left Handed Catchers"/> {{Quote |text=One advantage is a left-handed catcher's ability to frame a right-handed pitcher's breaking balls. A right-handed catcher catches a right-hander's [[breaking ball]] across his body, with his glove moving out of the strike zone. A left-handed catcher would be able to catch the pitch moving into the strike zone and create a better target for the umpire.}} * In [[four wall handball]], typical strategy is to play along the left wall forcing the opponent to use their left hand to counter the attack and playing into the strength of a left-handed competitor. * In [[handball]], left-handed players have an advantage on the right side of the field when attacking, getting a better angle, and that defenders might be unused to them. Since few people are left-handed, there is a demand for such players. * In [[water polo]], the centre forward position has an advantage in turning to shoot on net when rotating the reverse direction as expected by the centre of the opposition defence and gain an improved position to score. Left-handed drivers are usually on the right side of the field, because they can get better angles to pass the ball or shoot for goal. * [[Ice hockey]] typically uses a strategy in which a [[defenceman (ice hockey)|defence pairing]] includes one left-handed and one right-handed defender. A disproportionately large number of ice hockey players of all positions, 62 percent, shoot left, though this does not necessarily indicate left-handedness.<ref>{{cite news|url=http://www.buffalohockeybeat.com/depleted-sabres-defense-thrives/|title=Depleted Sabres defense thrives|last=Hoppe|first=Bill| name-list-style = vanc |work=Buffalo Hockey Beat|publisher=Olean Times Herald|date=January 23, 2017|access-date=January 23, 2017|archive-url=https://web.archive.org/web/20181216031952/http://www.buffalohockeybeat.com/depleted-sabres-defense-thrives/|archive-date=December 16, 2018|url-status=live}}</ref> * In [[American football]], the handedness of a [[quarterback]] affects blocking patterns on the [[offensive line]]. [[Tight end]]s, when only one is used, typically line up on the same side as the throwing hand of the quarterback, while the [[offensive tackle]] on the opposite hand, which protects the quarterback's "blind side," is typically the most valued member of the offensive line. Receivers also have to adapt to the opposite spin.<ref>{{cite news |last1=Greene |first1=Nick |title=Why Left-Handed Quarterbacks Are So Rare |url=https://slate.com/culture/2020/11/tua-tagovailoa-left-handed-quarterbacks-rare-nfl.html |access-date=5 November 2020 |work=[[Slate (magazine)|Slate]] |date=2 November 2020}}</ref> While uncommon, there have been several [[List of left-handed quarterbacks|notable left-handed quarterbacks]]. * In [[bowling]], the oil pattern used on the bowling lane [[bowling ball#Effect of lane characteristics on ball motion|breaks down]] faster the more times a ball is rolled down the lane. Bowlers must continually adjust their shots to compensate for the ball's change in rotation as the game or series is played and the oil is altered from its original pattern. A left-handed bowler competes on the opposite side of the lane from the right-handed bowler and therefore deals with less breakdown of the original oil placement. This means left-handed bowlers have to adjust their shot less frequently than right-handed bowlers in team events or qualifying rounds where there are possibly 4-10 people per set of two lanes. This can allow them to stay more consistent. However, this advantage is not present in bracket rounds and tournament finals where matches are 1v1 on a pair of lanes. === Gender === According to a meta-analysis of 144 studies, totaling 1,787,629 participants, the best estimate for the male to female odds ratio was 1.23, indicating 23% more men are left-handed. 11% of men and 9% of women would be approximately 10% overall, at a 1.22 male to female odds ratio.<ref name="Papadatou">{{cite journal | vauthors = Papadatou-Pastou M, Martin M, Munafò MR, Jones GV | title = Sex differences in left-handedness: a meta-analysis of 144 studies | journal = Psychological Bulletin | volume = 134 | issue = 5 | pages = 677–699 | date = September 2008 | pmid = 18729568 | doi = 10.1037/a0012814 }}</ref>{{clarify|date=January 2018}} === Sexuality and gender identity === {{further|Handedness and sexual orientation}} A number of studies examining the relationship between handedness and sexual orientation have reported that a disproportionate minority of homosexual people exhibit left-handedness,<ref>{{cite journal | vauthors = Lalumière ML, Blanchard R, Zucker KJ | title = Sexual orientation and handedness in men and women: a meta-analysis | journal = Psychological Bulletin | volume = 126 | issue = 4 | pages = 575–92 | date = July 2000 | pmid = 10900997 | doi = 10.1037/0033-2909.126.4.575 }}</ref> though findings are mixed.<ref>{{cite journal | vauthors = Mustanski BS, Bailey JM, Kaspar S | s2cid = 29217315 | title = Dermatoglyphics, handedness, sex, and sexual orientation | journal = Archives of Sexual Behavior | volume = 31 | issue = 1 | pages = 113–22 | date = February 2002 | pmid = 11910784 | doi = 10.1023/A:1014039403752 }}</ref><ref>{{cite journal |last1=Williams |first1=Terrance J. |last2=Pepitone |first2=Michelle E. |last3=Christensen |first3=Scott E. |last4=Cooke |first4=Bradley M. |last5=Huberman |first5=Andrew D. |last6=Breedlove |first6=Nicholas J. |last7=Breedlove |first7=Tessa J. |last8=Jordan |first8=Cynthia L. |last9=Breedlove |first9=S. Marc |title=Finger-length ratios and sexual orientation |journal=Nature |date=March 2000 |volume=404 |issue=6777 |pages=455–456 |doi=10.1038/35006555 |pmid=10761903 |bibcode=2000Natur.404..455W |s2cid=205005405 }}</ref><ref>{{cite journal | vauthors = Schwartz G, Kim RM, Kolundzija AB, Rieger G, Sanders AR | s2cid = 24358057 | title = Biodemographic and physical correlates of sexual orientation in men | journal = Archives of Sexual Behavior | volume = 39 | issue = 1 | pages = 93–109 | date = February 2010 | pmid = 19387815 | doi = 10.1007/s10508-009-9499-1 }}</ref> A 2001 study also found that male children who have different [[Gender identity|gender identities]] were more than twice as likely to be left-handed than a clinical [[control group]] (19.5% vs. 8.3%, respectively).<ref>{{cite journal | vauthors = Zucker KJ, Beaulieu N, Bradley SJ, Grimshaw GM, Wilcox A | s2cid = 4987839 | title = Handedness in boys with gender identity disorder | journal = Journal of Child Psychology and Psychiatry, and Allied Disciplines | volume = 42 | issue = 6 | pages = 767–76 | date = September 2001 | pmid = 11583249 | doi = 10.1111/1469-7610.00773 }}</ref> [[Paraphilia]]s (atypical sexual interests) have also been linked to higher rates of left-handedness. A 2008 study analyzing the sexual fantasies of 200 males found "elevated paraphilic interests were correlated with elevated non-right handedness".<ref>{{cite journal | vauthors = Rahman Q, Symeonides DJ | s2cid = 22274418 | title = Neurodevelopmental correlates of paraphilic sexual interests in men | journal = Archives of Sexual Behavior | volume = 37 | issue = 1 | pages = 166–72 | date = February 2008 | pmid = 18074220 | doi = 10.1007/s10508-007-9255-3 }}</ref> Greater rates of left-handedness has also been documented among [[pedophilia|pedophiles]].<ref>{{cite journal | vauthors = Blanchard R, Kolla NJ, Cantor JM, Klassen PE, Dickey R, Kuban ME, Blak T | s2cid = 220359453 | title = IQ, handedness, and pedophilia in adult male patients stratified by referral source | journal = Sexual Abuse | volume = 19 | issue = 3 | pages = 285–309 | date = September 2007 | pmid = 17634757 | doi = 10.1177/107906320701900307 }}</ref><ref>{{cite journal | vauthors = Cantor JM, Klassen PE, Dickey R, Christensen BK, Kuban ME, Blak T, Williams NS, Blanchard R | s2cid = 6427342 | display-authors = 6 | title = Handedness in pedophilia and hebephilia | journal = Archives of Sexual Behavior | volume = 34 | issue = 4 | pages = 447–59 | date = August 2005 | pmid = 16010467 | doi = 10.1007/s10508-005-4344-7 }}</ref><ref>{{cite journal | vauthors = Bogaert AF | s2cid = 28513717 | title = Handedness, criminality, and sexual offending | journal = Neuropsychologia | volume = 39 | issue = 5 | pages = 465–9 | year = 2001 | pmid = 11254928 | doi = 10.1016/S0028-3932(00)00134-2 }}</ref><ref>{{cite journal | vauthors = Dyshniku F, Murray ME, Fazio RL, Lykins AD, Cantor JM | s2cid = 25667170 | title = Minor Physical Anomalies as a Window into the Prenatal Origins of Pedophilia | journal = Archives of Sexual Behavior | volume = 44 | issue = 8 | pages = 2151–9 | date = November 2015 | pmid = 26058490 | doi = 10.1007/s10508-015-0564-7 }}</ref> A 2014 study attempting to analyze the biological markers of [[asexuality]] asserts that non-sexual men and women were 2.4 and 2.5 times, respectively, more likely to be left-handed than their heterosexual counterparts.<ref name=Yule>{{cite journal | vauthors = Yule MA, Brotto LA, Gorzalka BB | s2cid = 5347734 | title = Biological markers of asexuality: Handedness, birth order, and finger length ratios in self-identified asexual men and women | journal = Archives of Sexual Behavior | volume = 43 | issue = 2 | pages = 299–310 | date = February 2014 | pmid = 24045903 | doi = 10.1007/s10508-013-0175-0 }}</ref> === Mortality rates in combat === A study at [[Durham University]] — which examined mortality data for [[cricketers]] whose handedness was a matter of public record — found that left-handed men were almost twice as likely to die in war as their right-handed contemporaries.<ref>{{cite journal | vauthors = Aggleton JP, Kentridge RW, Neave NJ | title = Evidence for longevity differences between left handed and right handed men: an archival study of cricketers | journal = Journal of Epidemiology and Community Health | volume = 47 | issue = 3 | pages = 206–9 | date = June 1993 | pmid = 8350033 | pmc = 1059767 | doi = 10.1136/jech.47.3.206 }}</ref> The study theorised that this was because weapons and other equipment was designed for the right-handed. “I can sympathise with all those left-handed cricketers who have gone to an early grave trying desperately to shoot straight with a right-handed Lee Enfield .303,” wrote a journalist reviewing the study in the cricket press.<ref>{{Cite journal|last=Jonathan|first=Rice| name-list-style = vanc |date=February 1995|title=Left For Dead|journal=Wisden Cricket Monthly}}</ref> The findings echo those of previous American studies, which found that left-handed US sailors were 34% more likely to have a serious accident than their right-handed counterparts.<ref>{{cite web |url= https://www.newscientist.com/article/mg14119163-000-science-sudden-death-for-left-handers/ |title=Science: Sudden death for left-handers|last= Brown |first = William | name-list-style = vanc |website=New Scientist|language=en-US|access-date=2020-02-01}}</ref> === Episodic memory etc=== A high level of handedness is associated with poorer [[episodic memory]],<ref>{{cite journal | vauthors = Propper RE, Christman SD, Phaneuf KA | s2cid = 2989930 | title = A mixed-handed advantage in episodic memory: a possible role of interhemispheric interaction | journal = Memory & Cognition | volume = 33 | issue = 4 | pages = 751–7 | date = June 2005 | pmid = 16248339 | doi = 10.3758/BF03195341 }}</ref><ref>{{cite journal | vauthors = Sahu A, Christman SD, Propper RE | title = The contributions of handedness and working memory to episodic memory | journal = Memory & Cognition | volume = 44 | issue = 8 | pages = 1149–1156 | date = November 2016 | pmid = 27259533 | doi = 10.3758/s13421-016-0625-8 | doi-access = free }}</ref> and with poorer communication between brain hemispheres,<ref>{{cite journal | vauthors = Prichard E, Propper RE, Christman SD | title = Degree of Handedness, but not Direction, is a Systematic Predictor of Cognitive Performance | language = en | journal = Frontiers in Psychology | volume = 4 | pages = 9 | date = 2013 | pmid = 23386836 | doi = 10.3389/fpsyg.2013.00009 | pmc = 3560368 }}</ref> which may give poorer emotional processing, although [[bilateral stimulation]] may reduce such effects.<ref>{{cite journal | vauthors = Shobe ER | title = Independent and collaborative contributions of the cerebral hemispheres to emotional processing | journal = Frontiers in Human Neuroscience | volume = 8 | pages = 230 | date = 2014-04-22 | pmid = 24795597 | pmc = 4001044 | doi = 10.3389/fnhum.2014.00230 }}</ref><ref>{{cite journal | vauthors = Spielberg JM, Heller W, Miller GA | title = Hierarchical brain networks active in approach and avoidance goal pursuit | journal = Frontiers in Human Neuroscience | volume = 7 | pages = 284 | date = 2013-06-17 | pmid = 23785328 | pmc = 3684100 | doi = 10.3389/fnhum.2013.00284 }}</ref> === Corpus callosum === A high level of handedness is associated with a smaller [[corpus callosum]] whereas low handedness with a larger one.<ref>{{cite journal |last1=Luders |first1=Eileen |last2=Cherbuin |first2=Nicolas |last3=Thompson |first3=Paul M. |last4=Gutman |first4=Boris |last5=Anstey |first5=Kaarin J. |last6=Sachdev |first6=Perminder |last7=Toga |first7=Arthur W. |title=When more is less: Associations between corpus callosum size and handedness lateralization |journal=NeuroImage |date=August 2010 |volume=52 |issue=1 |pages=43–49 |doi=10.1016/j.neuroimage.2010.04.016 |pmid=20394828 |pmc=2903194 }}</ref> == In culture == {{Main|Bias against left-handed people}} Many tools and procedures are designed to facilitate use by right-handed people, often without realizing the difficulties incurred by the left-handed. John W. Santrock has written, "For centuries, left-handers have suffered unfair discrimination in a world designed for right-handers."<ref name=":2">{{cite book | last = Santrock | first = John W. | date = 2008 | title = Motor, Sensory, and Perceptual Development | veditors = Ryan M | chapter = A Topical Approach to Life-Span Development | pages = 172–205 | location = Boston, MA | publisher = McGraw-Hill Higher Education }}</ref> As a child British King [[George VI]] (1895-1952) was naturally left-handed. He was forced to write with his right hand, as was common practice at the time. He was not expected to become king, so that was not a factor.<ref>{{cite journal |last1=Kushner |first1=Howard I |title=Retraining the King's left hand |journal=The Lancet |date=June 2011 |volume=377 |issue=9782 |pages=1998–1999 |doi=10.1016/s0140-6736(11)60854-4 |pmid=21671515 |s2cid=35750495 }}</ref> McManus noted that, as the [[Industrial Revolution]] spread across Western Europe and the United States in the 19th century, workers needed to operate complex machines that were designed with right-handers in mind. This would have made left-handers more visible and at the same time appear less capable and more clumsy. During this era, children were taught to write with a [[dip pen]]. While a right-hander could smoothly drag the pen across paper from left to right, a dip pen could not easily be pushed across by the left hand without digging into the paper and making blots and stains.<ref>{{cite book |doi=10.1017/CBO9780511576744.004 |chapter=The history and geography of human handedness |title=Language Lateralization and Psychosis |year=2009 |last1=McManus |first1=I. C. |pages=37–58 |isbn=978-0-511-57674-4 |editor2-first=Rene S |editor2-last=Kahn |editor1-first=Iris E. C |editor1-last=Sommer }}</ref> ===Negative connotations and discrimination=== Moreover, apart from inconvenience, left-handed people have historically been considered unlucky or even malicious for their difference by the right-handed majority. In many European languages, including English, the word for the direction "right" also means "correct" or "proper". Throughout history, being left-handed was considered negative, or evil; even into the 20th century, left-handed children were beaten by schoolteachers for writing with their left hand. The Latin adjective ''sinister'' or ''sinistra'' (as applied to male or female nouns ⁠— ⁠Latin nouns are gender specific) means "left" as well as "unlucky", and this double meaning survives in European derivatives of Latin, including the English words "sinister" (meaning both 'evil' and 'on the bearer's left on a coat of arms') and "ambisinister" meaning 'awkward or clumsy with both or either hand'. There are many negative connotations associated with the phrase "left-handed": clumsy, awkward, unlucky, insincere, sinister, malicious, and so on. A "left-handed compliment" is one that has two meanings, one of which is unflattering to the recipient. In [[French language|French]], ''gauche'' means both "left" and "awkward" or "clumsy", while ''droit(e)'' ([[cognate]] to English ''direct'' and related to "adroit") means both "right" and "straight", as well as "law" and the legal sense of "right". The name "Dexter" derives from the Latin for "right", as does the word "dexterity" meaning manual skill. As these are all very old words, they would tend to support theories indicating that the predominance of right-handedness is an extremely old phenomenon. [[Black magic]] is sometimes referred to as the "[[left-hand path]]". Until very recently in [[Taiwan]] (and still in [[Mainland China]], [[Japan]] and [[Korea|both North and South Korea]]), left-handed people were forced to switch to being right-handed, or at least switch to writing with the right hand. Due to the importance of [[stroke order]], developed for the comfortable use of right-handed people, it is considered more difficult to write legible Chinese characters with the left hand than it is to write Latin letters, though difficulty is subjective and depends on the writer.<ref>{{cite web|url=http://www.china.org.cn/english/LivinginChina/243637.htm|title=A question of the left being right – and normal|work=China Daily|date=February 22, 2008|access-date=2011-01-19| archive-url= https://web.archive.org/web/20110124025533/http://china.org.cn/english/LivinginChina/243637.htm| archive-date= January 24, 2011 | url-status= live}}</ref> Because writing when moving one's hand away from its side towards the other side of the body can cause smudging if the outward side of the hand is allowed to drag across the writing, writing in the [[Latin alphabet]] might possibly be less feasible with the left hand than the right under certain circumstances. Conversely, right-to-left alphabets, such as the Arabic and Hebrew, are generally considered easier to write with the left hand in general.{{citation needed|date=September 2013}} Depending on the position and inclination of the writing paper, and the writing method, the left-handed writer can write as neatly and efficiently or as messily and slowly as right-handed writers. Usually the left-handed child needs to be taught how to write correctly with the left hand, since discovering a comfortable left-handed writing method on one's own may not be straightforward.<ref>{{cite web | url = http://www.lefthander-consulting.org/deutsch/InfoSchreiben.htm | title = Erste deutsche Beratungs- und Informationsstelle für Linkshänder und umge-schulte Linkshänder | language = de | archive-url = https://web.archive.org/web/20130922143207/http://www.lefthander-consulting.org/deutsch/InfoSchreiben.htm | archive-date = 2013-09-22 | work = lefthander-consulting.org | access-date = 21 September 2013 }}</ref><ref>{{cite web | url = http://handedness.org/action/leftwrite.html | work = Handedness Research Institute | title = Teaching Left-Handers to Write | archive-url = https://web.archive.org/web/20130923084340/http://handedness.org/action/leftwrite.html | archive-date=2013-09-23 | access-date = 21 September 2013 }}</ref> In the Soviet Union, all left-handed children were forced to write with their right hand in the Soviet school system.<ref>А. П. Чуприков, В. Д. Мишиев. // Латеральность населения СССР в конце 70-х и начале 80-х годов. К истории латеральной нейропсихологии и нейропсихиатрии. Хрестоматия. Донецк, 2010, 192 с.</ref><ref name=autogenerated2>А. П. Чуприков, Е. А. Волков. // Мир леворуких. Киев. 2008.</ref> === International Left-Handers Day === {{main|International Left-Handers Day}} International Left-Handers Day is held annually every August 13.<ref name="about">{{cite web | url = http://www.lefthandersday.com/about.html | title = Left-Handers' Day August 13th: Celebrate your right to be left-handed | archive-url = https://web.archive.org/web/20140715131212/http://www.lefthandersday.com/about.html | archive-date=2014-07-15 | work = lefthandersday.com | access-date = 12 August 2013 }}</ref> It was founded by the Left-Handers Club in 1992, with the club itself having been founded in 1990.<ref name="about" /> International Left-Handers Day is, according to the club, "an annual event when left-handers everywhere can celebrate their sinistrality (left-handedness) and increase public awareness of the advantages and disadvantages of being left-handed."<ref name="about" /> It celebrates their uniqueness and differences, who are from seven to ten percent of the world's population. Thousands of left-handed people in today's society have to adapt to use right-handed tools and objects. Again according to the club, "in the U.K. alone there were over 20 regional events to mark the day in 2001 – including left-v-right sports matches, a left-handed tea party, pubs using left-handed corkscrews where patrons drank and played pub games with the left hand only, and nationwide 'Lefty Zones' where left-handers' creativity, adaptability and sporting prowess were celebrated, whilst right-handers were encouraged to try out everyday left-handed objects to see just how awkward it can feel using the wrong equipment!"<ref name="about" /> == In other animals == [[Kangaroo]]s and other [[Macropodidae|macropod]] [[marsupial]]s show a left-hand preference for everyday tasks in the wild. 'True' handedness is unexpected in marsupials however, because unlike [[Placentalia|placental mammals]], they lack a [[corpus callosum]]. Left-handedness was particularly apparent in the red kangaroo (''Macropus rufus'') and the eastern gray kangaroo (''Macropus giganteus''). Red-necked (Bennett's) wallabies (''Macropus rufogriseus'') preferentially use their left hand for behaviours that involve fine manipulation, but the right for behaviours that require more physical strength. There was less evidence for handedness in [[arboreal]] species.<ref name="Sci-News">{{cite web |date=June 18, 2015 |title=All kangaroos are lefties, scientists say |website=Sci-News.com |url=http://www.sci-news.com/biology/science-kangaroos-lefties-02929.html |access-date=June 19, 2015 |archive-url=https://web.archive.org/web/20150619200055/http://www.sci-news.com/biology/science-kangaroos-lefties-02929.html |archive-date=June 19, 2015 |url-status=live }}</ref> Studies of dogs, horses, and domestic cats have shown that females of those species tend to be right-handed, while males tend to be left-handed.<ref>{{cite web |last=Callaway |first=Ewen | name-list-style = vanc |date=24 July 2009 |title=Is your cat left or right pawed? |website=New Scientist |url=https://www.newscientist.com/article/dn17510-is-your-cat-left-or-right-pawed/ |access-date=6 November 2016 |archive-url=https://web.archive.org/web/20161107014511/https://www.newscientist.com/article/dn17510-is-your-cat-left-or-right-pawed/ |archive-date=7 November 2016 |url-status=live }}</ref> == See also == ===General=== * [[Cardinal direction]] * [[Clockwise]], which also discusses counterclockwise/anticlockwise, the two terms for the opposite sense of rotation * [[Dexter and sinister]] * [[Footedness]] * [[Laterality]] * [[Left- and right-hand traffic]] * [[Ocular dominance]] (eyedness) * [[Proper right and proper left]] * [[Relative direction]] ===Handedness=== * [[Edinburgh Handedness Inventory]] * [[Geschwind–Galaburda hypothesis]] * [[Neuroanatomy of handedness]] * [[Situs inversus]] * [[Twins and handedness]] == References ==<!-- CurrAnthropol40:90. --> {{Reflist}} == External links == {{Wiktionary}} {{Commons category|Left-handedness}} * [https://www.sciencedaily.com/releases/2006/04/060414010532.htm Lefties Have The Advantage In Adversarial Situations], ScienceDaily, April 14, 2006. * [http://www.scq.ubc.ca/?p=74 Science Creative Quarterly's overview of some of the genetic underpinnings of left-handedness] * [http://www.commonties.com/blog/2006/09/13/i-was-a-rebel/ A left-handed senior citizen recalls the emotional torment he faced at a New York public school in the 1920s.] (Audio slideshow) * Woznicki, Katrina (2005). [http://www.medpagetoday.com/HematologyOncology/BreastCancer/1810 "Breast Cancer Risk Doubles for Southpaw Women"], MedPage Today, 26 September. * Hansard (1998) '[https://publications.parliament.uk/pa/cm199798/cmhansrd/vo980722/debtext/80722-15.htm Left-handed Children]', Debate contribution by the Rt Hon. Mr. Peter Luff (MP for Mid-Worcestershire), House of Commons, 22 July. * {{cite book | title = Is your Child Left-Handed? Why, according to psychological tests, left-handed people ought to remain so | url = https://books.google.com/books?id=EikDAAAAMBAJ&pg=PA22 | publisher = [[Popular Science]] | date = December 1918 | page = 22 }} * [http://papers.nber.org/papers/w12387.pdf Handedness and Earnings] / [https://web.archive.org/web/20070314134323/http://blogs.reuters.com/2006/08/11/higher-paychecks-a-left-handed-compliment/ Higher paychecks: a left-handed compliment?] * [https://web.archive.org/web/20090324225537/http://www.ucd.ie/geary/publications/2004/laterality.pdf Handedness & earnings, published in Journal of Human Resources 2007] * [http://handedness.org/ Handedness Research Institute] * [http://www.livescience.com/19968-study-reveals-lefties-rare.html Study Reveals Why Lefties Are Rare] {{Handedness}} {{Laterality}} [[Category:Handedness| ]] [[Category:Chirality]] [[Category:Discrimination]] [[Category:Mental processes]] [[Category:Asymmetry]] [[ca:Dretà]]'