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In
human biology Human biology is an interdisciplinary area of academic study that examines humans through the influences and interplay of many diverse fields such as human genetics, genetics, human evolution, evolution, human physiology, physiology, anatomy, epidem ...
, handedness is an individual's preferential use of one
hand A hand is a prehensile, multi- fingered appendage located at the end of the forearm The forearm is the region of the upper limb between the Elbow-joint, elbow and the wrist. The term forearm is used in anatomy to distinguish it from the arm, ...

hand
, known as the dominant hand, due to it being stronger, faster or better in
dexterity Fine motor skill (or dexterity) is the coordination of small muscles in movement with the eyes, usually involving the synchronisation of hands and fingers. The complex levels of manual dexterity that humans exhibit can be attributed to and demon ...
. The other hand, comparatively often the weaker, less dextrous or simply less subjectively preferred, is called the non-dominant hand. Right-handedness is by far more common; about 90% of the human population are right hand dominant. 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 Ambidexterity is the ability to use both the right and left hand equally well. When referring to objects, the term indicates that the object is equally suitable for right-handed and left-handed people. When referring to humans, it indicates that a ...
(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 In biology, epigenetics is the study of heritability, heritable phenotype changes that do not involve alterations in the DNA sequence. The Ancient Greek, Greek prefix ''wikt:epi-, epi-'' ( "over, outside of, around") in ''epigenetics'' implies f ...
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. 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 Sport pertains to any form of competitive Competition is a rivalry A rivalry is the state of two people or groups engaging in a lasting competitive relationship. Rivalry is the "against each other" spirit between two competing sides. ...

sport
s that involves aiming at a target in an area of an opponent's control, as their opponents are more accustomed to the right-handed majority. As a result, they are over-represented in
baseball Baseball is a bat-and-ball games, bat-and-ball game played between two opposing teams who take turns batting (baseball), batting and fielding. The game proceeds when a player on the fielding team (baseball), fielding team, called the pi ...

baseball
,
tennis Tennis is a racket sport that can be played individually against a single opponent (Types of tennis match#Singles, singles) or between two teams of two players each (Types of tennis match#Doubles, doubles). Each player uses a tennis racket th ...

tennis
,
fencing Fencing is a group of three related combat sports. The three disciplines in modern fencing are the foil (fencing), foil, the épée, and the sabre (fencing), sabre (also ''saber''); winning points are made through the weapon's contact with an ...

fencing
,
cricket Cricket is a bat-and-ball gameBat-and-ball may refer to: *Bat-and-ball games Bat-and-ball games (or safe haven games) are field games played by two opposing teams, in which the action starts when the defending team throws a ball at a ded ...

cricket
,
boxing Boxing is a in which two people, usually wearing and other protective equipment such as hand wraps and mouthguards, throw at each other for a predetermined amount of time in a . is both an and sport and is a standard fixture in most inte ...

boxing
and .


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. * ''Left-handedness'' is far less common than right-handedness. Studies suggest that approximately 10% of people are left-handed. *''Mixed-handedness'' or ''
cross-dominance Cross-dominance, also known as mixed-handedness, hand confusion, or mixed dominance, is a motor skill manifestation in which a person favors one hand for some tasks and the other hand for others, or a hand and the contralateral leg. For example, a ...
'' is the change of hand preference between different tasks. This is very uncommon in the population with about a 1% prevalence. * ''
Ambidexterity Ambidexterity is the ability to use both the right and left hand equally well. When referring to objects, the term indicates that the object is equally suitable for right-handed and left-handed people. When referring to humans, it indicates that a ...
'' refers to having equal ability in both hands. Those who learn it still tend to favor their originally dominant hand. This is very uncommon, with about a 1% prevalence.


Measurement

Handedness may be measured behaviourally (performance measures) or through questionnaires (preference measures). The
Edinburgh Handedness Inventory The Edinburgh Handedness Inventory is a measurement scale used to assess the dominance of a person's right or left hand in everyday activities, sometimes referred to as laterality The term laterality refers to the preference most humans Hu ...
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.


Causes

There are several theories of how handedness develops. Occurrences during
prenatal development Prenatal development () includes the development of the embryo and of the foetus during a viviparous animal's gestation. Prenatal development starts with fertilization , in the germinal stage of embryonic development, and continues in fetal d ...

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. In a 2013 study, 39% of infants (6 to 14 months) and 97% of toddlers (18 to 24 months) demonstrated a hand preference.


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 implies that left-handed people have a reversed organisation. However, this theory does not address the fact that the majority of left-handers have left-hemisphere language dominance—just like right-handers. 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. Others have more ambiguous bilateral organisation, where both hemispheres do parts of typically lateralised functions. When tasks investigating lateralisation 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. This finding is likely due to the small proportion of left-handers who have atypical brain organisation.


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. A large study of twins from 25,732 families by Medland et al. (2006) indicates that the
heritability Heritability is a used in the fields of and that estimates the degree of ''variation'' in a in a that is due to between individuals in that population. It measures how much of the variation of a trait can be attributed to variation of geneti ...

heritability
of handedness is roughly 24%. Two theoretical single-gene models have been proposed to explain the patterns of inheritance of handedness, by Marian Annett of the
University of Leicester , mottoeng = So that they may have life , established = 1921 – Leicestershire and Rutland University College1957 – gained Universities in the United Kingdom, university status by royal charter , type = public university, Public , endowment ...
, and by Chris McManus of UCL. However, growing evidence from
linkage Linkage may refer to: *Linkage (album), ''Linkage'' (album), by J-pop singer Mami Kawada, released in 2010 *Linkage (graph theory), the maximum min-degree of any of its subgraphs *Linkage (horse), an American Thoroughbred racehorse *Hierarchical cl ...
and genome-wide association studies suggests that genetic variance in handedness cannot be explained by a single genetic
locus Locus (plural loci) is Latin for "place". It may refer to: Entertainment * Locus (comics), a Marvel Comics mutant villainess, a member of the Mutant Liberation Front * Locus (magazine), ''Locus'' (magazine), science fiction and fantasy magazine ...
. From these studies, McManus et al. now conclude that handedness is
polygenicA polygene is a member of a group of non-epistatic gene In biology, a gene (from ''genos'' "...Wilhelm Johannsen coined the word gene to describe the Mendelian_inheritance#History, Mendelian units of heredity..." (Greek language, Greek) meani ...
and estimate that at least 40
loci Locus (plural loci) is Latin for "place". It may refer to: Entertainment * Locus (comics), a Marvel Comics mutant villainess, a member of the Mutant Liberation Front * Locus (magazine), ''Locus'' (magazine), science fiction and fantasy magazine ...
contribute to the trait. Brandler et al. performed a
genome-wide association study In genetics Genetics is a branch of biology concerned with the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) Though heredity had been observed for millennia, Gregor Mendel, Moravia, Moravian scientist a ...
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. Brandler and Paracchini suggest the same mechanisms that determine left/right asymmetry in the body (e.g.
nodal signaling The nodal signaling pathway is a signal transduction pathway important in regional differentiation, regional and cellular differentiation during embryonic development. The NODAL, nodal family of proteins, a subset of the TGF beta signaling pathwa ...

nodal signaling
and
ciliogenesis Ciliogenesis is defined as the building of the cell's antenna (primary cilium, primary cilia) or extracellular fluid mediation mechanism (motile cilia, motile cilium). It includes the assembly and disassembly of the cilia during the cell cycle. ...
) also play a role in the development of brain asymmetry (handedness being a reflection of brain asymmetry for motor function). 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.


Epigenetic factors

Twin studies Twin studies are studies conducted on Identical twin, identical or Fraternal twin, fraternal twins. They aim to reveal the importance of environmental and genetics, genetic influences for traits, phenotypes, and disorders. Twin research is conside ...
indicate that genetic factors explain 25% of the variance in handedness, and environmental factors the remaining 75%. While the molecular basis of handedness
epigenetics In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechani ...
is largely unclear, Ocklenburg et al. (2017) found that asymmetric
methylation In the chemical sciences, methylation denotes the addition of a methyl group A methyl group is an alkyl derived from methane, containing one carbon atom chemical bond, bonded to three hydrogen atoms — CH3. In chemical formula, fo ...

methylation
of
CpG site The CpG sites or CG sites are regions of DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon ...
s plays a key role for
gene expression Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product that enables it to produce end products, protein or non-coding RNA, and ultimately affect a phenotype, as the final effect. The ...

gene expression
asymmetries related to handedness.


Prenatal hormone exposure

Four studies have indicated that individuals who have had in-utero exposure to
diethylstilbestrol Diethylstilbestrol (DES), also known as stilbestrol or stilboestrol, is a nonsteroidal estrogen medication, which is presently rarely used. In the past, it was widely used for a variety of indications, including pregnancy support for women with a ...

diethylstilbestrol
(a synthetic
estrogen Estrogens or oestrogens, are a class of natural or synthetic s responsible for the development and regulation of the female and s. There are three major estrogens that have estrogenic hormonal activity: (E1), (E2), and (E3). Estradiol, an ...

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".


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 The occipital bone () is a cranial dermal bone and the main bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the vertebrate skeleton in animals. Bones protect the various organs of the body, produce red bl ...
(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 The Vestibular (from pt, vestíbulo, "entrance hall") is a competitive examination and is the primary and widespread entrance system used by Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the ...
abnormalities or delay, and asymmetry of the is strongly correlated with the direction of handedness.


Ultrasound

Another theory is that
ultrasound Ultrasound is sound wave In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, ...
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 ultrasound screening (sonography used to check the healthy development of the fetus and mother) and left-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. 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. Scharoun and Bryden noted that right-handed preference increases with age up to the teenage years.


Correlation with other factors


Intelligence

In his book ''Right-Hand, Left-Hand'', Chris McManus of
University College London University College London, which Trade name, operates as UCL, is a major public university , public research university located in London, United Kingdom. UCL is a Member institutions of the University of London, member institution of the Federa ...
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. Writing in ''
Scientific American ''Scientific American'' (informally abbreviated ''SciAm'' or sometimes ''SA'') is an American popular science Popular science (also called pop-science or popsci) is an interpretation of science Science (from the Latin word ''scientia'', ...
'', he states:
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.
Conversely, Joshua Goodman found that evidence for left-handers was overrepresented amongst those with higher cognitive skills, such as
Mensa Mensa may refer to: *Mensa International Mensa is the largest and oldest high IQ society in the world. It is a non-profit organization open to people who score at the 98th percentile In statistics Statistics is the discipline that conce ...
members and higher-performing takers of and
MCAT The Medical College Admission Test (MCAT) is a computer-based standardized examination for prospective medical students A medical school is a tertiary educational institution, or part of such an institution, that teaches medicine, and awar ...
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 Intellectual disability (ID), also known as general learning disability and formerly mental retardation (MR),Rosa's Law, Pub. L. 111-256124 Stat. 2643(2010). is a generalized neurodevelopmental disorder characterized by significantly impaired in ...
(ID) being roughly twice as likely to be left-handed, as well as generally lower cognitive and non-cognitive abilities amongst left-handed children. 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). The prevalence of ''difficulties'' in left-right discrimination was investigated in a cohort of 2,720 adult members of
Mensa Mensa may refer to: *Mensa International Mensa is the largest and oldest high IQ society in the world. It is a non-profit organization open to people who score at the 98th percentile In statistics Statistics is the discipline that conce ...
and
Intertel Intertel (previously the International Legion of Intelligence) is a high IQ society, high-IQ society founded in 1966, that is open to those who have scored at or above the 99th percentile (top 1%) on one of various standardized tests of intellige ...
by Storfer. According to the study, 7.2% of the men and 18.8% of the women evaluated their left-right directional sense as poor or below average; moreover participants who were relatively ambidextrous experienced problems more frequently than did those who were more strongly left- or right-handed. The study also revealed an effect of age, with younger participants reporting more problems.


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. The researchers used Bayley scales of infant and toddler development to assess all the subjects.


Music

In two studies,
Diana Deutsch Diana Deutsch (born February 15, 1938) is a British-American psychologist A psychologist is a person who studies normal and abnormal mental states, perceptual, cognitive, emotional, and social processes and behavior by experimenting with, an ...
found that left-handers, particularly those with mixed hand preference, performed significantly better than right-handers in musical memory tasks. 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 octave illusion is an auditory illusion discovered by Diana Deutsch in 1973. It is produced when two tones that are an octave apart are repeatedly played in alternation ("high-low-high-low") through stereo headphones. The same sequence is p ...
, the
scale illusion Deutsch's scale illusion is an auditory illusion in which two series of unconnected notes appear to combine into a single recognisable melody, when played simultaneously into the left and right ears of a listener. The illusion is produced by simul ...
, and the
glissando illusionThe glissando illusion is an auditory illusion, created when a sound with a fixed pitch, such as a synthesized oboe tone, is played together with a sine wave A sine wave or sinusoid is a curve, mathematical curve that describes a smooth periodi ...
.


Health

Left-handed people are 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. A variety of neuropsychiatric and developmental disorders like
autism spectrum The autism spectrum encompasses a range of neurodevelopmental conditions, including autism Autism is a neurodevelopmental disorder Neurodevelopmental disorders are a group of disorders that affect the development of the nervous sys ...
disorders,
depression Depression may refer to: Mental health * Depression (mood), a state of low mood and aversion to activity * Mood disorders characterized by depression are commonly referred to as simply ''depression'', including: ** Dysthymia ** Major depressive ...
,
bipolar disorder Bipolar disorder, previously known as manic depression, is a mental disorder A mental disorder, also called a mental illness or psychiatric disorder, is a behavioral or mental pattern that causes significant distress or impairment of ...

bipolar disorder
,
anxiety disorders Anxiety disorders are a cluster of mental disorder A mental disorder, also called a mental illness or psychiatric disorder, is a behavioral or mental pattern that causes significant distress or impairment of personal functioning. Such featu ...
,
schizophrenia Schizophrenia is a mental disorder A mental disorder, also called a mental illness or psychiatric disorder, is a behavioral or mental pattern that causes significant distress or impairment of personal functioning. Such features may b ...

schizophrenia
, and
alcoholism Alcoholism is, broadly, any drinking of alcohol In , alcohol is an that carries at least one (−OH) bound to a atom. The term alcohol originally referred to the primary alcohol (ethyl alcohol), which is and is the main alcoho ...
has been associated with left- and mixed-handedness. A 2012 study showed that nearly 40% of children with
cerebral palsy Cerebral palsy (CP) is a group of movement disorders Movement disorder refers to any clinical syndrome with either an excess of movement or a paucity of voluntary and involuntary movements, unrelated to weakness or spasticity Spasticity () is ...

cerebral palsy
were left-handed, while another study demonstrated that left-handedness was associated with a 62% increased risk of
Parkinson's disease Parkinson's disease (PD), or simply Parkinson's, is a chronic condition, long-term neurodegeneration, degenerative disorder of the central nervous system that mainly affects the motor system. The symptoms usually emerge slowly, and as the disea ...
in women, but not in men. Another study suggests that the risk of developing
multiple sclerosis Multiple sclerosis (MS), also known as encephalomyelitis disseminata, is the most common demyelinating disease, in which the Myelin, insulating covers of nerve cells in the Human brain, brain and spinal cord are damaged. This damage disrupts the ...
increases for left-handed women, but the effect is unknown for men at this point. Left-handed women have a higher risk of
breast cancer Breast cancer is cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumor A benign tumor is a mass of cells Cell most o ...

breast cancer
than right-handed women and the effect is greater in post-menopausal women. At least one study maintains that left-handers are more likely to suffer from
heart disease Cardiovascular disease (CVD) is a class of diseases that involve the heart or blood vessels. CVD includes coronary artery diseases (CAD) such as angina pectoris, angina and myocardial infarction (commonly known as a heart attack). Other CVDs inc ...
, and are more likely to have reduced longevity from
cardiovascular The circulatory system, also called the cardiovascular system or the vascular system, is an organ system An organ system is a group of organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many o ...
causes. Left-handers are more likely to suffer bone fractures. One
systematic review Systematic reviews are a type of Literature review, review that uses repeatable analytical methods to collect secondary data and analyse it. Systematic reviews are a type of evidence synthesis which formulate research questions that are broad or ...
concluded: "Left-handers showed no systematic tendency to suffer from disorders of the immune system". 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.


Income

In a 2006 U.S. study, researchers from
Lafayette College Lafayette College is a private liberal arts college based in Easton, Pennsylvania Easton is a city in and the county seat of Northampton County, Pennsylvania, United States. The city's population was 26,800 as of the 2010 census. Easton is l ...
and
Johns Hopkins University The Johns Hopkins University (Johns Hopkins, Hopkins, or JHU) is a private Private or privates may refer to: Music * "In Private "In Private" was the third single in a row to be a charting success for United Kingdom, British singer Dusty S ...

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. However, more recently, in a 2014 study published by the
National Bureau of Economic Research The National Bureau of Economic Research (NBER) is an American private nonprofit A nonprofit organization (NPO), also known as a non-business entity, not-for-profit organization, or nonprofit institution, is a legal entity organized and op ...
,
Harvard Harvard University is a private Private or privates may refer to: Music * "In Private "In Private" was the third single in a row to be a charting success for United Kingdom, British singer Dusty Springfield, after an absence of nearly t ...

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.


Left-handedness and sports

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 Fencing is a group of three related combat sports. The three disciplines in modern fencing are the foil (fencing), foil, the épée, and the sabre (fencing), sabre (also ''saber''); winning points are made through the weapon's contact with an ...

fencing
, about half the participants are left-handed. The term ''southpaw'' is sometimes used to refer to a left-handed individual, especially in
baseball Baseball is a bat-and-ball games, bat-and-ball game played between two opposing teams who take turns batting (baseball), batting and fielding. The game proceeds when a player on the fielding team (baseball), fielding team, called the pi ...

baseball
and
boxing Boxing is a in which two people, usually wearing and other protective equipment such as hand wraps and mouthguards, throw at each other for a predetermined amount of time in a . is both an and sport and is a standard fixture in most inte ...

boxing
. Other, sports-specific factors may the advantage left-handers usually hold in one-on-one situations: * In
cricket Cricket is a bat-and-ball gameBat-and-ball may refer to: *Bat-and-ball games Bat-and-ball games (or safe haven games) are field games played by two opposing teams, in which the action starts when the defending team throws a ball at a ded ...

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
average In colloquial language, an average is a single number taken as representative of a non-empty list of numbers. Different concepts of average are used in different contexts. Often "average" refers to the arithmetic mean, the sum of the numbers divide ...
(''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 Wasim Akram (born 3 June 1966) is a Pakistani cricket commentator, coach, and former cricketer and captain Captain is a title for the commander of a military unit, the commander of a ship, aeroplane, spacecraft, or other vessel, or the co ...

Wasim Akram
). * In
baseball Baseball is a bat-and-ball games, bat-and-ball game played between two opposing teams who take turns batting (baseball), batting and fielding. The game proceeds when a player on the fielding team (baseball), fielding team, called the pi ...

baseball
, a right-handed pitcher's
curve ball Image:12-6 Curveball.gif, 200px, An animated diagram of a 12–6 curveball In baseball and softball, the curveball is a type of pitch (baseball), pitch thrown with a characteristic grip and hand movement that imparts forward spin to the baseball ...
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 Major League Baseball (MLB) is an American professional baseball Professional baseball is organized baseball in which players are selected for their talents and are paid to play for a specific team or club system. It is played in baseball lea ...

MLB
players is closer to 39% of hitters and 28% of pitchers, according to 2012 data. Historical batting averages show that left-handed batters have a slight advantage over right-handed batters when facing right-handed pitchers. 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. Fourteen of the top twenty career batting averages in
Major League Baseball Major League Baseball (MLB) is a professional baseball Professional baseball is organized baseball in which players are selected for their talents and are paid to play for a specific team or club system. It is played in baseball league, leag ...
history have been posted by left-handed batters. 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. ** 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
pick offIn baseball, a pickoff is an act by a pitcher or catcher, throwing a live ball (baseball), live ball to a Infielder, fielder so that the fielder can tag out a baserunner who is either lead off, leading off or about to begin stolen base, stealing the ...

pick off
baserunners at first base. ** Defensively in baseball, left-handedness is considered an advantage for
first basemen A first baseman, abbreviated 1B, is the player on a baseball or softball team who fields the area nearest first base, the first of four bases a baserunner must touch in succession to score a run. The first baseman is responsible for the majority ...
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 An infielder is a baseball player stationed at one of four defensive "infield" positions on the baseball field. Standard arrangement of positions In a game of baseball, two teams of nine players take turns playing offensive and defensive roles. ...
. 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. A left-handed catcher would have a potentially more dangerous time tagging out a baserunner trying to score. 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. On the other hand, the Encyclopedia of Baseball Catchers states: * 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 Handball (also known as team handball, European handball or Olympic handball) is a team sport in which two teams of seven players each (six outcourt players and a Handball goalkeeper, goalkeeper) pass a ball using their hands with the aim of th ...

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 Water polo is a competitive sport, competitive team sport played in water between two teams of seven players each. The game consists of four quarters in which the two teams attempt to score goals by throwing the water polo ball, ball into the ...
, 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 Ice hockey is a contact Contact may refer to: Interaction Physical interaction * Contact (geology)A geological contact is a boundary which separates one rock body from another. A contact can be formed during deposition, by the intrusio ...

Ice hockey
typically uses a strategy in which a 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. * In
American football American football, referred to simply as football in the United States and Canada and also known as gridiron, is a team sport played by two teams of eleven players on a rectangular American football field, field with goalposts at each end. ...

American football
, the handedness of a
quarterback The quarterback (commonly abbreviated "QB"), colloquially known as the "signal caller", is a position in gridiron football Gridiron football,
quarterback
affects blocking patterns on the
offensive line Image:Linemen.svg, 350px, A diagram of the linemen, with defensive linemen (in 4-3 formation) in red and offensive linemen in green. In gridiron football, a lineman is a player who specializes in play at the line of scrimmage. The linemen of the ...
.
Tight end The tight end (TE) is a position in American football, arena football, and Canadian football, on the offense (sports), offense. The tight end is often a hybrid position with the characteristics and roles of both an offensive lineman and a wide re ...
s, when only one is used, typically line up on the same side as the throwing hand of the quarterback, while the
offensive tackle Offensive may refer to: * Offensive, the former name of the Dutch political party Socialist Alternative * Offensive (military) An offensive is a that seeks through an aggressive projection of armed forces to occupy territory, gain an or achi ...
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. While uncommon, there have been several notable left-handed quarterbacks. * In
bowling Bowling is a Throwing sports#Target sports, target sport and recreational activity in which a player rolls a bowling ball, ball toward Bowling pin, pins (in pin bowling) or another target (in target bowling). The term ''bowling'' usually refe ...

bowling
, the oil pattern used on the bowling lane 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.


Sex

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 that men are 23% likelier to be left-handed. In terms of proportions this odds ratio implies that if the incidence of left-handedness for females was 10%, then the incidence of male left-handedness would be 12%.


Sexuality and gender identity

A number of studies examining the relationship between handedness and sexual orientation have reported that a disproportionate minority of homosexual people exhibit left-handedness, though findings are mixed. A 2001 study also found that boys whose
gender identity Gender identity is the personal sense of one's own gender Gender is the range of characteristics pertaining to, and differentiating between femininity Femininity (also called womanliness or girlishness) is a set of attributes, behavior ...
is not male were more than twice as likely to be left-handed than a clinical
control group In the design of experiments The design of experiments (DOE, DOX, or experimental design) is the design of any task that aims to describe and explain the variation of information under conditions that are hypothesized to reflect the variation. ...

control group
(19.5% vs. 8.3%, respectively).
Paraphilia Paraphilia (previously known as sexual perversion and sexual deviation) is the experience of intense sexual arousal Sexual arousal (also sexual excitement) is typically the arousal Arousal is the physiological and psychological ...
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". Greater rates of left-handedness has also been documented among
pedophiles Pedophilia ( alternatively spelt paedophilia) is a psychiatric disorder in which an adult or older adolescent experiences a primary or exclusive sexual attraction Sexual attraction is attraction on the basis of sexual desire or the qualit ...
. A 2014 study attempting to analyze the biological markers of
asexuality Asexuality is the lack of sexual attraction to others, or low or absent interest in or Sexual desire, desire for Human sexual activity, sexual activity. It may be considered a sexual orientation or the lack thereof. It may also be categorized ...

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.


Mortality rates in combat

A study at
Durham University , mottoeng = Her foundations are upon the holy hills ( Psalm 87:1) , established = (university status) , type = Public In public relations Public relations (PR) is the practice of managing and disseminating information from an in ...

Durham University
— which examined mortality data for
cricketers Cricket is a Bat-and-ball games, bat-and-ball game played between two teams of eleven players on a cricket field, field at the centre of which is a cricket pitch, pitch with a wicket at each end, each comprising two Bail (cricket), bails bal ...

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. 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. 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.


Episodic memory

A high level of handedness (whether strongly favoring right or left) is associated with poorer
episodic memory Episodic may refer to: * The nature of television series that are divided into short programs known as episodes * Episodic memory, types of memory that result from specific incidents in a lifetime * In Geology Geology (from the Ancient Greek ...
, and with poorer communication between brain hemispheres, which may give poorer emotional processing, although bilateral stimulation may reduce such effects.


Corpus callosum

A high level of handedness is associated with a smaller
corpus callosum The corpus callosum (Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Repu ...

corpus callosum
whereas low handedness with a larger one.


In culture

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." As a child British King
George VI George VI (Albert Frederick Arthur George; 14 December 1895 – 6 February 1952) was King of the United Kingdom There have been 12 monarchy of the United Kingdom, British monarchs since the political union of the Kingdom of England an ...

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. McManus noted that, as the
Industrial Revolution The Industrial Revolution was the transition to new manufacturing processes in Great Britain, continental Europe Continental Europe or mainland Europe is the contiguous continent A continent is any of several large landmasse ...
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 A dip pen or nib pen or pen nib usually consists of a metal nib with capillary channels like those of fountain pen File:Different fountain pens.jpg, Various contemporary and vintage fountain pens (left to right) Pilot Justus 95, Pelikan Souver ...

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.


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 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'' 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 , ''gauche'' means both "left" and "awkward" or "clumsy", while ''droit(e)'' (
cognate In linguistics Linguistics is the scientific study of language A language is a structured system of communication Communication (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Itali ...
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 Taiwan, officially the Republic of China (ROC), is a country in East Asia East Asia is the eastern region of Asia Asia () is Earth's largest and most populous continent, located primarily in the Eastern Hemisphere, Eastern and N ...

Taiwan
(and still in
Mainland China The term "mainland China" refers to the area directly governed by the People's Republic of China China (), officially the People's Republic of China (PRC; ), is a country in East Asia. It is the world's List of countries and dependencies ...

Mainland China
,
Japan Japan ( ja, 日本, or , and formally ) is an island country An island country or an island nation is a country A country is a distinct territory, territorial body or political entity. It is often referred to as the land of an in ...

Japan
and ), 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 Stroke order is the order in which the Stroke (CJK character), strokes of a Chinese character (or Chinese family of scripts#Adaptations for other languages, Chinese derivative character) are written. A stroke is a movement of a writing instru ...
, 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. 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 The Latin alphabet or Roman alphabet is the collection of letters originally used by the ancient Romans In historiography Historiography is the study of the methods of historian ( 484– 425 BC) was a Greek historian who lived ...

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. 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. In the Soviet Union, all left-handed children were forced to write with their right hand in the Soviet school system.А. П. Чуприков, Е. А. Волков. // Мир леворуких. Киев. 2008.


International Left-Handers Day

International Left-Handers Day is held annually every August 13. It was founded by the Left-Handers Club in 1992, with the club itself having been founded in 1990. 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." 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."


In other animals

Kangaroo The kangaroo is a marsupial from the family Macropodidae (macropods, meaning "large foot"). In common use the term is used to describe the largest species from this family, the red kangaroo, as well as the antilopine kangaroo, eastern grey k ...

Kangaroo
s and other macropod
marsupial Marsupials are any members of the mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ' ...
s show a left-hand preference for everyday tasks in the wild. 'True' handedness is unexpected in marsupials however, because unlike
placental mammals Placentalia is one of the three extant subdivisions of the class of animals Mammalia; the other two are Monotremata and Marsupial Marsupials are any members of the mammal Mammals (from Latin language, Latin , 'breast') are a group ...

placental mammals
, they lack a
corpus callosum The corpus callosum (Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Repu ...

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 Arboreal locomotion is the locomotion Locomotion means the act or ability of an entity or person to transport or move oneself from place to place. Locomotion or Loco-Motion may refer to: Motion * Motion (physics) *Specific types of motion ** A ...
species. 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.


See also


General

*
Cardinal direction The four cardinal directions, or cardinal points, are the directions north, east, south, and west, commonly denoted by their initials N, E, S, and W. East and west are perpendicular (at right angles) to north and south, with east being in the c ...
*
Clockwise Two-dimensional rotation A rotation is a circular movement of an object around a center (or point) of rotation. The plane (geometry), geometric plane along which the rotation occurs is called the ''rotation plane'', and the imaginary line ...

Clockwise
, which also discusses counterclockwise/anticlockwise, the two terms for the opposite sense of rotation *
Dexter and sinister ''Dexter'' and ''sinister'' are terms used in heraldry Heraldry () is a discipline relating to the design, display and study of armorial bearings (known as armory), as well as related disciplines, such as vexillology, together with the study of ...
*
Footedness Footedness is the natural preference of one's left or right foot The foot (plural: feet) is an anatomical Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology Biology is the natural science that studies life and living or ...
*
Laterality The term laterality refers to the preference most humans show for one side of their Human body, body over the other. Examples include Handedness, left-handedness/right-handedness and left/right-footedness; it may also refer to the primary use of ...
*
Left- and right-hand traffic Left-hand traffic (LHT) and right-hand traffic (RHT) are the practices, in bidirectional traffic, of keeping to the left side or to the right side of the road, respectively. They are fundamental to traffic flow, and are sometimes referred to ...
*
Ocular dominance Ocular dominance, sometimes called eye preference or eyedness, is the tendency to prefer visual The visual system comprises the sensory organ A sense is a biological system A biological system is a complex network which connects several ...
(eyedness) * Proper right and proper left *
Relative direction Body relative directions (also known as egocentric coordinates) are geometrical orientations relative to a body such as a human Humans (''Homo sapiens'') are the most abundant and widespread species In biology, a species is the ...


Handedness

*
Edinburgh Handedness Inventory The Edinburgh Handedness Inventory is a measurement scale used to assess the dominance of a person's right or left hand in everyday activities, sometimes referred to as laterality The term laterality refers to the preference most humans Hu ...
*
Geschwind–Galaburda hypothesis The Geschwind–Galaburda hypothesis was proposed by Norman Geschwind and Albert Galaburda to explain Biology of gender, sex differences in cognition, cognitive abilities by relating them to lateralization of brain function. The basic idea is that ...
* Neuroanatomy of handedness * Situs inversus * Twins and handedness


References


External links


Lefties Have The Advantage In Adversarial Situations
ScienceDaily, April 14, 2006.
Science Creative Quarterly's overview of some of the genetic underpinnings of left-handedness

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)
"Breast Cancer Risk Doubles for Southpaw Women"
MedPage Today, 26 September. * Hansard (1998)

, Debate contribution by the Rt Hon. Mr. Peter Luff (MP for Mid-Worcestershire), House of Commons, 22 July. *
Handedness and Earnings

Higher paychecks: a left-handed compliment?

Handedness & earnings, published in Journal of Human Resources 2007

Handedness Research Institute


{{Authority control Handedness, Chirality Discrimination Mental processes Asymmetry ca:Dretà