In human biology, handedness is the 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. Right-handedness is most common; about 90% of people are right-handed. 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. 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 sports that involve 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, tennis, fencing, cricket, boxing and MMA.
- 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 is the change of hand preference between different tasks. This is very uncommon in the population with about a 1% prevalence.
- Ambidexterity 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.
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.
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. In a 2013 study, 39% of infants (6 to 14 months) and 97% of toddlers (18 to 24 months) demonstrated a hand preference.
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.
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 of handedness is roughly 24%.
However, growing evidence from linkage and genome-wide association studies suggests that genetic variance in handedness cannot be explained by a single genetic locus. From these studies, McManus et al. now conclude that handedness is polygenic and estimate that at least 40 loci contribute to the trait.
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. Brandler and 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).
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.
Twin studies indicate that genetic factors explain 25% of the variance in handedness, and environmental factors the remaining 75%. While the molecular basis of handedness epigenetics is largely unclear, Ocklenburg et al. (2017) found that asymmetric methylation of CpG sites plays a key role for gene expression asymmetries related to handedness.
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".
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 abnormalities or delay, and asymmetry of the vestibular cortex is strongly correlated with the direction of handedness.
Another theory is that 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 ultrasound screening (sonography used to check the healthy development of the fetus and mother) and left-handedness.
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
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.
Writing in Scientific American, 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 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. 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).
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.
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. 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.
Left-handed people are much more likely to have several specific physical and mental disorders and health problems. For example:
A variety of neuropsychiatric and developmental disorders like autism spectrum disorders, depression, bipolar disorder, anxiety disorders, schizophrenia, and alcoholism has been associated with left- and mixed-handedness.
A 2012 study showed that nearly 40% of children with cerebral palsy were left-handed, 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. 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.
Left-handed women have a higher risk of breast cancer than right-handed women and the effect is greater in post-menopausal women.
One systematic review 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.
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.
However, more recently, in a 2014 study published by the National Bureau of Economic Research, 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
This section needs additional citations for verification. (January 2013)
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. The term southpaw is sometimes used to refer to a left-handed individual, especially in baseball and boxing.
Other, sports-specific factors may 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 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).
- 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. 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 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 off baserunners at first base.
- 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. 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:
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 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, the handedness of a quarterback affects blocking patterns on the offensive line. Tight ends, 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. While uncommon, there have been several notable left-handed quarterbacks.
- In 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.
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%.[clarification needed]
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 children who were assigned male at birth and whose gender identity is not male were more than twice as likely to be left-handed than a clinical control group (19.5% vs. 8.3%, respectively).
Paraphilias (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.
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.
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. 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 etc
A high level of handedness (whether strongly favoring right or left) is associated with poorer episodic memory, and with poorer communication between brain hemispheres, which may give poorer emotional processing, although bilateral stimulation may reduce such effects.
A high level of handedness is associated with a smaller corpus callosum whereas low handedness with a larger one.
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 (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 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.
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, 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.
Until very recently in Taiwan (and still in Mainland China, Japan and 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. 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. 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.
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
Kangaroos and other macropod marsupials show a left-hand preference for everyday tasks in the wild. 'True' handedness is unexpected in marsupials however, because unlike 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. 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.
- Cardinal direction
- Clockwise, which also discusses counterclockwise/anticlockwise, the two terms for the opposite sense of rotation
- Dexter and sinister
- Left- and right-hand traffic
- Ocular dominance (eyedness)
- Proper right and proper left
- Relative direction
- Edinburgh Handedness Inventory
- Geschwind–Galaburda hypothesis
- Neuroanatomy of handedness
- Situs inversus
- Twins and handedness
- Holder MK. "What does Handedness have to do with Brain Lateralization (and who cares?)". Archived from the original on 2013-03-26. Retrieved 11 August 2012.
- "dominant". Merriam-Webster Dictionary. Merriam-Webster. Archived from the original on 8 March 2017. Retrieved 8 March 2017.
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
- "non-". Merriam-Webster Dictionary. Merriam-Webster. Archived from the original on 8 March 2017. Retrieved 8 March 2017.
Definition of non- 1 : not : other than : reverse of : absence of • nontoxic • nonlinear. ("Nondominant" is one of 945 words listed under "non-")
- Scharoun SM, Bryden PJ (2014). "Hand preference, performance abilities, and hand selection in children". Frontiers in Psychology. 5 (82): 82. doi:10.3389/fpsyg.2014.00082. PMC 3927078. PMID 24600414.
- Papadatou-Pastou, Marietta; Ntolka, Eleni; Schmitz, Judith; Martin, Maryanne; Munafò, Marcus R.; Ocklenburg, Sebastian; Paracchini, Silvia (June 2020). "Human handedness: A meta-analysis". Psychological Bulletin. 146 (6): 481–524. doi:10.1037/bul0000229. PMID 32237881.
- Santrock JW (2008). "A Topical Approach to Life-Span Development". In Ryan M (ed.). Motor, Sensory, and Perceptual Development. Boston, MA: McGraw-Hill Higher Education. pp. 172–205.
- "Here's Why Left-Handed Athletes Dominate One-on-One Sports". Curiosity.com. Archived from the original on 14 November 2019.[unreliable source?]
- "Why are left-handed people better fighters?". ITV News. 2019-02-25. Retrieved 2021-03-01.
- Holder MK (1997). "Why are more people right-handed?". Scientific American. Archived from the original on 2013-07-08. Retrieved 2008-04-14.
- Hardyck C, Petrinovich LF (May 1977). "Left-handedness". Psychological Bulletin. 84 (3): 385–404. doi:10.1037/0033-2909.84.3.385. PMID 859955.
- Annett, Marian (2002). Handedness and Brain Asymmetry. Psychology Press. Unknown parameter
- Nicholls, Michael E.R.; Thomas, Nicole A.; Loetscher, Tobias; Grimshaw, Gina M. (November 2013). "The Flinders Handedness survey (FLANDERS): A brief measure of skilled hand preference". Cortex. 49 (10): 2914–2926. doi:10.1016/j.cortex.2013.02.002. PMID 23498655. S2CID 4986724.
- Hepper PG, Wells DL, Lynch C (2005). "Prenatal thumb sucking is related to postnatal handedness". Neuropsychologia. 43 (3): 313–5. doi:10.1016/j.neuropsychologia.2004.08.009. PMID 15707608. S2CID 805957.
- Nelson EL, Campbell JM, Michel GF (April 2013). "Unimanual to bimanual: tracking the development of handedness from 6 to 24 months". Infant Behavior & Development. 36 (2): 181–8. doi:10.1016/j.infbeh.2013.01.009. PMC 3615031. PMID 23454419.
- Banich M (1997). Neuropsychology: The Neural Bases of Mental Function. ISBN 9780395666999.
- Rasmussen, T; Milner, B (1977). "The role of early left-brain injury in determining lateralization of cerebral speech functions". Annals of the New York Academy of Sciences. 30 (299): 355–369. Bibcode:1977NYASA.299..355R. doi:10.1111/j.1749-6632.1977.tb41921.x. PMID 101116. S2CID 10981238.
- Carey, David; Johnstone, Leah (2014). "Quantifying cerebral asymmetries for language in dextrals and adextrals with random-effects meta analysis". Frontiers in Psychology. 5: 1128. doi:10.3389/fpsyg.2014.01128. PMC 4219560. PMID 25408673.
- Cai, Q; Van Der Haegen, L; Brysbaert, M (2013). "Complementary hemispheric specialization for language production and visuospatial attention". PNAS. 110 (4): 322–330. doi:10.1073/pnas.1212956110. PMC 3557046. PMID 23297206.
- Karlsson, EMK; Johnstone, LT; Carey, DPC (2019). "The depth and breadth of multiple perceptual asymmetries in right handers and non-right handers". Laterality. 24 (6): 707–739. doi:10.1080/1357650X.2019.1652308. PMID 31399020. S2CID 199519317.
- McManus C (2003). Right Hand, Left Hand. Phoenix Paperbacks. ISBN 978-0753813553.
- Medland SE, Duffy DL, Wright MJ, Geffen GM, Hay DA, Levy F, et al. (January 2009). "Genetic influences on handedness: data from 25,732 Australian and Dutch twin families". Neuropsychologia. 47 (2): 330–7. doi:10.1016/j.neuropsychologia.2008.09.005. PMC 2755095. PMID 18824185.
- Annett M (2009). "The genetic basis of lateralization". In Sommer IE, Kahn RS (eds.). Language lateralization and psychosis. pp. 73–86. doi:10.1017/CBO9780511576744.006. hdl:2381/4737. ISBN 9780511576744. S2CID 53411957.
- Francks C, DeLisi LE, Fisher SE, Laval SH, Rue JE, Stein JF, Monaco AP (February 2003). "Confirmatory evidence for linkage of relative hand skill to 2p12-q11". American Journal of Human Genetics. 72 (2): 499–502. doi:10.1086/367548. PMC 379245. PMID 12596796.
- Francks C, Maegawa S, Laurén J, Abrahams BS, Velayos-Baeza A, Medland SE, et al. (December 2007). "LRRTM1 on chromosome 2p12 is a maternally suppressed gene that is associated paternally with handedness and schizophrenia". Molecular Psychiatry. 12 (12): 1129–39, 1057. doi:10.1038/sj.mp.4002053. PMC 2990633. PMID 17667961.
- Van Agtmael T, Forrest SM, Williamson R (October 2002). "Parametric and non-parametric linkage analysis of several candidate regions for genes for human handedness". European Journal of Human Genetics. 10 (10): 623–30. doi:10.1038/sj.ejhg.5200851. PMID 12357333.
- Warren DM, Stern M, Duggirala R, Dyer TD, Almasy L (November 2006). "Heritability and linkage analysis of hand, foot, and eye preference in Mexican Americans". Laterality. 11 (6): 508–24. doi:10.1080/13576500600761056. PMID 16966240. S2CID 11711104.
- Laval SH, Dann JC, Butler RJ, Loftus J, Rue J, Leask SJ, et al. (September 1998). "Evidence for linkage to psychosis and cerebral asymmetry (relative hand skill) on the X chromosome". American Journal of Medical Genetics. 81 (5): 420–7. doi:10.1002/(SICI)1096-8628(19980907)81:5<420::AID-AJMG11>3.0.CO;2-E. PMID 9754628.
- Armour JA, Davison A, McManus IC (March 2014). "Genome-wide association study of handedness excludes simple genetic models". Heredity. 112 (3): 221–5. doi:10.1038/hdy.2013.93. PMC 3931166. PMID 24065183.
- Eriksson N, Macpherson JM, Tung JY, Hon LS, Naughton B, Saxonov S, et al. (June 2010). "Web-based, participant-driven studies yield novel genetic associations for common traits". PLOS Genetics. 6 (6): e1000993. doi:10.1371/journal.pgen.1000993. PMC 2891811. PMID 20585627.
- Scerri TS, Brandler WM, Paracchini S, Morris AP, Ring SM, Richardson AJ, et al. (February 2011). "PCSK6 is associated with handedness in individuals with dyslexia". Human Molecular Genetics. 20 (3): 608–14. doi:10.1093/hmg/ddq475. PMC 3016905. PMID 21051773.
- McManus IC, Davison A, Armour JA (June 2013). "Multilocus genetic models of handedness closely resemble single-locus models in explaining family data and are compatible with genome-wide association studies". Annals of the New York Academy of Sciences. 1288 (1): 48–58. Bibcode:2013NYASA1288...48M. doi:10.1111/nyas.12102. PMC 4298034. PMID 23631511.
- Brandler WM, Morris AP, Evans DM, Scerri TS, Kemp JP, Timpson NJ, et al. (September 2013). "Common variants in left/right asymmetry genes and pathways are associated with relative hand skill". PLOS Genetics. 9 (9): e1003751. doi:10.1371/journal.pgen.1003751. PMC 3772043. PMID 24068947.
- Brandler WM, Paracchini S (February 2014). "The genetic relationship between handedness and neurodevelopmental disorders". Trends in Molecular Medicine. 20 (2): 83–90. doi:10.1016/j.molmed.2013.10.008. PMC 3969300. PMID 24275328.
- Wiberg A, Ng M, Al Omran Y, Alfaro-Almagro F, McCarthy P, Marchini J, et al. (October 2019). "Handedness, language areas and neuropsychiatric diseases: insights from brain imaging and genetics". Brain. 142 (10): 2938–2947. doi:10.1093/brain/awz257. PMC 6763735. PMID 31504236.
- Medland, Sarah E.; Duffy, David L.; Wright, Margaret J.; Geffen, Gina M.; Martin, Nicholas G. (1 February 2006). "Handedness in Twins: Joint Analysis of Data From 35 Samples". Twin Research and Human Genetics. 9 (1): 46–53. doi:10.1375/183242706776402885. PMID 16611467. S2CID 38843437.
- Sun T, Collura RV, Ruvolo M, Walsh CA (July 2006). "Genomic and evolutionary analyses of asymmetrically expressed genes in human fetal left and right cerebral cortex". Cerebral Cortex. 16 Suppl 1 (Suppl 1): i18-25. doi:10.1093/cercor/bhk026. PMID 16766703.
- Ocklenburg S, Schmitz J, Moinfar Z, Moser D, Klose R, Lor S, et al. (February 2017). "Epigenetic regulation of lateralized fetal spinal gene expression underlies hemispheric asymmetries". eLife. 6. doi:10.7554/eLife.22784. PMC 5295814. PMID 28145864.
- Titus-Ernstoff, Linda; Perez, Kimberly; Hatch, Elizabeth E.; Troisi, Rebecca; Palmer, Julie R.; Hartge, Patricia; Hyer, Marianne; Kaufman, Raymond; Adam, Ervin; Strohsnitter, William; Noller, Kenneth; Pickett, Kate E.; Hoover, Robert (March 2003). "Psychosexual Characteristics of Men and Women Exposed Prenatally to Diethylstilbestrol". Epidemiology. 14 (2): 155–160. doi:10.1097/01.EDE.0000039059.38824.B2. PMID 12606880. S2CID 31181675.
- Scheirs JG, Vingerhoets AJ (October 1995). "Handedness and other laterality indices in women prenatally exposed to DES". Journal of Clinical and Experimental Neuropsychology. 17 (5): 725–30. doi:10.1080/01688639508405162. PMID 8557813.
- Schachter SC (May 1994). "Handedness in women with intrauterine exposure to diethylstilbestrol". Neuropsychologia. 32 (5): 619–23. doi:10.1016/0028-3932(94)90149-x. PMID 8084419. S2CID 44387790.
- Smith LL, Hines M (July 2000). "Language lateralization and handedness in women prenatally exposed to diethylstilbestrol (DES)". Psychoneuroendocrinology. 25 (5): 497–512. doi:10.1016/s0306-4530(00)00005-6. PMID 10818283. S2CID 44323126.
- Previc FH (January 1996). "Nonright‐handedness, central nervous system and related pathology, and its lateralization: A reformulation and synthesis". Developmental Neuropsychology. 12 (4): 443–515. doi:10.1080/87565649609540663.
- Dieterich M, Bense S, Lutz S, Drzezga A, Stephan T, Bartenstein P, Brandt T (September 2003). "Dominance for vestibular cortical function in the non-dominant hemisphere". Cerebral Cortex. 13 (9): 994–1007. doi:10.1093/cercor/13.9.994. PMID 12902399.
- Salvesen KÅ (September 2011). "Ultrasound in pregnancy and non-right handedness: meta-analysis of randomized trials". Ultrasound in Obstetrics & Gynecology. 38 (3): 267–71. doi:10.1002/uog.9055. PMID 21584892. S2CID 5135695.
- Fagard J, Lockman JJ (2005). "The effect of task constraints on infants' (bi)manual strategy for grasping and exploring objects". Infant Behavior and Development. 28 (3): 305–315. doi:10.1016/j.infbeh.2005.05.005.
- McManus C. "Right-Hand, Left-Hand official website". Archived from the original on 2012-05-04. Retrieved 1 June 2006.
- McManus C (14 April 2012). "Is It True That Left-Handed People Are Smarter Than Right-Handed People?". Scientific American Mind.
- Goodman, Joshua (1 November 2014). "The Wages of Sinistrality: Handedness, Brain Structure, and Human Capital Accumulation". Journal of Economic Perspectives. 28 (4): 193–212. doi:10.1257/jep.28.4.193.
- Ntolka E, Papadatou-Pastou M (January 2018). "Right-handers have negligibly higher IQ scores than left-handers: Systematic review and meta-analyses". Neuroscience and Biobehavioral Reviews. 84: 376–393. doi:10.1016/j.neubiorev.2017.08.007. PMID 28826694. S2CID 33792592.
- Nelson EL, Campbell JM, Michel GF (March 2014). "Early handedness in infancy predicts language ability in toddlers". Developmental Psychology. 50 (3): 809–14. doi:10.1037/a0033803. PMC 4059533. PMID 23855258.
- Deutsch, D (3 February 1978). "Pitch memory: an advantage for the left-handed". Science. 199 (4328): 559–560. Bibcode:1978Sci...199..559D. doi:10.1126/science.622558. PMID 622558. S2CID 2274951.
- Deutsch, Diana (1980). "Handedness and Memory for Tonal Pitch". Neuropsychology of Left-Handedness. pp. 263–271. doi:10.1016/B978-0-12-343150-9.50016-0. ISBN 978-0-12-343150-9.
- Deutsch D (2019). Musical Illusions and Phantom Words: How Music and Speech Unlock Mysteries of the Brain. Oxford University Press. ISBN 9780190206833. LCCN 2018051786.[page needed]
- Powell A (2015-01-30). "A lefty's lament". Harvard Gazette. Archived from the original on 2015-12-23. Retrieved 2015-12-29.
- Hirnstein M, Hugdahl K (October 2014). "Excess of non-right-handedness in schizophrenia: meta-analysis of gender effects and potential biases in handedness assessment". The British Journal of Psychiatry. 205 (4): 260–7. doi:10.1192/bjp.bp.113.137349. PMID 25274314.
- Lin KR, Prabhu V, Shah H, Kamath A, Joseph B (2015). "Handedness in diplegic cerebral palsy". Developmental Neurorehabilitation. 15 (5): 386–9. doi:10.3109/17518423.2012.696736. PMID 22758776. S2CID 6972136.
- Gardener H, Gao X, Chen H, Schwarzschild MA, Spiegelman D, Ascherio A (August 2010). "Prenatal and early life factors and risk of Parkinson's disease". Movement Disorders. 25 (11): 1560–7. doi:10.1002/mds.23339. PMC 3132935. PMID 20740569.
- Gardener H, Munger K, Chitnis T, Spiegelman D, Ascherio A (May 2009). "The relationship between handedness and risk of multiple sclerosis". Multiple Sclerosis. 15 (5): 587–92. doi:10.1177/1352458509102622. PMC 2771381. PMID 19389750.
- Fritschi L, Divitini M, Talbot-Smith A, Knuiman M (September 2007). "Left-handedness and risk of breast cancer". British Journal of Cancer. 97 (5): 686–7. doi:10.1038/sj.bjc.6603920. PMC 2360366. PMID 17687338.
- Hughes JR, Dorner E, Wind M (October 2008). "Is the decreased longevity among left-handers related to an increase in heart disease?". Clinical EEG and Neuroscience. 39 (4): 182–4. doi:10.1177/155005940803900406. PMID 19044215. S2CID 21369165.
- Luetters CM, Kelsey JL, Keegan TH, Quesenberry CP, Sidney S (November 2003). "Left-handedness as a risk factor for fractures". Osteoporosis International. 14 (11): 918–22. doi:10.1007/s00198-003-1450-z. PMID 14530828. S2CID 32654176.
- "Three Myths and Three Facts About Left-Handers". Psychology Today.
- Knight W (8 December 2004). "Left-handers win in hand-to-hand combat". New Scientist. Archived from the original on 27 October 2016. Retrieved 27 October 2016.
- Waldfogel J (15 August 2006). "Sinister and Rich: The evidence that lefties earn more". Slate. Archived from the original on 2010-01-12.
- Widermann D, Barton RA, Hill RA (2011). "Evolutionary perspectives on sport and competition". In Roberts SC (ed.). Applied Evolutionary Psychology. Oxford University Press. doi:10.1093/acprof:oso/9780199586073.001.0001. ISBN 9780199586073.
- "southpaw, n. and adj.". Oxford English Dictionary (3rd ed.). Oxford University Press. June 2011. Retrieved 5 July 2020.
- Peterson D (17 March 2017). "Righties vs Lefties - The Importance Of Handedness Training In Hitting". Game Sense Sports. Game Sense Sports. Archived from the original on 3 April 2019. Retrieved 3 April 2019.
- "2012 Major League Baseball Batting Splits". Baseball Reference. Archived from the original on 9 September 2015. Retrieved 6 March 2013.
- Walsh J. "The advantage of batting left-handed". hardballtimes.com. Archived from the original on 13 March 2013. Retrieved 7 March 2013.
- "Career Leaders & Records for Batting Average". Baseball Reference. Archived from the original on 13 April 2013. Retrieved 6 March 2013.
- "First Base Pickoffs for Lefty Pitchers". isport.com. Archived from the original on 22 June 2013. Retrieved 7 March 2013.
- Miller S (29 March 2009). "The Decline of Left-Handed First Basemen". nytimes.com. Archived from the original on 26 September 2015. Retrieved 7 March 2013.
- "Left Handed Catchers". The Encyclopedia of Baseball Catchers. Archived from the original on 17 August 2012. Retrieved 7 March 2013.
- Hoppe B (January 23, 2017). "Depleted Sabres defense thrives". Buffalo Hockey Beat. Olean Times Herald. Archived from the original on December 16, 2018. Retrieved January 23, 2017.
- Greene, Nick (2 November 2020). "Why Left-Handed Quarterbacks Are So Rare". Slate. Retrieved 5 November 2020.
- Papadatou-Pastou M, Martin M, Munafò MR, Jones GV (September 2008). "Sex differences in left-handedness: a meta-analysis of 144 studies". Psychological Bulletin. 134 (5): 677–699. doi:10.1037/a0012814. PMID 18729568.
- Lalumière ML, Blanchard R, Zucker KJ (July 2000). "Sexual orientation and handedness in men and women: a meta-analysis". Psychological Bulletin. 126 (4): 575–92. doi:10.1037/0033-2909.126.4.575. PMID 10900997.
- Mustanski BS, Bailey JM, Kaspar S (February 2002). "Dermatoglyphics, handedness, sex, and sexual orientation". Archives of Sexual Behavior. 31 (1): 113–22. doi:10.1023/A:1014039403752. PMID 11910784. S2CID 29217315.
- Williams, Terrance J.; Pepitone, Michelle E.; Christensen, Scott E.; Cooke, Bradley M.; Huberman, Andrew D.; Breedlove, Nicholas J.; Breedlove, Tessa J.; Jordan, Cynthia L.; Breedlove, S. Marc (March 2000). "Finger-length ratios and sexual orientation". Nature. 404 (6777): 455–456. Bibcode:2000Natur.404..455W. doi:10.1038/35006555. PMID 10761903. S2CID 205005405.
- Schwartz G, Kim RM, Kolundzija AB, Rieger G, Sanders AR (February 2010). "Biodemographic and physical correlates of sexual orientation in men". Archives of Sexual Behavior. 39 (1): 93–109. doi:10.1007/s10508-009-9499-1. PMID 19387815. S2CID 24358057.
- Zucker KJ, Beaulieu N, Bradley SJ, Grimshaw GM, Wilcox A (September 2001). "Handedness in boys with gender identity disorder". Journal of Child Psychology and Psychiatry, and Allied Disciplines. 42 (6): 767–76. doi:10.1111/1469-7610.00773. PMID 11583249. S2CID 4987839.
- Rahman Q, Symeonides DJ (February 2008). "Neurodevelopmental correlates of paraphilic sexual interests in men". Archives of Sexual Behavior. 37 (1): 166–72. doi:10.1007/s10508-007-9255-3. PMID 18074220. S2CID 22274418.
- Blanchard R, Kolla NJ, Cantor JM, Klassen PE, Dickey R, Kuban ME, Blak T (September 2007). "IQ, handedness, and pedophilia in adult male patients stratified by referral source". Sexual Abuse. 19 (3): 285–309. doi:10.1177/107906320701900307. PMID 17634757. S2CID 220359453.
- Cantor JM, Klassen PE, Dickey R, Christensen BK, Kuban ME, Blak T, et al. (August 2005). "Handedness in pedophilia and hebephilia". Archives of Sexual Behavior. 34 (4): 447–59. doi:10.1007/s10508-005-4344-7. PMID 16010467. S2CID 6427342.
- Bogaert AF (2001). "Handedness, criminality, and sexual offending". Neuropsychologia. 39 (5): 465–9. doi:10.1016/S0028-3932(00)00134-2. PMID 11254928. S2CID 28513717.
- Dyshniku F, Murray ME, Fazio RL, Lykins AD, Cantor JM (November 2015). "Minor Physical Anomalies as a Window into the Prenatal Origins of Pedophilia". Archives of Sexual Behavior. 44 (8): 2151–9. doi:10.1007/s10508-015-0564-7. PMID 26058490. S2CID 25667170.
- Yule MA, Brotto LA, Gorzalka BB (February 2014). "Biological markers of asexuality: Handedness, birth order, and finger length ratios in self-identified asexual men and women". Archives of Sexual Behavior. 43 (2): 299–310. doi:10.1007/s10508-013-0175-0. PMID 24045903. S2CID 5347734.
- Aggleton JP, Kentridge RW, Neave NJ (June 1993). "Evidence for longevity differences between left handed and right handed men: an archival study of cricketers". Journal of Epidemiology and Community Health. 47 (3): 206–9. doi:10.1136/jech.47.3.206. PMC 1059767. PMID 8350033.
- Jonathan R (February 1995). "Left For Dead". Wisden Cricket Monthly.
- Brown W. "Science: Sudden death for left-handers". New Scientist. Retrieved 2020-02-01.
- Propper RE, Christman SD, Phaneuf KA (June 2005). "A mixed-handed advantage in episodic memory: a possible role of interhemispheric interaction". Memory & Cognition. 33 (4): 751–7. doi:10.3758/BF03195341. PMID 16248339. S2CID 2989930.
- Sahu A, Christman SD, Propper RE (November 2016). "The contributions of handedness and working memory to episodic memory". Memory & Cognition. 44 (8): 1149–1156. doi:10.3758/s13421-016-0625-8. PMID 27259533.
- Prichard E, Propper RE, Christman SD (2013). "Degree of Handedness, but not Direction, is a Systematic Predictor of Cognitive Performance". Frontiers in Psychology. 4: 9. doi:10.3389/fpsyg.2013.00009. PMC 3560368. PMID 23386836.
- Shobe ER (2014-04-22). "Independent and collaborative contributions of the cerebral hemispheres to emotional processing". Frontiers in Human Neuroscience. 8: 230. doi:10.3389/fnhum.2014.00230. PMC 4001044. PMID 24795597.
- Spielberg JM, Heller W, Miller GA (2013-06-17). "Hierarchical brain networks active in approach and avoidance goal pursuit". Frontiers in Human Neuroscience. 7: 284. doi:10.3389/fnhum.2013.00284. PMC 3684100. PMID 23785328.
- Luders, Eileen; Cherbuin, Nicolas; Thompson, Paul M.; Gutman, Boris; Anstey, Kaarin J.; Sachdev, Perminder; Toga, Arthur W. (August 2010). "When more is less: Associations between corpus callosum size and handedness lateralization". NeuroImage. 52 (1): 43–49. doi:10.1016/j.neuroimage.2010.04.016. PMC 2903194. PMID 20394828.
- Kushner, Howard I (June 2011). "Retraining the King's left hand". The Lancet. 377 (9782): 1998–1999. doi:10.1016/s0140-6736(11)60854-4. PMID 21671515. S2CID 35750495.
- McManus, I. C. (2009). "The history and geography of human handedness". In Sommer, Iris E. C; Kahn, Rene S (eds.). Language Lateralization and Psychosis. pp. 37–58. doi:10.1017/CBO9780511576744.004. ISBN 978-0-511-57674-4.
- "A question of the left being right – and normal". China Daily. February 22, 2008. Archived from the original on January 24, 2011. Retrieved 2011-01-19.
- "Erste deutsche Beratungs- und Informationsstelle für Linkshänder und umge-schulte Linkshänder". lefthander-consulting.org (in German). Archived from the original on 2013-09-22. Retrieved 21 September 2013.
- "Teaching Left-Handers to Write". Handedness Research Institute. Archived from the original on 2013-09-23. Retrieved 21 September 2013.
- 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.
- А. П. Чуприков, Е. А. Волков. // Мир леворуких. Киев. 2008.
- "Left-Handers' Day August 13th: Celebrate your right to be left-handed". lefthandersday.com. Archived from the original on 2014-07-15. Retrieved 12 August 2013.
- "All kangaroos are lefties, scientists say". Sci-News.com. June 18, 2015. Archived from the original on June 19, 2015. Retrieved June 19, 2015.
- Callaway E (24 July 2009). "Is your cat left or right pawed?". New Scientist. Archived from the original on 7 November 2016. Retrieved 6 November 2016.