right-hander

　 　

WordNet

1. a person who uses the right hand more skillfully than the left (同)right_hander, righthander
2. toward or on the right; also used figuratively; "he looked right and left"; "the party has moved right"
3. (frequently plural) the interest possessed by law or custom in some intangible thing; "mineral rights"; "film rights"
4. anything in accord with principles of justice; "he feels he is in the right"; "the rightfulness of his claim" (同)rightfulness
5. a turn toward the side of the body that is on the south when the person is facing east; "take a right at the corner"
6. the hand that is on the right side of the body; "he writes with his right hand but pitches with his left"; "hit him with quick rights to the body" (同)right_hand
7. those who support political or social or economic conservatism; those who believe that things are better left unchanged (同)right wing
8. an abstract idea of that which is due to a person or governmental body by law or tradition or nature; "they are endowed by their Creator with certain unalienable Rights"; "Certain rights can never be granted to the government but must be kept in the hands
9. location near or direction toward the right side; i.e. the side to the south when a person or object faces east; "he stood on the right"
10. make reparations or amends for; "right a wrongs done to the victims of the Holocaust" (同)compensate, redress, correct
11. correct in opinion or judgment; "time proved him right" (同)correct
12. exactly; "he fell flop on his face" (同)flop
13. an interjection expressing agreement (同)right on
14. intended for the right hand; "a right-hand glove" (同)right-hand
15. (of the side of cloth or clothing) facing or intended to face outward; "the right side of the cloth showed the pattern"; "be sure your shirt is right side out"
16. being or located on or directed toward the side of the body to the east when facing north; "my right hand"; "right center field"; "a right-hand turn"; "the right bank of a river is the bank on your right side when you are facing downstream"
17. completely; "she felt right at home"; "he fell right into the trap"
18. having the axis perpendicular to the base; "a right angle"
19. immediately; "she called right after dinner"
20. in conformance with justice or law or morality; "do the right thing and confess"
21. in or into a satisfactory condition; "things are right again now"; "put things right"
22. of or belonging to the political or intellectual right
23. precisely, exactly; "stand right here!"
24. put in or restore to an upright position; "They righted the sailboat that had capsized"
25. regain an upright or proper position; "The capsized boat righted again"
26. guide or conduct or usher somewhere; "hand the elderly lady into the taxi"
27. a unit of length equal to 4 inches; used in measuring horses; "the horse stood 20 hands"
28. physical assistance; "give me a hand with the chores" (同)helping hand
29. a rotating pointer on the face of a timepiece; "the big hand counts the minutes"
30. terminal part of the forelimb in certain vertebrates (e.g. apes or kangaroos); "the kangaroos forearms seem undeveloped but the powerful five-fingered hands are skilled at feinting and clouting"- Springfield (Mass.) Union
31. the cards held in a card game by a given player at any given time; "I didnt hold a good hand all evening"; "he kept trying to see my hand" (同)deal
32. the (prehensile) extremity of the superior limb; "he had the hands of a surgeon"; "he extended his mitt" (同)manus, mitt, paw
33. a member of the crew of a ship; "all hands on deck"
34. a position given by its location to the side of an object; "objections were voiced on every hand"
35. a round of applause to signify approval; "give the little lady a great big hand"
36. ability; "he wanted to try his hand at singing"
37. one of two sides of an issue; "on the one hand..., but on the other hand..."
38. connect or secure to; "They rigged the bomb to the ignition"
39. formation of masts, spars, sails, etc., on a vessel (同)rigging
40. gear (including necessary machinery) for a particular enterprise
41. manipulate in a fraudulent manner; "rig prices" (同)manipulate
42. arrange the outcome of by means of deceit; "rig an election" (同)set_up
43. equip with sails or masts; "rig a ship" (同)set, set_up

PrepTutorEJDIC

1. 右きき[の人] / 右打者,右腕投手
2. 《名試の前にのみ用いて》『右の』,右側の / 《しばしば『R-』》(政治上)『右派の』,保守的な / 〈U〉《the~》『右』,右側,右方 / 〈C〉『右手』(right hand) / 〈U〉《集合的に》《しばしばthe R-》(政治上の)右派,保守派 / 〈C〉(野球の)右翼(right field) / 『右に』,右側に,右方に
3. 《補語にのみ用いて》(道徳的に)『正しい』,正当な,正義の(just) / (人,人の判断・意見などが)『間偉いのない』,正しい(correct) / (事実に合って)『正しい』,正確な / 適切な,ぴったりの / (精神が)健全な,まともな;(心身が)健康な / 表の,正面の / 〈U〉(道徳的な)『正しさ』,正義;正しい行い / 〈C〉〈U〉(法律上・道徳上の)権利 / 〈U〉〈C〉《複数形で》(政治的・社会的な)人権,権利 / 《話》『まっすぐに』;まともに(directly) / 《話》『きっかり』,ちょうど(exactly) / 正確に,間違いなく(correctly) / (道徳的に)正しく,公正に / すっかり,完全に(completely);ずっと(all the way) / 適切に,ふさわしく;都合よく,うまく / 《おもに米話》すぐに,ただちに / 《特定の称号に付けて》非常に(very) / …‘を'正しい位置(状態)に戻す,立ち直らせる,整とんする / 〈誤りなど〉‘を'正す
4. 『手』(手首から先の部分) / (時計・計器の)針 / 《単数形で》筆跡 / 側,方(side): / 《a~》(…への)援助,手助け《+with(at, to)+名》 / 職工,職人,人手 / 乗組員 / 《前に形容詞を置いて》(…するのが)(じょうずな・へたな)人(+『at』+『名』(『doing』)》 / 《単数形》技量,腕前;(…の)やり方,扱い方《+『at』(『with』)+名》 / 《単数形で》拍手かっさい / 《文》《one's~,the,》結婚の承諾;確約 / (カードの)持ち札;一勝負 / 《しばしば複数形で》所有,管理 / ハンド(馬の高さを測る単位;4インチ) / 《『hand』+『名』〈間〉+『名』〈直〉=『hand』+『名』+『to』+『名』》…‘に'…‘を'『手渡す』,取ってやる / 《副詞[句]を伴って》〈人〉‘に'手を貸す / 手の(に関する),手のための / 手で操作する / 手持ちの
5. 〈船〉‘を'艤装(ぎそう)する / (マストなどを)〈船〉‘に'つける《+『名』+『with』+『名』》;(マストに)〈帆〉‘を'つける《+『名』+『to』+『名』》 / …‘に'装備をつける;…‘を'装備する《+『up』+『名,』+『名』+『up』》 / 船の装備(帆装),艤装(ぎそう) / (特定の目的のための)道具,用具 / 《英話》衣服,服装(clothing)
6. 〈他〉〈相場など〉を不正な手段であやつる

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/01/09 21:05:45」(JST)

wiki en

[Wiki en表示]

This article is about left and right handedness in humans. For other uses, see Handedness (disambiguation).

"Handed" redirects here. For other uses, see Handed (disambiguation).

"Southpaw" redirects here. For boxing stance, see Southpaw stance. For other uses, see Southpaw (disambiguation).

Handedness is a human attribute defined by unequal distribution of fine motor skills between the left and right hands. An individual who is more able with the right hand is called right-handed and one who is more skilled with the left is said to be left-handed. The majority of infants have developed hand preference by 6 months of age. A minority of adult people are equally skilled with both hands, and are termed ambidextrous. It is one example of body laterality.

The reasons for handedness, and why right-handedness is dominant are not known for certain, but a number of theories have been proposed.

Different types

A person writing the German word "Linkshänder" (left-hander) with the left hand

There are four main types of handedness:

• Right-handedness is most common. Right-handed people are more dexterous with their right hands when performing tasks. A variety of studies suggest that 70–90% of the world population is right-handed, rather than left-handed or any other form of handedness.
• Left-handedness is less common than right-handedness. Left-handed people are more dexterous with their left hands when performing tasks. A variety of studies suggest that approximately 10% of the world population is left-handed.
• Mixed-handedness, also known as cross-dominance, is being able to do different tasks better with different hands. For example, a mixed-handed person might write better with their left hand, but throw a ball more efficiently with their right. However, many writers define handedness by the hand used for writing, so mixed-handedness is often not included. Also, some tools may force mixed-handedness (e.g., scissors will not cut properly if held in the wrong hand, although scissors are manufactured in both lateral varieties). Most left-handed people develop some mixed-handedness simply by living in a world where most everyday objects are suited for right-handed people, or by growing up with right-handed parents.
• Ambidexterity is exceptionally rare, although it can be learned. A truly ambidextrous person is able to do any task equally well with either hand. Those who learn it still tend to sway towards their originally dominant hand.
• People who demonstrate awkwardness with both hands are said to be ambilevous or ambisinister. Ambisinistrous motor skills or a low level of dexterity may be the result of a debilitating physical condition.

Newer theories look at handedness in different ways from previously. The newer view is that handedness is not a simple preference for one hand because the two hands actually work together in more subtle ways. For example, when writing, it is not a simple matter of one hand being dominant and writing on the paper. For a right-handed person, the left hand is involved in important ways: it orients and grips the paper and provides the context from which the right hand operates. Thus the right hand appears specialized for finer movements and the left for broader, contextual movements.

Theories of handedness vs. non-handedness

See also: Lateralization of brain function and Laterality

Brain hemisphere division of labor

Division of labor is the most commonly accepted theory of handedness.^{[citation needed]} The premise of this theory is that since both motor control of speaking and handiwork require fine motor skills, having one hemisphere of the brain do both would be more efficient than having it divided up. Also, if all functions were carried out in both hemispheres, the size of the brain and its energy consumption would increase, which is not affordable. Since in most people, the left side of the brain controls speaking, right-handedness would prevail since the brain hemispheres control the opposite sides of the body.^{[citation needed]}

It has been suggested that handedness may initially have developed as a specialization causing improved throwing ability with language lateralization being a later development. Another suggestion is that infant handling on a particular side of the body allowed the other side to specialize on other tasks.

A possible objection is that the theory may predict that left-handed people would have a reversed brain division of labor.^{[citation needed]} In around 95% of right-handed people, and in over 50% of left-handed people, speech processing primarily takes place on the left side of the brain. Approximately 25% of left-handed people use both sides of the brain equally.

Another possible objection is that this does not explain why a particular brain hemisphere would predominantly be associated with certain tasks, such as the left hemisphere being associated with language in most people rather than the right or even both hemispheres being equally likely of being the dominant one regarding language. This is part of a more general problem regarding why functions and organs demonstrate predominant body laterality, such as situs solitus being the normal position of thoracic and abdominal organs.

Theories of left-handedness vs. right-handedness

The prevalence of right-handedness is universal across human cultures, although the percentage of right-handedness is smaller in primitive cultures.

Chimpanzees have a similar pattern with right-handedness being more common.

Some studies show preferences for one hand or one body side occurring as early as in the womb and in newborns and infants. These preferences are associated with later handedness. Hand orientation is developed in fetuses, most commonly determined by observing which hand is predominantly held close to the mouth.

Possible advantages of left-handedness

Some studies have shown that "...left-handers also tend to have unusually good visual-spatial skills and the ability to imagine spatial layouts." Santrock goes on to point out that mathematicians, musicians, architects, and artists are more commonly left-handers than would be expected. "Also, in one study of more than 100,000 students taking the Scholastic Aptitude Test (SAT), 20% of the top-scoring group was left-handed, twice the rate of left-handedness found in the general population (10%). Left-handedness may also reduce the risk of developing arthritis. However, Hardyck and Petrinovich reviewed a large literature and found no overall differences in mental ability in right-handers and non-right-handers.

Other reported associations include with higher creativity, a larger corpus callosum, certain right brain regions being larger, shorter transfer time of information between hemispheres, and higher socioeconomic status.

Possible disadvantages of left-handedness

Although there is little association with children's school performance in regards to handedness, some studies have shown problems in language development in left-handers. Research has shown left-handers are more likely to have problems with reading and they also "...don't do as well on phonology (the sound system of language) tasks..." when compared with right-handers. Also, in left-to-right languages, if left-handed writers move their left hands across what they have just written, they may smudge their writing. This situation is reversed in right-to-left languages such as Hebrew and Arabic.

Other reported associations that may have decreased evolutionary fitness include shorter adult height, lower weight, puberty at a later age, possibly a shorter life expectancy, increased risk of accidents, increased risk of certain neurological and immunological disorders, and decreased number of children.

Left-handedness and close combat

An evolutionary psychology explanation for the majority right-handedness / minority left-handedness pattern starts by suggesting that, in the ancestral environment, there would have been more disadvantages than advantages from left-handedness regarding overall inclusive fitness. This would explain why right-handedness is more common. That a significant minority still is left-handed may be due to negative frequency-dependent selection in which an advantageous trait becomes less advantageous the more common the trait is. It has been suggested that this may be due to left-handed people having an advantage in close combat as long as they rarely fight other left-handed people. This is because of right-handed people being unfamiliar with fighting the rare left-handed opponents, while left-handed people are relatively more familiar with fighting the more common right-handed opponents.

A 2004 study by Charlotte Faurie and Michel Raymond of the University of Montpellier II in France, published in the Proceedings of the Royal Society, argues that there is such a link. To support this, Faurie and Raymond surveyed nine undeveloped societies on five separate continents. Through a mix of direct observation and existing ethnographic data, they estimated the number of left-handed people within each population. They also looked at murder rates, thinking that those communities with higher murder rates might favor populations with more left-handed people, if left-handedness is a trait associated with greater fitness with regard to combat. Among these samples, they found strong support for the idea that, at least in primitive societies with higher levels of violence, left-handed people are more numerous. The researchers complemented with a discussion of the success of left-handers in certain sports.

This theory may also explain why left-handedness is more common in men than in women.

Spiral staircases and towers in castles typically spiral clockwise going up. This was meant to ensure that the (predominantly right-handed) defenders up the stairs had a good angle to swing swords and other weapons down at attackers. Conversely, right-handed attackers would find the weapons constantly colliding with the central pillar of the stairs. Hence, left-handed attackers gained an advantage.

The Bible (Judges 3:12–4:1) includes the story of Ehud, an Israelite judge who exploits his left-handedness to successfully assassinate an oppressive king. Since most swordsmen were right-handed, their swords would be worn on their left thigh, but Ehud concealed his weapon under his right, where it was not expected. This allowed him to sneak his sword into the palace without anyone's suspicion.

Left-handedness and sports

See also: Southpaw stance

Interactive sports such as table tennis, badminton, cricket, and tennis 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 advantage to players in one-on-one sports, such as tennis, boxing, fencing or judo, is that, in a population containing perhaps 10% left-handers and 90% right-handers, the left-hander plays 90% of his or her games against right-handed opponents and is well-practised at dealing with this asymmetry. Right-handers play 90% of their games against other right-handers. Thus, when confronted with left-handers, they are less practised (see Rafael Nadal). When two left-handers compete against each other, they are both likely to be at the same level of practice as when right-handers play other right-handers. This explains why a disproportionately high number of left-handers are found in sports in which direct one-on-one action predominates.

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 batter 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, left-handedness gives a pitcher an advantage over batters smaller than the advantage one would expect if one's calculations used experience as the only variable, but it confers yet other advantages that, depending on other aspects of a game scenario, may or may not bring the overall advantage back in line with expectations:
  • All else being equal (i.e., in a hypothetical situation where batters' experience against left-handed pitchers is equal to their experience against right-handed pitchers), a left-handed pitcher would challenge the average (i.e., right-handed) batter less than a right-handed pitcher would, because an opposite-handed pitcher's curve ball is easier to hit than a same-handed pitcher's - Because: a) a curve ball breaks toward the side of a pitcher opposite his pitching hand; and b) a curve ball breaking toward a batter is easier to hit than one breaking away from him, right-handed batters find left-handed pitchers' curve balls less difficult than right-handed pitchers' to hit.)
  • However, because a left-handed pitcher faces first base when throwing from the stretch position, whereas a right-hander throwing from "the stretch" has his back to first and instead faces third base, left-handed pitchers are generally better than right-handers at noticing and picking off baserunners attempting to steal second base. This advantage substantially outweighs the corresponding advantage that right-handers enjoy at picking off runners attempting to steal home plate: Although a runner's successfully stealing home does far more damage than does his stealing second, the expected benefit of an attempt to steal home (averaged across all situations featuring runners on third base) remains less than that of stealing second (averaged across all situations with a runner on first) because the catcher needs not throw to second base, the baserunner must avoid the batter's swing, and the swinging batter must avoid the runner. Moreover, the resulting rarity of attempts to steal home further diminish the advantage a right-hander enjoys.

Whether the sum of a left-hander's advantages exceed the sum of a right-hander's advantages depends on the game scenario, which includes not only the handedness of the pitcher, that of the batter, and the baserunner situation but also innumerable other factors including the game score, the specific hitting abilities of the batter in question, and the handedness, specific abilities, and lineup order of the opposing team's other players.

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.

Left-handed throwers are generally at a disadvantage to right-handers when playing the infield positions; the exception being first base. A left-handed thrower playing second base, third base or shortstop would need to pivot before making a throw to first base, thereby losing time and possibly accuracy on the throw. Conversely, a left-handed first baseman would not need to pivot when throwing to second or third base, as a right-handed first baseman would.

Few left-handed throwers have successfully played the catcher position (although in his youth, Babe Ruth, who threw left-handed, once played catcher for the St. Mary's Industrial Home's baseball team). Many attribute this to a perceived tendency for a left-hander's throw to "tail" in a manner not commonly associated with right-handed throwers, which presumably puts a left-handed catcher at a disadvantage when attempting to throw out would-be base stealers.

In sports in which one competitor's performance does not affect another's (except indirectly through subjectively perceived psychological pressure), a particular hand preference confers little or no advantage. Golf and miniature golf feature occasional situations when obstacles on one side of the ball but not the other interfere with the stance and/or swing of a right- or left-handed player but not the other's. Even so, the "favoritism" on any given course is probably minimal, especially at high levels of play: a layperson such as the owner of a small miniature golf business may, when placing obstacles, assess the results from only his/her own-"handed" perspective, such that more courses would be made difficult for right-handers than for left-handers. However, a thoughtful designer—especially a professional in the field—is likely to ensure game balance by adding handedness-specific obstacles in equal numbers and in places of similar tactical importance.

Hormones

Prenatal hormone imbalances may play a role in the gene expression for left-handedness. While the Geschwind–Galaburda testosterone hypothesis is often cited as cause, there is not any evidence to support the theory. However, more recent research has emerged suggesting that high prenatal estrogen exposure is a plausible alternative to Geschwind. In a study endorsed by the Centers for Disease Control (CDC), it is suggested that men who were prenatally exposed to diethylstilbestrol (a synthetic estrogen based fertility drug), are more likely to be left handed. Increased prenatal estrogen exposure in men, and its left-handed effect, may induce lower visual-spatial skills.

Environmental influences before and at birth

Birth stress

The "pathological left-hander" theory's basic premise is that left-handedness is due to brain damage during the birth process., yet there is no hard evidence and genetic causes are thought to be more important. Difficult or stressful births happen far more commonly among babies who grow up to be left-handed or ambidextrous.^{[citation needed]}

Prenatal vestibular asymmetry

Previc reviewed a large literature that points to the role of prenatal positioning during the final trimester and subsequent birth position as affecting handedness outcome, with about two-thirds of fetuses presenting with their left occiput 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 important for the development of handedness. In fact, every major disorder with 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.

Ultrasound

A popular theory is that ultrasound may affect the brains of unborn children, causing higher rates of left-handedness in children whose mothers received ultrasounds during pregnancy. Research on this topic suggests there may exist a weak association between ultrasound screening (sonography used to check on the healthy development of the fetus and mother during pregnancy) and non-right-handedness.

Twins theory

Twins theory: this theory postulates that left-handed individuals were originally part of an identical twin pair, with the right-handed twin fetus failing to develop early in development. Although Australian researchers claimed to have debunked the related vanishing twin theory, it is re-examined in Rik Smits's book "The Puzzle of Left-Handedness (2012)", which considers the fact that twin children have a high frequency of left-handedness / right-handedness in the pair.

Genetic factors

Handedness displays a complex inheritance pattern. For example, if both parents of a child are left-handed, there is only a 26% chance of that child also being left-handed. A large study of twins from 25,732 families by Medland et al. (2006) has indicated that the heritability of handedness is 24%. This suggests that the variation in handedness is in part determined by genetic variants, but there is a strong environmental component.

To date, two theoretical single gene models have been proposed to explain the patterns of inheritance of handedness, the first by Dr. Marian Annett of the University of Leicester and the second by Professor Chris McManus of UCL.

Both models propose that there is a variant in a single gene that has two alleles. Carriers of one allele are more likely to be right-handed, and the other allele does not specify the direction of handedness, instead leaving it to chance. They differ on the precise effect of the 'right-shift' allele, but both models provide similar fits to data on the inheritance of handedness. Oxford University psychiatrist Professor Tim Crow has taken the single-gene model one step further, and proposed that mutations in the gene PCDH11X were responsible for the evolution of handedness, cerebral asymmetry, language, susceptibility to schizophrenia, and was the speciation event that created Homo sapiens.

However, although single-gene models can be fitted to the data, they are too simplistic to explain the observed patterns of inheritance for handedness. PCDH11X may be of interest because it has both been duplicated onto the Y chromosome and shows evidence of accelerated evolution specifically in humans, but it is unclear if these changes are adaptive or if they are indeed relevant for cerebral asymmetry, handedness, or language acquisition. Furthermore, if alleles from a single gene alone were responsible for the variation in handedness, genetic linkage studies should have the power to identify that gene. However, a number of linkage studies have been performed, all of which have provided evidence for different regions of the genome contributing to variation in handedness including: 2p12-q11, 10q26, 12q21-23, and Xq21.

Out of these linkage studies, only one has led to the identification of a specific gene that is proposed to contribute to variation in handedness. Francks et al. (2007) discovered that alleles upstream of the gene LRRTM1 on chromosome 2 (2p12-q11) were linked to increased susceptibility to both left-handedness and schizophrenia. The gene is expressed only if inherited from the paternal side, and is turned off if inherited from the maternal side (genomic imprinting). However, linkage studies of complex traits are highly susceptible to false positives, and these results should be treated with caution until replicated using more powerful and larger scale genome-wide association studies. It remains to be seen precisely what role LRRTM1 plays in both schizophrenia and handedness.

Instead of performing a genome-wide study, Medland et al. took a candidate gene approach and found that CAG repeat length in the Androgen Receptor gene, AR, is positively correlated with left-handedness in females, and negatively correlated in males. This may help to explain why the prevalence of left-handedness is consistently observed to be higher in men compared to women (around 12% in men versus 10% in women globally).

Scerri, Brandler, and Paracchini et al. (2010), have performed the only published genome-wide association study for handedness that has identified a gene that is significantly associated with handedness to date. They found a common variant in the gene PCSK6 (also known as PACE4) that was associated with relative hand skill in a group of individuals with dyslexia. This gene is known to play a key role in the development of left/right asymmetry in the developing embryo, through its interaction with NODAL. Mice who have had PCSK6 knocked-out often develop situs ambiguus (an asymmetry defect where organs develop in abnormal positions). The association was specific to individuals with dyslexia, however, individuals with dyslexia are no more likely to be left- or right-handed. Instead, the researchers suggest that there is a genetic interaction (epistasis) between genes involved in the development of left/right asymmetry, and genes involved in dyslexia. This provides molecular evidence for a link between language development (in this case reading ability), and handedness / brain asymmetry.

The effect of the variant in PCSK6 is consistent with a multi-genic model of handedness, providing further evidence against single-gene theories. As studies become larger and more sophisticated, it is likely that many more variants in multiple genes will be identified that are associated with handedness.

Parental and social pressure

This theory explains right-handed dominance by claiming that since people are mostly right-handed, parental pressure essentially teaches this behavior as normal. In this way, the right-handed dominance continues. This idea assumes that environmental pressures can dominate over a genetic tendency because the percentage of left-handed people has remained virtually unchanged^{[citation needed]}. There are recent studies that indicate no heredity involvement in handedness. On the other hand, however, "...in another study, the handedness of adopted children was not related to the handedness of their adoptive parents, but it was related to the handedness of their biological parents." This may disprove the idea of "teaching" handedness by modeling parental behavior, but more research needs to be done in this area to provide stronger evidence.

Correlations

Intelligence

In his book Right-Hand, Left-Hand, Chris McManus of University College London argues that the proportion of left-handers is increasing and left-handed people as a group have historically produced an above-average quota of high achievers. He says that left-handers' brains are structured differently (in a way that increases their range of abilities) and the genes that determine left-handedness also govern development of the language centres of the brain.

Income

In a 2006 U.S. study, researchers from Lafayette College and Johns Hopkins University concluded that there was no scientifically 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.

Politics

See also: Handedness of Presidents of the United States

Of the seven most recent U.S. Presidents, four, including Barack Obama, have been left-handed, while a fifth is said to have been ambidextrous: Ronald Reagan, who was left-handed by birth, became president after he defeated left-handed candidate George H. W. Bush in the Republican primary election. Four years earlier, Reagan had lost the Republican presidential primary to incumbent left-handed President Gerald Ford. George H. W. Bush succeeded Reagan and later ran for re-election against left-handers Bill Clinton and Ross Perot. Clinton's second term opponents included Perot and Bob Dole, who had become left-handed when his right arm was paralyzed in combat 50 years earlier. After Clinton's term, his left-handed Vice President Al Gore lost to right-handed George W. Bush, who four years later prevailed over John Kerry and John Edwards, both left-handed. Left-handed then-Senator Obama defeated left-handed Senator John McCain in his race for the presidency. Including the 2012 campaign, the last time the United States Presidential Election featured no left-handed candidate from a major political party was 1972.

Handwriting and written language

The 44th President of the United States, Barack Obama, is left-handed as were Presidents Clinton, George H. W. Bush, Reagan, and Ford.

Writing when moving one's hand away from its side of the body can cause smudging if the outward side of the hand is allowed to drag across the writing, it is considered easier to write ABC... and other left-to-right-scripts with the right hand than with the left. Left-handed people who use Arabic, Persian, Urdu, Hebrew or any other right-to-left script do not have the same difficulties with writing - the right-to-left nature of these scripts prevents left-handers from running their hand on the ink as happens with left-to-right languages.

Left-to-right alphabets can be written smudge-free, and in proper "forward slant" with the left-hand, if the paper is turned 45 degrees clockwise (the left-hand is then drawn toward the body on forward strokes). This prevents the painful bent-wrist "crab hand" often seen in left-handed writers, and it permits a clear view of what has already been written on the current line. It is also possible to do calligraphy in this posture with the left-hand, but using right-handed pen nibs. Otherwise, left-handed pen nibs are required in order to get the thick-to-thin stroke shapes correct for most styles, and the left-handed calligrapher is very likely to smudge the text. Left-handed pen nibs are not generally easy to find, and strokes may have to be done backwards from traditional right-handed calligraphic work rules to avoid nib jamming and splatter. Left-handed people have an advantage in writing 19th-century copperplate hands, which control line-width by pressure on the point.^{[citation needed]}

These issues have been made almost irrelevant by the near-universal adoption of fast-drying ballpoint and gel pens for everyday use (pen nibs are now a specialty item rarely stocked by office suppliers), and the widespread use of computers and other electronic devices for communicative purposes.

Social stigma and repression of left-handedness

Main article: Bias against left-handed people

Left-handed people live in a world dominated by right-handed people and many tools and procedures are designed to facilitate use by right-handed people, often without even realising difficulties placed on the left-handed. "For centuries, left-handers have suffered unfair discrimination in a world designed for right-handers." However, as well as inconvenience, left-handed people have 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. The Latin word sinistra meant "left" as well as "unlucky" and this double meaning survives in European derivatives of Latin, and in the English word "sinister.'

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 considered one that is unflattering or dismissive in meaning. 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.

Black magic is sometimes referred to as the "left-hand path".

Until very recently in Taiwan, left-handed people were strongly encouraged 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. Because writing when moving one's hand away from its 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 is less feasible with the left hand than the right. Conversely, right-to-left alphabets, such as the Arabic and Hebrew, are generally considered easier to write with the left hand in general.

Left Handers' Day, August 13, 2002

Negative associations of language

Historically, the left side, and subsequently left-handedness, was considered negative in many cultures. The Latin word sinistra originally meant "left" but took on meanings of "evil" or "unlucky" by the Classical Latin era, and this double meaning survives in Italian, and in the English word "sinister". Alternatively, sinister comes from the Latin word sinus meaning "pocket": a traditional Roman toga had only one pocket, located on the left side. The right hand has historically been associated with skill: the Latin word for right-handed is dexter, as in "dexterity", meaning manual skill. Even the word "ambidexterity" reflects the bias. Its intended meaning is "skillful on both sides". However, since it keeps the Latin root dexter, which means "right", it ends up conveying the idea of being "right-handed at both sides". This bias is also apparent in the lesser-known antonym "ambisinistrous", which means "clumsy on both sides". In more technical contexts, "sinistral" may be used in place of "left-handed" and "sinistrality" in place of "left-handedness".

Meanings gradually developed from use of these terms in the ancient languages. In many modern European languages, including English, the word for the direction "right" also means "correct" or "proper", and also stands for authority and justice. In most Slavic languages the root prav is used in words carrying meanings of correctness or justice.

The French word gauche ("left") means clumsy, graceless or awkward, and adroit (related to droit, "right") means "dextrous". These secondary meanings have entered English.

The Dutch expression "twee linkerhanden hebben" ("to have two left hands") indicates clumsiness, as well as the Hungarian expression "kétbalkezes" ("one with two left hands"). Modern Israeli Hebrew uses the same expression ("שתי ידיים שמאליות", "two left hands"), or sometimes even "ארבע ידיים שמאליות" ("four left hands", for extreme clumsiness). In the United Kingdom someone who is a poor dancer would commonly be described as "having two left feet".

In Chinese culture, the adjective "left" (Chinese: 左; pinyin: zuǒ) sometimes means "improper" or "out of accord". For instance, the phrase "left path" (Chinese: 左道; pinyin: zuǒdào) stands for unorthodox or immoral means.

In Portuguese, "direito" (right) stands for the doing something correctly as well as for Law School. The expression "acordar com o pé direito" (waking up on your right foot) means that the person woke up in a good mood, while "acordar com o pé esquerdo" (waking up on your left foot) means waking up in a bad mood.

In colloquial Russian, "левый" (left) means "unauthorised", "under the table", and "ходить налево" ("to go leftwards") is to commit adultery.

In ancient Hebrew, as well as in other ancient Semitic and Mesopotamian languages, the term "left" was a symbol of power or custody. The left hand symbolized the power to shame society, and was used as a metaphor for misfortune, natural evil, or punishment from the gods. This metaphor survived ancient culture and was integrated into mainstream Christianity by early Catholic theologians, such as Ambrose of Milan, to modern Protestant theologians, such as Karl Barth, to attribute natural evil to God in explaining God's omnipotence over the universe.

In Turkish "sağ" (right) also means "alive".

When it is said that a person has slept on their left side in the Akan language of Ghana, it means the person is dead. The use of the left hand in everyday activities such as eating, cooking, writing and pointing are strongly discouraged. It is an insult to shake hands or greet a person with the left hand. It is also inappropriate to shake hands with a group of people beginning from the left side and any exchanges between people such as giving or receiving an item must be done with the right hand. The use of the left hand is, however, encouraged in handling unsanitary items such as a chamber pot and excreta.

There are many colloquial terms used to refer to a left-handed person, e.g. "southpaw" or "goofy" (USA). Some are just slang or jargon words, while other references may be offensive or demeaning, either in context or in origin. In some parts of the English-speaking world, "cack-handed" is slang for left-handed, and is also used to mean clumsy. The origin of this term is disputed, but some suggest it is derived from the Latin cacare, in reference to the habit of performing ablutions with the left hand, leaving the right hand "clean". However, other sources suggest that it is derived from the Old Norse word keikr, meaning "bent backwards". Some Australians use "cacky-handed". An alternative Australian slang word for a left-handed individual is the term Molly-Duker.

Positive connotations

Lloque Yupanqui, the third Sapa Inca, whose name means "the glorified lefthander"

Among Incas, left-handers were called (and now are called among the indigenous peoples of the Andes) lloq'e (Quechua: lluq'i), which has positive value. Indigenous peoples of the Andes consider that left-handers possess special spiritual abilities, including magic and healing.

The Third Sapa Inca—Lloque Yupanqui—was left-handed. His name when translated from Quechua means "the glorified lefthander". However, many linguists fluent in the native Quechua language, commonly translate Lloque Yupanqui as "The Unforgettable Left-Handed One".^{[citation needed]}

In China and Japan, the formula "man left, woman right" (男左女右, nán zuǒ, nǚ yòu) expresses the traditional concept that the left is the yang (阳, yáng) direction and side of the body. The character for "left", 左, also depicts a left hand attending to its work. In contrast, the character for "right", 右 (yòu), depicts a right hand in relation to the mouth, suggesting the act of eating.^{[citation needed]}

In Tantric Buddhism, the left hand represents wisdom.^{[citation needed]}

In early Roman times, the left side retained a positive connotation, as the Augures proceeded from the eastern side. The negative meaning was subsequently borrowed into Latin from Greek, and ever since in all Roman languages.

In Russian, "levsha" (lefty, lefthander) became a common noun for skilled craftsman, after the title character from "The Tale of Cross-eyed Lefty from Tula and the Steel Flea" written in 1881 by Nikolai Leskov.

The Boy Scouts shake hands left-handedly, since the left hand is closer to the heart (considering the heart as the classical seat of emotions, including love).

Similarly, the comic strip hero The Phantom wears a ring on his left hand that bears a symbol connoting goodness and protection.

Accessibility of implements and skills

left-handed (left) and right-handed (right) scissors

Kitchen knives: (1) symmetrical, (2) right-handed, (3) left-handed

People tend to have most strength and control in their lead hand—whether left or right. Because the vast majority of the world population is right-handed, most everyday items are mass-produced for expected use with the right hand. Tools, game equipment, musical instruments and other items must be specially ordered for left-handed use, if they are available at all.

Right-handed tools may be difficult or uncomfortable to use for the left-handed unless they have learned to adjust. For example, (right-handed) scissors are arranged so that the line being cut along can be seen by a right-handed user, but is obscured to a left-handed user. Furthermore, the handles are often molded in a way that is difficult for a left-hander to hold, and extensive use in such cases can lead to varying levels of discomfort. Ambidextrous scissors will mold the handles to be the same shape, but will not reverse the position of the blades. Most importantly, the scissoring or shearing action that causes the scissors to cut often depends on how the blades work together. Right handed use causes the blades act one against the other resulting in a cutting effect. A left handed person operating a pair of right-handed scissors may tend to force the blades apart from each other, resulting in a gap between the blades instead of contact, which may reduce the effectiveness of the scissors to zero. Left-handed scissors require inverting both the handles and the blades if the left-handed user is to fully see the progress of the cut. Right-handed scissors place the thumb's blade on the left side, while left-handed scissors have this on the right side. This ensures the left hand's motion draws the blades together while cutting, ensuring a cleaner cut.

Other handed items which could prove to be inconvenient for left-handers include circular saws, tin snips, cameras, train-station turnstiles, can openers, potato peelers, corkscrews, rulers, computer mice and keyboards, watches, chequebooks, spiral notebooks, lever arch files, fishing reels, golf clubs, guitars, boomerangs, measuring cups and pencil sharpeners.

Left-handed adaptations have even bridged the world of music. Left-handed guitars are manufactured as an alternative to using a flipped around right-handed guitar. There have even been inverted pianos where the deepest notes correspond to the rightmost keys instead of the leftmost. Inverted trumpets are made, too. Although the main valves for most brass instruments are designed to be operated with the right hand, the prevailing belief is that left-handed performers are not at a significant disadvantage. The French horn is played with the left hand, and there is no evidence that right-handed performers are at a disadvantage on that instrument.

A left-handed individual may be known as a southpaw, particularly in a sports context. It is widely accepted that the term originated in the United States, in the game of baseball. Ballparks are often designed so that batters are facing east, so that the afternoon or evening sun does not shine in their eyes. This means that left-handed pitchers are throwing with their south-side arm. The Oxford English Dictionary lists a non-baseball citation for "south paw", meaning a punch with the left hand, as early as 1848, just three years after the first organized baseball game, with the note "(orig. U.S., in Baseball)." A left-handed advantage in sports can be significant and even decisive, but this advantage usually results from a left-handed competitor's unshared familiarity with opposite-handed opponents. Baseball is an exception since batters, pitchers, and fielders in certain scenarios are physically advantaged or disadvantaged by their handedness. An odd discrepancy where the left-handed athlete is not at a disadvantage is ice hockey, where there are significantly more left-shooters than right. Although it should be noted that left-shots are not always left-handed, and vice versa.

A US Navy SEALs left-handed shooter.

The vast majority of firearms are designed for right-handed shooters, with the operating handle, magazine release, and/or safety mechanisms set up for manipulation by the right hand, and fired cartridge cases ejected to the right. Also, scopes and sights may be mounted in such a way as to require the shooter to place the rifle against the right shoulder. A left-handed shooter must either purchase a left-handed or ambidextrous firearm (which are manufactured in smaller numbers and are generally more expensive and/or harder to obtain), shoot a right-handed gun left-handed (which presents certain difficulties, such as the controls being improperly located for the left hand or hot shell cases being ejected towards the shooter's body, especially the eyes or down the collar or right sleeve), or learn to shoot right-handed (which may be less comfortable, feel "unnatural", and probably less effective). A related issue is ocular dominance, due to which left-handed people may wish to shoot right-handed, and vice versa.

Lever action and pump action firearms present fewer difficulties for left-handers than bolt action weapons do. Many weapons with adjustable sights allow for left-handed use, but for a right eye dominant shooter it is necessary to adjust. In fact, most weapons adjust well enough that a weapon will not eject shells into a left-hander's eye. However, some bullpup style rifles, such as the L85, cannot be safely fired left-handed at all, being that the empty cases would be ejected directly at the shooter's face.

Power tools, machinery and other potentially dangerous equipment is typically manufactured with the right-handed user in mind. Common problems faced by left-handed operators include the inability to keep materials steady, and difficulty reaching the on/off switch, especially in emergency situations. A further factor is the relative strength of the lead hand and arm. A left handed person will tend to have less physical strength in the right hand and arm, and vice versa. So while heavy tools may necessarily have to be held in the right hand due to the handed-ness of the tool, there will be less strength in a left handed person to control and guide the tool.

Also, in some countries classrooms and offices are designed to maximize the use of natural light by placing desks so that the windows are on the left. This often creates inconveniences for left-handers as the shadow of their left hand with the pen makes it harder to see the text being written.

One of the few items in common use that is actually advantageous for left-handers is the QWERTY keyboard. Over 3,000 words in English can be typed with only the left hand on the QWERTY board as opposed to some 300 with the right hand, and overall, 56% of the keystrokes made when touch-typing on a QWERTY board are made with the left hand.

In countries with right-hand drive vehicles, left-handers benefit from having more of the delicate dashboard controls being managed by their dominant hand, as well as the gearstick when driving a manual transmission vehicle.

A reverse-style watch has hands that move counter-clockwise.   Close-up of a guitar made for a left-handed person.   Pitcher John Danks throwing left-handed.   Left-handed Remington 700 rifle action—note that the bolt handle is not visible from this side.   A table saw. Notice how the cutting surface, fence, etc. are on the right side.

See also

In general

• Cross-dominance
• Footedness
• Ocular dominance (eyedness)
• Laterality
• Chirality (chemistry)
• Chirality (mathematics)
• Chirality (physics)

Handedness

• Edinburgh Handedness Inventory
• Handedness of Presidents of the United States
• Musicians who play left-handed
• Handedness and sexual orientation
• Handedness and mathematical ability
• Geschwind–Galaburda hypothesis
• Situs inversus
• Southpaw stance (boxing)

Sources

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) ‘Left-handed Children’, Debate contribution by the Rt Hon. Mr. Peter Luff (MP for Mid-Worcestershire), House of Commons, 22 July.
• Is your Child Left-Handed? Why, according to psychological tests, left-handed people ought to remain so. Popular Science. December 1918. p. 22. http://books.google.com/books?id=EikDAAAAMBAJ&pg=PA22.
• Handedness and Earnings / Higher paychecks: a left-handed compliment?
• Handedness & earnings, published in Journal of Human Resources 2007

UpToDate Contents

全文を閲覧するには購読必要です。 To read the full text you will need to subscribe.

• 1. 右室心筋梗塞 right ventricular myocardial infarction
• 2. 不整脈原性右室心筋症の臨床症状および診断 clinical manifestations and diagnosis of arrhythmogenic right ventricular cardiomyopathy
• 3. 右心の心エコー評価 echocardiographic assessment of the right heart
• 4. 右脚ブロック right bundle branch block
• 5. 不整脈原性右室心筋症の治療および予後 treatment and prognosis of arrhythmogenic right ventricular cardiomyopathy

English Journal

• "Crossed" somatoparaphrenia: an unusual new case and a review of the literature.

• Perren F1, Heydrich L, Blanke O, Landis T.
• Experimental brain research.Exp Brain Res.2015 Jan;233(1):175-9. doi: 10.1007/s00221-014-4101-z. Epub 2014 Oct 10.
• Somatoparaphrenia is a delusional misidentification and confabulation of body parts, usually arm or hand, opposite to a cerebral lesion, generally of the "minor" right hemisphere. There is some controversy concerning lesion site (fronto-parietal; parieto-temporal; posterior insula, additional subcor
• PMID 25300957

• Praxis and writing in a right-hander with crossed aphasia.

• Falchook AD1, Burtis DB, Acosta LM, Salazar L, Shushrutha Hedna V, Khanna AY, Heilman KM.
• Neurocase.Neurocase.2014 Jun;20(3):317-27. doi: 10.1080/13554794.2013.770883. Epub 2013 Apr 5.
• Studies of patients with brain lesions have demonstrated that language and praxis are mediated by dissociable networks. However, language has the capacity to influence the selection of purposeful actions. The abilities to use language and to program purposeful movements are often mediated by network
• PMID 23557340

• [Relation between shoulder impingement syndrome and club head velocity in high-performance amateur golfers].

• Ostreicher M1, Schwarz M.
• Sportverletzung Sportschaden : Organ der Gesellschaft für Orthopädisch-Traumatologische Sportmedizin.Sportverletz Sportschaden.2013 May;27(2):108-11. doi: 10.1055/s-0033-1335519. Epub 2013 May 27.
• BACKGROUND: Joint structure damages due to overstrain often occur even in commonly not injury-prone golfing. Triggered by the golf swing's repetitive movement pattern and technique deficits of the player these structural damages are most likely to affect the lumbar spine as well as shoulder and elbo
• PMID 23712389

Japanese Journal

• 3D Motion Analysis Comparison of the Dominant Hand Wrist Flexion during Writing

• Journal of Physical Therapy Science 24(10), 1013-1015, 2012
• NAID 130004431773

• 左前頭葉梗塞で foreign accent syndrome を呈した矯正右利きの一例

• 高次脳機能研究 : 日本高次脳機能障害学会誌 = Higher brain function research 31(2), 205-211, 2011-06-30
• NAID 10031128152

• 左前頭葉梗塞で foreign accent syndrome を呈した矯正右利きの一例

• 高次脳機能研究 （旧 失語症研究） 31(2), 205-211, 2011
• NAID 130004467684

Related Links

• right-handerの意味 - goo辞書 英和和英

right-handerとは。意味や和訳。[名詞]1 右利きの人，(特に野球の)右腕投手.2 ((話))(1)右手打ち，右パンチ.(2)(バスケットボールなどで)右手投げ，右手トス.3 (道などの)右折部.[語源]1857 - 80万項目以上収録、例文・コロケーションが豊富な ...

• Right-hander - definition of right-hander by The Free Dictionary

right-hand·er (rīt′hăn′dər) n. One who is right-handed. right-hander n 1. (Boxing) a blow with the right hand 2. a person who is right-handed right′-hand′er n. 1. a right-handed person. 2. a blow or pitch delivered with the right hand.

Related Pictures

---

★リンクテーブル★

関連記事	「right」「hand」「rig」

「right」

　　[★]

• n.

• 右、権利

• adj.

• 正しい、右位の、直角の

関

correct、dexter、dextroposition、fair、human right、rectangular、right angle

　 　 　 　 　 　 　 　 　 　 　 　 　 　 　 　 　 　 　 　 　 　 　 　 　 　

「hand」

　　[★] 手 　 　 　 　 　 　 　 　 　 　 　 　 　

「rig」

　　[★]