User:Samanthav321/sandbox/assignment

From Wikipedia, the free encyclopedia
This page 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).

{{Multiple issues | cleanup-rewrite=January 2011 | weasel=August 2011| {{POV|date=July 2012}} }} 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 or a (informally) righty and one who is more skilled with the left is said to be left-handed or a lefty. The majority of infants develop hand preference by 6 months of age.[1] A minority of adult people are equally skilled with both hands, and are termed ambidextrous. Handedness is one example of body laterality.

Different types[edit]

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.[2][3]
  • 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 10-30% of the world population is left-handed.[4]
  • Mixed-handedness, also known as cross-dominance, means 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 accurately with their right. The percentage of mixed-handed people is difficult to determine because it is a matter of degree, and because many people define handedness by the hand used for writing. Most left-handed people develop some mixed-handedness simply by living in a world where most everyday objects are designed for right-handed people, or by growing up with right-handed parents; for example, some tools may force mixed-handedness (e.g., scissors with handles shaped for the right hand).
  • 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 favour 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.

A modern scientific view of handedness is that it is not a simple preference for one hand because the two hands actually work together in more subtle ways.[5][6] For example, when a right-handed person is writing, the left hand is involved in important ways: it orients and grips the paper to help the right hand operate. In this example the right hand provides finer movements and the left broader, contextual movements.

Theories of handedness developing from non-handedness[edit]

See also: Lateralization of brain function and Laterality

Brain hemisphere division of labor[edit]

Division of labor is a 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, allowing for a smaller and less energy-consuming brain. Since in most people, the left side of the brain controls speaking and also controls the right hand, this would explain why most people are right-handed.[citation needed]

Some researchers have suggested that handedness may have developed through the advantage of improved throwing ability, and that language lateralization developed later. Another suggestion is that infant carrying on a particular side of the body allowed the other side to specialize on other tasks.[7]

The "division of labour" theory doesn't explain why left-handed people don't all have a reversed brain specialization.[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. About 25% of left-handed people use both sides of the brain equally.[8]

Also not explained is why one brain orientation is much more common than the other, instead of both hemispheres being equally likely to be the dominant one regarding language or dexterity. Scientists are asking this laterality question about other body functions as well, such as the position of organs in the chest and abdomen.[citation needed]

Theories of left-handedness vs. right-handedness[edit]

The prevalence of right-handedness is universal across human cultures, although the percentage of right-handedness is smaller in primitive cultures.[9] Chimpanzees have a similar pattern with right-handedness being more common.[7]

Some studies have shown that preferences for one hand or one body side occur in the womb and in newborns and infants and are associated with later handedness.[8] Hand orientation in fetuses is most commonly determined by observing which hand is usually held close to the mouth.[10] Physician Ernst Heinrich Weber studied handedness in the nineteenth century; he believed that the preponderance of right-handedness results indirectly from the positions of internal organs, such as the heart on the left.[11]

Possible advantages of left-handedness[edit]

Some studies have shown, as John Santrock points out, 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." 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.[8] However, Hardyck and Petrinovich[12] reviewed a large amount of literature and found no overall differences in mental ability in right-handers and non-right-handers.

Other reported associations with left-handedness include higher creativity, a larger corpus callosum, certain right brain regions being larger, shorter transfer time of information between hemispheres, and higher socioeconomic status.[7]

Possible disadvantages of left-handedness[edit]

Although there isn't much difference in children's school performance in regard to handedness, some studies have found that 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.[8] Also, in languages such as English which are written left-to-right, left-handed writers may write more slowly, taking care not to smudge their writing when moving their hands across the page. 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.[7]

Left-handedness and close combat[edit]

An evolutionary psychology explanation of why right-handedness is more common today starts by suggesting that, in the ancestral environment, there would have been more disadvantages than advantages from left-handedness regarding overall inclusive fitness (leaving of descendants); there is no evidence whatsoever for this type of adaptiveness. 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. For example, left-handed fighters sometimes had an advantage in close combat because right-handed people were unfamiliar with fighting the rare left-handed opponents, while left-handed people were more familiar with fighting right-handed opponents.[7]

A 2004 study by Charlotte Faurie and Michel Raymond, of the University of Montpellier II in France, found strong support for the idea that, at least in primitive societies with higher levels of violence, left-handed people are more numerous. They related this to the success of left-handers in certain sports.[13][14]

This theory may also explain why left-handedness is more common in men than in women.[7]

Right-handedness may be more common, because learning to use tools is easier when the hand on the same side as the demonstrator's hand is used to perform the action that is learned. Right-handedness also being more common in chimpanzees suggests this advantage took root in a common ancestor. In this case a mere coincidental difference in frequency of handedness might have been key to the adaptivity of the right-handed variant.

Left-handedness and sports[edit]

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.[7]

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.[citation needed]

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).[citation needed]
  • In baseball, a right-handed pitcher's curve ball will break away from a right-handed batter and towards a left-handed batter. Historical batting averages show that left-handed batters have a slight advantage over right-handed batters when facing right-handed pitchers.[15] 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.[16] Sixteen of the top twenty career batting averages in Major League Baseball history have been posted by left-handed batters.[17] 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.[18]
  • Because a left-handed pitcher faces first base when he is in position to throw to the batter, whereas a right-handed pitcher has his back to first base, a left-handed pitcher has an advantage when attempting to pickoff baserunners at first base.[18]
  • 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.[19] 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.[20] A left-handed catcher would have a potentially more dangerous time tagging out a baserunner trying to score.[20] 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.[20] The lack of left-handed catchers might be due to traditions and to the fact that left-handed catcher's mitts are almost non-existent and unavailable for young players.[20]

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.[citation needed]

Hormones[edit]

Prenatal hormone imbalances may play a role in left-handedness. While the Geschwind–Galaburda testosterone hypothesis is often cited as cause, there is no evidence to support this.[citation needed] Recently, research has emerged suggesting that high prenatal estrogen exposure may play a role. 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.[21] Increased prenatal estrogen exposure in men, and its left-handed effect, may induce lower visual-spatial skills.[22]

Environmental influences before and at birth (to be seen in the context of the new genetic discovery)[edit]

Birth stress[edit]

The "pathological left-hander" theory's basic premise is that left-handedness is due to brain damage during the birth process.[23] However, there is no hard evidence and genetic causes are thought to be more important.[24]

Prenatal vestibular asymmetry[edit]

Previc[9] after reviewing a large number of studies, found evidence that the position of the fetus 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[9] 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,[25] and asymmetry of the vestibular cortex is strongly correlated with the direction of handedness.[26]

Ultrasound[edit]

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.[27][28]

Twins theory[edit]

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[29] 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.[30]

Genetic factors[edit]

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.[31] A large study of twins from 25,732 families by Medland et al. (2006) has indicated that the heritability of handedness is 24%.[32] This leaves about three quarters of the effect to be explained by environmental factors.

To date, two theoretical single gene models have been proposed to explain the patterns of inheritance of handedness, the first by Dr. Marian Annett[33] of the University of Leicester and the second by Professor Chris McManus[31] 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.[34]

Although single-gene models can be fitted to the data, a number of genetic linkage studies have been performed, all of which have provided evidence for different regions of the genome contributing to variation in handedness.[35][36][37][38] Only one of these studies has led to the identification of a specific gene that is proposed to contribute to variation in handedness.[39][40]

Medland et al.[41] found a gene that is positively correlated with left-handedness in females, and negatively correlated in males. This may help to explain why there are more left-handed men than women (around 12% in men versus 10% in women globally).[42]

Parental and social pressure[edit]

Santrock reports a study in which "...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."[8] 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.[citation needed]

Correlations[edit]

Intelligence[edit]

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, although many scientists agree that there is no real difference in intelligence between the two.[43]

Income[edit]

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.[44]

Politics[edit]

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,[45][46][47] 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[48] and Ross Perot.[47] 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.[49] 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[edit]

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

Because writing when moving one's hand across 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 the Latin alphabet and other left-to-right-scripts with the right hand than with the left. Right-handed people find the same difficulty with right-to-left scripts such as Arabic, Persian, Urdu, or Hebrew.[citation needed]

These issues are of declining importance with the near-universal adoption of fast-drying ballpoint and gel pens for everyday use and the widespread use of computers and other electronic devices for communicative purposes.[citation needed] However, calligraphers still use ink and pen nibs, and left-handers must find a way to write smudge-free. One technique, which gives the proper "forward slant",is to turn the paper 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]

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. Because of 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.

Social stigma and repression of left-handedness[edit]

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 for use by right-handed people, often without considering difficulties placed on the left-handed. "For centuries, left-handers have suffered unfair discrimination in a world designed for right-handers," says Santrock.[8]

At certain times left-handed people have been considered unlucky or even evil for their difference by the right-handed majority.[citation needed]

In some African societies, for example among some Yorubas, inter alia, a left-hander cannot be king.

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.'[citation needed]

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.[citation needed]

Black magic is sometimes referred to as the "left-hand path".[citation needed]

Left Handers' Day, August 13, 2002

Negative associations of language[edit]

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". Interestingly enough, while the Italian word "sinistro" means both "left" and "scary", "creepy", the Italian word for left-handed is "mancino". This word has no negative connotations in modern Italian, and it is also used to denote an astute and unexpected plan or move ("tiro mancino"). 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".[50] In more technical contexts, "sinistral" may be used in place of "left-handed" and "sinistrality" in place of "left-handedness".[51]

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.[citation needed]

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 Persian Farsi, the word "rast" means "right" in both direction and sense of correctness, as in English. It can also mean "direct".

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 Polish, "lewy" (left) means either "illegal" (e.g. on a business), or "not working correctly" (about a device). Same as in Portuguese, the English idiom "wake up on the wrong side of bed" (be in a bad mood) goes "wstać lewą nogą" which literally means "wake up on the left foot", but unlike Portuguese, there's no "waking up on the right foot" in usage. The equivalent of "be all thumbs" (be clumsy) expression is "mieć dwie lewe ręce" (literally: to have two left hands).

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.[52] 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,[53] to modern Protestant theologians, such as Karl Barth,[54] 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.[citation needed]

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".[55][56] However, other sources suggest that it is derived from the Old Norse word keikr, meaning "bent backwards".[57] Some Australians use "cacky-handed". An alternative Australian slang word for a left-handed individual is the term Molly-Duker.[58]

Positive connotations[edit]

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.[citation needed]

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.[59] 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.[citation needed]

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).[citation needed]

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

Accessibility of implements and skills[edit]

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.[citation needed]

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, which have the thumb's blade on the left side, can cause the following problems for left-handed users:

  • The line being cut along can be seen by a right-handed user, but is obscured to a left-handed user. This can be easily overcome when cutting stiff material like paper by holding the sheet upright, but remains a problem with soft material.
  • Handles are often molded for the comfortable use in the right hand; however, there are also ambidextrous scissors which have handles favouring neither hand, and even hybrid scissors which have handles molded for the left hand but maintain a right-handed blade position.[60]
  • The scissoring or shearing action that causes the scissors to cut cleanly depends on the blades being pressed together. In scissors which are sharp and of good quality, with a pressure adjustment screw, the blades hold themselves together. However, if the blades are loose, then in the right hand a downward pressure of the thumb accomplishes this. A left-handed person operating a pair of right-handed scissors must use an upward pressure of the thumb to achieve the same effect. Left-handers who are taught scissoring technique by right-handed people sometimes try to use downward thumb pressure on right-handed scissors, causing a gap between the blades and poor cutting results. For those who use scissors for long periods of time, such as sewers and tailors, the upward thumb technique can be tiring.[60]

True left-handed scissors have both the handles and the blades reversed so that the left-handed user is able to see the progress of the cut clearly and to use the more comfortable downward thumb pressure.[61] However, those who have learned to use only left-handed scissors find themselves with other difficulties:

  • Left-handed scissors will be unavailable in most places, and the user may have to carry a pair.
  • Left-hand scissor sharpeners are rare.[62]
  • Left-handed users have less selection when buying other scissor-like tools (nail scissors, pruning shears, etc.).[63] [citation needed]

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, mechanical watches, chequebooks, spiral notebooks, lever arch files, fishing reels, golf clubs, guitars, boomerangs, measuring cups and pencil sharpeners.[citation needed]

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.[64] 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.[citation needed]

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.[65] Ballparks are often designed so that batters are facing east, so that the afternoon or evening sun does not shine in their eyes.[66] This means that left-handed pitchers[67] are throwing with their south-side arm.[68] The Oxford English Dictionary lists a non-baseball citation for "south paw", meaning a punch with the left hand, as early as 1848,[69] just three years after the first organized baseball game, with the note "(orig. U.S., in Baseball)."[70] 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.[citation needed]

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.[71] 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.[citation needed]

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. [citation needed]

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.[72]

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.[citation needed]

  • Although reversed, this watch has its knob on the right, intended for right-handed wearers.
    Although reversed, this watch has its knob on the right, intended for right-handed wearers.
  • Close-up of a guitar made for a left-handed person.
    Close-up of a guitar made for a left-handed person.
  • Pitcher John Danks throwing left-handed.
    Pitcher John Danks throwing left-handed.
  • Left-handed Remington 700 rifle action—note that the bolt handle is not visible from this side.
    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.
    A table saw. Notice how the cutting surface, fence, etc. are on the right side.

See also[edit]

In general
Handedness

Sources[edit]

  1. ^ Handedness, Time Use and Early Childhood Development, at Institute for the Study of Labor. Authors: David W. Johnston, Manisha Shah, Michael A. Shields (April 2007). Revised version published (with Michael E.R. Nicholls) as 'Nature's Experiment? Handedness and Early Childhood Development' in: Demography, 2009, 46 (2), 281 - 301).
  2. ^ Holder, M. K. (1997). "Why are more people right-handed?". Sciam.com. Scientific American Inc. Retrieved 2008-04-14.
  3. ^ Psychology for A-level second edition, page 309
  4. ^ Hardyck C, Petrinovich LF (1977). "Left-handedness". Psychol Bull. 84 (3): 385–404. doi:10.1037/0033-2909.84.3.385. PMID 859955.
  5. ^ Guiard, Y. (1987). "Asymmetric division of labor in human skilled bimanual action: The kinematic chain as a model". Journal of Motor Behavior. 19 (4): 486–517. doi:10.1080/00222895.1987.10735426. PMID 15136274.
  6. ^ Kabbash, Paul; Buxton, William; Sellen, Abigail (1994). "Two-Handed Input in a Compound Task". Proceedings of CHI '94: 417–423. doi:10.1145/191666.191808. ISBN 0-89791-650-6.
  7. ^ a b c d e f g Diana Widermann, Robert A. Barton, and Russel A. Hill. Evolutionary perspectives on sport and competition. In Roberts, S. C. (2011). "Applied Evolutionary Psychology" (Document). Oxford University Press. doi:10.1093/acprof:oso/9780199586073.001.0001. {{cite document}}: Cite has empty unknown parameters: |pmid= and |pmc= (help); Unknown parameter |editor1-first= ignored (help); Unknown parameter |editor1-last= ignored (help); Unknown parameter |isbn= ignored (help)
  8. ^ a b c d e f Santrock, John W.(2008). Motor, Sensory, and Perceptual Development. Mike Ryan [Ed.], A Topical Approach to Life-Span Development(pgs.172–205). Boston, MA: McGraw-Hill Higher Education.
  9. ^ a b c Previc, F.H. (1991). "A general theory concerning the prenatal origins of cerebral lateralization in humans". Psychological Review. 98 (3): 299–334. doi:10.1037/0033-295X.98.3.299. PMID 1891521.
  10. ^ Hopkins, B., Lems, W., Janssen, B. & Butterworth, G. (1987) Postural and motor asymmetries in newborns. Human Neurobiology 6:153–56
  11. ^ Ursachen und Folgen der Rechtshandigkeit by Ernst Weber, Marhold Halle, 1905, page 116
  12. ^ "Law and mental disorder". Lancet. 1 (8119): 759–61. April 1979. doi:10.1016/S0140-6736(79)91212-1. PMID 85995.{{cite journal}}: CS1 maint: date and year (link)
  13. ^ Onion, Amanda (17 February 2005). "The Left-Handed Advantage". ABC News.
  14. ^ Faurie, C.; Raymond, M. (2005). "Handedness, homicide and negative frequency-dependent selection". Proceedings of the Royal Society B: Biological Sciences. 272 (1558): 25. doi:10.1098/rspb.2004.2926. PMID 15875566.
  15. ^ "2012 Major League Baseball Batting Splits". Baseball Reference. Retrieved 6 March 2013.
  16. ^ "The advantage of batting left-handed". hardballtimes.com. Retrieved 7 March 2013.
  17. ^ "Career Leaders & Records for Batting Average". Baseball Reference. Retrieved 6 March 2013.
  18. ^ a b "First Base Pickoffs for Lefty Pitchers". isport.com. Retrieved 7 March 2013.
  19. ^ Miller, Stuart. "The Decline of Left-Handed First Basemen". The New York Times. Retrieved 7 March 2013.
  20. ^ a b c d "Left Handed Catchers". The Encyclopedia of Baseball Catchers. Retrieved 7 March 2013.
  21. ^ Titus-Ernstoff; et al. (2003). "Psychosexual Characteristics of Men and Women Exposed Prenatally to Diethylstilbestrol". {{cite news}}: Explicit use of et al. in: |last= (help)
  22. ^ Reinisch JM, Sanders SA (March 1992). "Effects of prenatal exposure to diethylstilbestrol (DES) on hemispheric laterality and spatial ability in human males". Horm Behav. 26 (1): 62–75. doi:10.1016/0018-506X(92)90032-Q. PMID 1563729.{{cite journal}}: CS1 maint: date and year (link)
  23. ^ Dr. Stanley Coren (1990). Left-handedness: behavioral implications and anomalies. Elsevier. ISBN 9780080867212. Retrieved July 15, 2011.
  24. ^ The left brain knows what the right hand is doing, http://www.apa.org/monitor/2009/01/brain.html Monitor on Psychology Volume 40, No. 1 January 2009
  25. ^ Nonright-handedness, central nervous system and related pathology, and its lateralization: A reformulation and synthesis.
  26. ^ Dieterich, M.; Bense, S.; Lutz, S.; Drzezga, A.; Stephan, T.; Bartenstein, P.; Brandt, T. (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.
  27. ^ Salvesen, K. A.; Vatten, L. J.; Eik-Nes, S. H.; Hugdahl, K.; Bakketeig, L. S. (1993). "Routine ultrasonography in utero and subsequent handedness and neurological development". British Medical Journal. 307 (6897): 159–64. doi:10.1136/bmj.307.6897.159. PMC 1678377. PMID 7688253.
  28. ^ Kieler, Helle; Axelsson, Ove; Haglund, Bengt; Nilsson, Staffan; Salvesen, Kjell Å. (1998). "Routine ultrasound screening in pregnancy and children's subsequent handedness". Early Human Development. 50 (2): 233–45. doi:10.1016/S0378-3782(97)00097-2. PMID 9483394.
  29. ^ Vanishing twin theory debunked
  30. ^ How New Humans Are Made by Charles E. Boklage
  31. ^ a b McManus, Chris. Right Hand, Left Hand. Phoenix Paperbacks, 2003. Print.
  32. ^ Medland et al. Neuropsychologia (2008) 47:330-337
  33. ^ Annett, M. (2009). "The Genetic Basis of Lateralization". In Sommer, Iris E. C; Kahn, René S (eds.). Language Lateralization and Psychosis. pp. 73–86. doi:10.1017/CBO9780511576744.006. ISBN 9780511576744. {{cite book}}: |journal= ignored (help); Unknown parameter |unused_data= ignored (help)
  34. ^ Crow, TJ (2008 Jul). "The 'big bang' theory of the origin of psychosis and the faculty of language". Schizophrenia Research. 102 (1–3): 31–52. doi:10.1016/j.schres.2008.03.010. PMID 18502103. {{cite journal}}: Check date values in: |date= (help)
  35. ^ Francks, Clyde; Delisi, Lynn E.; Fisher, Simon E.; Laval, Steve H.; Rue, Judith E.; Stein, John F.; Monaco, Anthony P. (2003 Feb). "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. {{cite journal}}: Check date values in: |date= (help)
  36. ^ Van Agtmael, Tom; Forrest, Susan M.; Williamson, Robert (2002 Oct). "Parametric and non-parametric linkage analysis of several candidate regions for genes for human handedness". European Journal of Human Genetics : EJHG. 10 (10): 623–30. doi:10.1038/sj.ejhg.5200851. PMID 12357333. {{cite journal}}: Check date values in: |date= (help)
  37. ^ Warren, Diane M.; Stern, Michael; Duggirala, Ravindranath; Dyer, Thomas D.; Almasy, Laura (1 November 2006). "Heritability and linkage analysis of hand, foot, and eye preference in Mexican Americans". Laterality: Asymmetries of Body, Brain and Cognition. 11 (6): 508–524. doi:10.1080/13576500600761056. PMID 16966240.
  38. ^ Laval, S.H.; Dann, J.C.; Butler, R.J.; Loftus, J.; Rue, J.; Leask, S.J.; Bass, N.; Comazzi, M.; Vita, A.; Nanko, S.; Shaw, S.; Peterson, P.; Shields, G.; Smith, A.B.; Stewart, J.; Delisi, L.E.; Crow, T.J. (1998 September 7). "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. {{cite journal}}: Check date values in: |date= (help)
  39. ^ Francks et al. Molecular Psychiatry (2007) 12:1129-1139
  40. ^ Gene for left-handedness is found, http://news.bbc.co.uk/2/hi/health/6923577.stm, BBC, 31 July 2007
  41. ^ Medland, Sarah E.; Duffy, David L.; Spurdle, Amanda B.; Wright, Margaret J.; Geffen, Gina M.; Montgomery, Grant W.; Martin, Nicholas G. (1 November 2005). "Opposite Effects of Androgen Receptor CAG Repeat Length on Increased Risk of Left-Handedness in Males and Females". Behavior Genetics. 35 (6): 735–744. doi:10.1007/s10519-005-6187-3. PMID 16273319.
  42. ^ Papadatou-Pastou, Marietta; Martin, Maryanne; Munafò, Marcus R.; Jones, Gregory V. (2008 Sep). "Sex differences in left-handedness: a meta-analysis of 144 studies". Psychological Bulletin. 134 (5): 677–99. doi:10.1037/a0012814. PMID 18729568. {{cite journal}}: Check date values in: |date= (help)
  43. ^ Right-Hand, Left-Hand official website Accessed June 2006.
  44. ^ Waldfogel, Joel (August 16, 2006). "Sinister and Rich: The evidence that lefties earn more". Slate.
  45. ^ McManus, Chris (2004). Right Hand, Left Hand: The Origins of Asymmetry in Brains, Bodies, Atoms and Cultures. Harvard University Press. ISBN 978-0-674-01613-2.
  46. ^ Wright, Ed (2007). Left-handed History of the World. Barnes & Noble. ISBN 978-0-7607-8704-5.
  47. ^ a b "A Vast Left-Handed Conspiracy". The Washington Post. 6 July 2008. Retrieved January 2011. {{cite news}}: Check date values in: |accessdate= (help)
  48. ^ "Another left-handed president? It's looking that way". Pittsburgh Post-Gazette. February 2008. Retrieved January 2011. {{cite news}}: Check date values in: |accessdate= (help)CS1 maint: date and year (link)
  49. ^ "Four Out of Five Recent Presidents Are Southpaws". ABC News. February 2008. Retrieved January 2012. {{cite web}}: Check date values in: |accessdate= (help)CS1 maint: date and year (link)
  50. ^ "Ambisinistrous". YourDictionary.com. Retrieved November 28, 2003.[dead link]
  51. ^ "Sinistral". YourDictionary.com. Retrieved June 2006. {{cite web}}: Check date values in: |accessdate= (help)[dead link]
  52. ^ Hamilton, Jeffries (1992). Social Justice and Deuteronomy: the Case of Deuteronomy 15. Atlanta: Scholar's Press. p. 145.
  53. ^ Ambrose of Milan: political letters and speeches / translated with an introduction and notes by J.H.W.G. Liebeschuetz. Liverpool, England: Liverpool University Press. 2005.
  54. ^ Ruether, Rosemary Radford (1968–69). "The Left Hand of God in the Theology of Karl Barth--Karl Barth as a Mythopoeic Theologian". The Journal of Religious Thought. {{cite web}}: Missing or empty |url= (help)
  55. ^ "Cack-handed". world wide words.
  56. ^ "Definition of "cack-handed"". The Free Dictionary.
  57. ^ "Cack-handed". Merriam Webster Dictionary.
  58. ^ Quinion, Michael (2003). "Mollydooker". World Wide Words. Retrieved 31 October 2008.
  59. ^ "sinistro" (in Italian). Etimologia. Retrieved January 2011. {{cite web}}: Check date values in: |accessdate= (help)
  60. ^ a b Cowan, Salley, Left Handed Sewing, Courier Dover Publications, 1984, p. 10
  61. ^ Threads Sewing Guide: A Complete Reference from America's Best-Loved Sewing Magazine, Taunton Press, 19 Apr 2011, p. 25
  62. ^ Popular Science, Vol. 185, No. 4
  63. ^ Squire, David, The Pruning Specialist, New Holland Publishers, 2003, p. 10
  64. ^ "The First Left-Handed Piano".
  65. ^ "Southpaws: Doing It Right the Wrong Way". fightbeat.com. Retrieved August 2006. {{cite web}}: Check date values in: |accessdate= (help)[dead link]
  66. ^ "Rules of Major League Baseball, Section 1.04" (PDF). MLB.com.
  67. ^ See also: Warren Spahn Award, which is given annually to the best left-handed pitcher in Major League Baseball.
  68. ^ Olmert, Michael (1996). Milton's Teeth and Ovid's Umbrella: Curiouser & Curiouser Adventures in History. New York: Simon & Schuster. p. 108. ISBN 0-684-80164-7.
  69. ^ Morris, Evan (1995). "Word detective research". Retrieved June 2006. {{cite web}}: Check date values in: |accessdate= (help)
  70. ^ "Definition for "southpaw"". Oxford English Dictionary Online. {{cite web}}: Missing or empty |url= (help)
  71. ^ "Finding Power Tools for Left Handed People". Great Home Improvements. Retrieved 14 January 2011.
  72. ^ "The Curse of QWERTY", Jared Diamond, Discover magazine, April 1997

External links[edit]

Look up assignment in Wiktionary, the free dictionary.
Wikimedia Commons has media related to Left-handedness.

Category:Chirality Category:Discrimination Category:Mental processes

Retrieved from "https://en.wikipedia.org/w/index.php?title=User:Samanthav321/sandbox/assignment&oldid=1192842642"