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== Correlations ==
== Correlations ==
===Intelligence===
===Intelligence===
In his book ''Right-Hand, Left-Hand'',<ref>[http://www.righthandlefthand.com/ Right-Hand, Left-Hand official website] Accessed June 2006.</ref> 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.
In his book ''Right-Hand, Left-Hand'',<ref>[http://www.righthandlefthand.com/ Right-Hand, Left-Hand official website] Accessed June 2006.</ref> 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 champions. 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.


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.<ref>"[http://www.slate.com/id/2147842 Sinister and Rich: The evidence that lefties earn more]", by Joel Waldfogel. Appeared in ''[[Slate (magazine)|Slate]]'' on August 16, 2006.</ref>
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.<ref>"[http://www.slate.com/id/2147842 Sinister and Rich: The evidence that lefties earn more]", by Joel Waldfogel. Appeared in ''[[Slate (magazine)|Slate]]'' on August 16, 2006.</ref>

Revision as of 12:20, 1 September 2011

"Leftie" redirects here. For the political term, see Left-wing politics.
"Southpaw" redirects here. For other uses, see Southpaw (disambiguation).
A person writing the German word "Linkshänder" (left-hander) with the left hand

Left-handedness (also known as sinistrality, sinistromanuality, or mancinism) is the preference for the left hand over the right for everyday activities such as writing. In ancient times it was seen as a sign of the devil, and was abhorred in many cultures. A variety of studies suggest that 10% of the world population is left-handed.[1]

Causes

Main article: Handedness
  • Hand orientation is developed in fetuses, most commonly determined by observing which hand is predominantly held close to the mouth.[2]
  • In 2007, researchers discovered that specific alleles of at least one of three single-nucleotide polymorphisms upstream of the already known LRRTM1 gene were linked to left-handedness.[3][4]
  • 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 have debunked[5] the related Vanishing twin theory, it is yet unexplained why twin children have a high frequency of left-handedness / right-handedness in the pair.[6]
  • Long-term impairment of the right hand: people with long-term impairment of the right hand are more likely to become left-handed, even after their right hand heals.[citation needed]
  • Testosterone: Presence of high levels of testosterone before birth can lead to a left-handed child. This is the Geschwind theory, named after the neurologist who proposed it, Norman Geschwind. It suggests that variations in levels of testosterone during pregnancy shape the development of the fetal brain. Testosterone suppresses the growth of the left cerebral hemisphere and so more neurons migrate to the right hemisphere[citation needed]. The highly developed right hemisphere is now better suited to function as the center of language and handedness. The fetus is more likely to become left-handed, since the right hemisphere controls the left half of the body. The theory goes on to tie the exposure to higher levels of testosterone and the resultant right-hemisphere dominance to a higher risk of auto-immune disorders, learning disorders, dyslexia, and stuttering, as well as higher spatial ability compared with right-handed people.

Social stigma and repression

Main article: Bias against left-handed people
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 European derivatives of Latin, 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".[7] In more technical contexts, "sinistral" may be used in place of "left-handed" and "sinistrality" in place of "left-handedness".[8]

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.

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 Hebrew, as well as in other ancient Semitic and Mesopotamian languages, the term "left" was a symbol of power or custody.[9] 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,[10] to modern Protestant theologians, such as Karl Barth,[11] to attribute natural evil to God in explaining God's omnipotence over the universe.

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".[12][13] However, other sources suggest that it is derived from the Old Norse word keikr, meaning "bent backwards".[14] Some Australians use "cacky-handed". An alternative Australian slang word for a left-handed individual is the term Molly-Duker.[15]

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 (Template:Lang-qu) 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.

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.[16] 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.

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.

Many left-handers adapt themselves well to a right-handed world. Whilst writing may necessarily remain with most a left handed function necessitating a considerable degree of control, other two handed functions may well be done in a right handed manner (eg: holding cricket and baseball bats, golf clubs, holding both knives and forks when eating). Left-handedness will always be far more apparent in one-handed operation (eg: tennis rackets, table tennis bats, javelin throwing, Ball and shot throwing etc.)

Right-handed tools may be difficult or uncomfortable to use for some people who are left-handed unless they have learnt 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. So-called "ambidexterous" 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 - how the blades work together (how they are attached at the pivot) - operates correctly for a right-hander, but some left-handers may tend to force the blades apart rather than shearing the target substance.[17] 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 cameras, train-station turnstiles, can openers, potato peelers, corkscrews, rulers, computer mice and keyboards, watches, chequebooks, spiral notebooks, fishing reels, 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.[18] Inverted trumpets are made, too. Although most brass instruments' main valves 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.[19] Ballparks are often designed so that batters are facing east, so that the afternoon or evening sun does not shine in their eyes.[20] This means that left-handed pitchers are throwing with their south-side arm.[21] The Oxford English Dictionary lists a non-baseball citation for "south paw", meaning a punch with the left hand, as early as 1848,[22] just three years after the first organized baseball game, with the note "(orig. U.S., in Baseball)."[23] 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.

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.[24] 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 whilst 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.

Handheld circular saws are made almost exclusively for right-handers, with the motor and grip on the right side. If held in the left hand, it is impossible for the operator to see what they are cutting and sawdust will be thrown out to the right towards the face and eyes, rather than away from it. Tool manufacturer Porter-Cable produces a left-handed circular saw that can be purchased relatively inexpensively.[24]

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.

  • A reverse-style watch has hands that move counter-clockwise.
    A reverse-style watch has hands that move counter-clockwise.
  • 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

Handwriting and written language

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

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, it is considered easier to write the Latin alphabet with the right hand than with the left. Furthermore, it is considered more difficult to write legible Chinese characters with the left hand than it is to write Latin letters, though difficulty is subjective and depends on the person in question.[25] Left-handed people who speak 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 languages 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 1/4 turn clockwise (90 degrees to the right), and the left hand is drawn toward the body on forward strokes, and left to right on upward strokes (as expressed in directionality of the text). 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 "fonts", 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 learning 19th-century copperplate hands, which control line-width by pressure on the point.

Correlations

Intelligence

In his book Right-Hand, Left-Hand,[26] 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 champions. 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.

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.[27]

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,[28][29][30] 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[31] and Ross Perot.[30] 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. Obama defeated left-handed Senator John McCain in his race for the presidency.[32]

See also

Notes

  1. ^ Hardyck C, Petrinovich LF (1977). "Left-handedness". Psychol Bull. 84 (3): 385–404. doi:10.1037/0033-2909.84.3.385. PMID 859955.
  2. ^ Hopkins, B., Lems, W., Janssen, B. & Butterworth, G. (1987) Postural and motor asymmetries in newborns. Human Neurobiology 6:153–56
  3. ^ Francks et al. Molecular Psychiatry (2007) 12:1129-1139
  4. ^ Gene for left-handedness is found, http://news.bbc.co.uk/2/hi/health/6923577.stm, BBC, 31 July 2007
  5. ^ Vanishing twin theory debunked
  6. ^ How New Humans Are Made by Charles E. Boklage
  7. ^ "Ambisinistrous". YourDictionary.com. Retrieved November 28, 2003.
  8. ^ "Sinistral". YourDictionary.com. Retrieved June 2006. {{cite web}}: Check date values in: |accessdate= (help)
  9. ^ Hamilton, Jeffries (1992). Social Justice and Deuteronomy: the Case of Deuteronomy 15. Atlanta: Scholar's Press. p. 145.
  10. ^ 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.
  11. ^ 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)CS1 maint: date format (link)
  12. ^ "Cack-handed". world wide words.
  13. ^ "Definition of "cack-handed"". The Free Dictionary.
  14. ^ "Cack-handed". Merriam Webster Dictionary.
  15. ^ Quinion, Michael (2003). "Mollydooker". World Wide Words. Retrieved 31 October 2008.
  16. ^ "sinistro" (in Italian). Etimologia. Retrieved January 2011. {{cite web}}: Check date values in: |accessdate= (help)
  17. ^ "Lefthanded scissors explained". dailymotion.com (video).
  18. ^ "The First Left-Handed Piano".
  19. ^ "Southpaws: Doing It Right the Wrong Way". fightbeat.com. Retrieved August 2006. {{cite web}}: Check date values in: |accessdate= (help)
  20. ^ "Rules of Major League Baseball, Section 1.04" (PDF). MLB.com.
  21. ^ 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.
  22. ^ Morris, Evan (1995). "Word detective research". Retrieved June 2006. {{cite web}}: Check date values in: |accessdate= (help)
  23. ^ "Definition for "southpaw"". Oxford English Dictionary Online. {{cite web}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help); Missing or empty |url= (help)
  24. ^ a b "Finding Power Tools for Left Handed People". Great Home Improvements. Retrieved 14 Jan 2011.
  25. ^ "A question of the left being right - and normal". China Daily. February 22, 2008. Retrieved 01-19-2011. {{cite web}}: Check date values in: |accessdate= (help)
  26. ^ Right-Hand, Left-Hand official website Accessed June 2006.
  27. ^ "Sinister and Rich: The evidence that lefties earn more", by Joel Waldfogel. Appeared in Slate on August 16, 2006.
  28. ^ McManus, Chris (2004). Right Hand, Left Hand: The Origins of Asymmetry in Brains, Bodies, Atoms and Cultures. Harvard University Press. ISBN 978-0674016132.
  29. ^ Wright, Ed (2007). Left-handed History of the World. Barnes & Noble. ISBN 978-0760787045.
  30. ^ a b "A Vast Left-Handed Conspiracy". The Washington Post. 2008. Retrieved January 2011. {{cite web}}: Check date values in: |accessdate= (help)
  31. ^ "Another left-handed president? It's looking that way". Pittsburgh Post-Gazette. 2008. Retrieved January 2011. {{cite web}}: Check date values in: |accessdate= (help); Unknown parameter |month= ignored (help)
  32. ^ "Four Out of Five Recent Presidents Are Southpaws". ABC News. 2008. Retrieved January 2011. {{cite web}}: Check date values in: |accessdate= (help); Unknown parameter |month= ignored (help)
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