Left-handed

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A person who is left-handed primarily uses his or her left hand, more so than the right hand; a left-hander will probably use the left hand for tasks such as personal care, cooking, and so on. Writing is not as precise an indicator of handedness as it might seem, because many left-handed people write with their right hand but use their left hand for other tasks.

Contents 1 Demographics 2 Causes of left-handedness 3 Social stigma and repression of left-handedness 3.1 Common names for left-handedness 3.1.1 Southpaw 3.1.2 Ciotóg 3.2 Linguistic suggestion 3.3 Inaccessibility of implements and skills 3.4 Technical advantages 3.5 Cultural stigmatisation 3.6 Famous left-handed people 4 Left-handedness and intelligence 5 "Disappearing" left-handers 6 Left-handers in sports 7 Left-sidedness 7.1 Traffic flow 7.2 In humans 7.3 Possible effects in humans on thinking 7.4 In animals 8 See also 9 Sources 10 External links

[edit] Demographics

Approximately 8 to 15% of the adult population is left-handed.^[1] Studies indicate that left-handedness is more common in males than females.^[2] Left-handedness, in comparison to the general population, also appears to occur more frequently in identical twins,^[3],^[4] and several groups of neurologically disordered individuals (people suffering from epilepsy,^[5] Down's Syndrome,^[6] autism,^[7] mental retardation^[8], dyslexia, etc.) Statistically, the identical twin of a left-handed person has a 76% chance of being left-handed, identifying the cause(s) as partly genetic and partly environmental.^[9] Also people of South Asian, Eastern European, Southeast Asian descent are more left-handed than any other ethnic groups in the world^[10], while people of Western European, Northern European, and African descent are less left-handed.^[10]

[edit] Causes of left-handedness

See main article at handedness.

• Long-term impairment of the right hand: Studies show that people with long-term impairment of the right hand are more likely to become left-handed, even after their right hand heals. Such long term impairment may include from 6 months or more.
• Testosterone: According to one theory, exposure to higher rates of testosterone before birth can lead to a left-handed child.^{[citation needed]} 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.

  The male brain matures later than that of the female, and the left hemisphere matures later than the right.

  Testosterone suppresses the growth of the left hemisphere and so more neurons migrate to the right hemisphere. 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 auto-immune disorders, learning disorders, dyslexia, and stuttering, as well as increased spatial ability.
• Birth stress theory: Left-handedness may be due to stress at birth.^{[citation needed]}
• Ultrasound theory: A popular theory is that ultrasound scans may affect the brain of unborn children, causing higher rates of left-handedness in mothers who have ultrasound scans compared to those who do not. This is probably based on a few studies ^{[11] [12]}where this relation is studied. In one of these the authors claim that "...we found a possible association between routine ultrasonography in utero and subsequent non-right handedness among children in primary school." However later in the same article the authors state that "Thus the association ... may be due to chance" and "The result was not significant, suggesting that the study had insufficient statistical power to resolve the relationship between ultrasonography and subsequent left handedness in the child"
• Learn-and-apply theory: A child simply learns from its environment and, as a result, the majority of people learn to be right-handed; the same goes for left-handed people, and this explains why left-handedness appears to be genetic.^{[citation needed]}

• learned left-hander. This left-hander writes with the left hand but has relatively poor handwriting, and shows dual hemispheric activation during verbal processing. Because preverbal children are not lateralized for hand use, these left-handers may have initially chanced to successfully manipulate some toy with their left hand and continued to use their left hand for toy manipulation. When eventually given a pencil or crayon, because of past reinforcement, they employ their left hand, and continue to use their left hand when they write even when they may be naturally right-handed. This, of course, is quite inefficient neurologically, as described above, and because of the additional processing time required, may be the reason quite a few left-handers stutter when they are young and have notoriously poor handwriting.^{[citation needed]} It is believed that eventually these left-handers develop verbal processing function in their right hemisphere too, and that these individuals become the left-handers who naturally show dual hemispheric activation during verbal processing.

• natural or genetic left-hander. Such persons function normally but are more likely to process language (at least in part) in the right hemisphere.

• pathological left-hander. Left-handers comprise almost 20% of the mentally retarded population and 28% of the severely and profoundly mentally retarded population.^{[citation needed]} It is believed these individuals are both retarded and left-handed for the same reason: brain damage to their left hemisphere as a result of a prenatal or postnatal event. It is also possible that a nutritional insult results in left hemisphere aberration. If the verbal processing area in the left hemisphere is damaged early in life, even partially, the right hemisphere would assume verbal processing functions, along with other hemispheric functions. This would account for the left-handers who process verbal material in their right hemisphere and, depending upon the severity of the brain damage, would also account for the higher proportion of left-handers found in the retarded population. There is no genetic component to this type of left-handedness.

[edit] Social stigma and repression of left-handedness

[edit] Common names for left-handedness

There are many colloquial terms used to refer to a left-handed person. Some are just slang or jargon words, while others may be offensive either in context or in origin. In more technical contexts, 'sinistral' may be used in place of 'left-handed' and 'sinistrality' in place of 'left-handedness'. Both of these technical terms derive from sinister, a Latin word meaning 'left'^[13].

[edit] Southpaw

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.^[14] Ballparks are often designed so that the batter is facing east, in order that the afternoon or evening sun does not shine in his/her eyes. This means that left-handed pitchers are throwing from the south side. The first use of the term is credited to Finley Peter Dunne. However, the Oxford English Dictionary lists a non-baseball citation for "south paw", meaning a punch with the left hand, as early as 1848,^[15] just three years after the first organized baseball game.

In boxing, someone who boxes left-handed is frequently referred to as southpaw. The term is also used to refer to a stance in which the boxer places his right foot in front of his left, so it is possible for a right-handed boxer to box with a southpaw stance. Most boxers, southpaw or otherwise, tend to train with sparring partners who adopt a right-handed stance, which gives southpaws an advantage.

Jim Ross, a pro wrestling play-by-play commentator often uses the term. He has most often labeled left-handed wrestlers William Regal and Carlito as southpaws.

[edit] Ciotóg

Ciotóg is an Irish word used to describe left-handed people, which also means 'strange person'^[16].

[edit] Linguistic suggestion

Some left-handed people consider themselves oppressed, even to the point of prejudice. Etymology often lends weight to the argument:

In many European languages, "right" is not only a synonym for correctness, but also stands for authority and justice: German and Dutch, recht, French, droit, Spanish, derecho; in most Slavic languages the root prav is used in words carrying meanings of correctness or justice. Being right-handed has also historically been thought of as being skillful: the Latin word for right-handed is "dexter," as in dexterity; indeed, the Spanish term diestro means both "right-handed" and "skillful". In Irish, "deas" means "right side" and "nice". "Ciotóg" is the left hand and is related to "ciotach" meaning "awkward".

Meanwhile, the English word "sinister" comes from the Latin word "sinistra,-us,-um", which originally meant "left" but took on meanings of "evil" or "unlucky" by the Classical Latin era. Alternatively, "sinister" comes from the Latin word sinus meaning "pocket": a traditional Roman toga had only one pocket, located on the left side for the convenience of a right-handed wearer.^{[citation needed]} The contemporary Italian word sinistra has both meanings of sinister and left. The Spanish siniestra has both, too, although the 'left' meaning is less common and is usually expressed by 'izquierda,'^[17] a Basque word. The German word for left is links, and the adjective link in German has the meaning of "slyly" or "devious", while linken means "to betray" or "to cheat" (sb.).

A left-hander was supposed to be not only unlucky, but also awkward and clumsy, as shown in the French gauche, the German links and linkisch and the Dutch expression "twee linkerhanden hebben" ("to have two left hands", which means being clumsy). As these are all very old words, they support theories indicating that the predominance of right-handedness is an extremely old phenomenon. In Portuguese, the most common word for left-handed person, canhoto, was once used to identify the devil, and canhestro, a related word, means "clumsy".

In ancient China, the left has been the "bad" side. The adjective "left" (左 Mandarin: zuǒ) means "improper" or "out of accord." For instance, the phrase "left path" (左道 Mandarin: zuǒdao) stands for illegal or immoral means. In some parts of China, some adults can still remember suffering for the "crime" (with suitable traumatic punishments) of not learning to be right-handed in both primary and secondary schools, as well as in some "keeping-good-face" families.

In Norwegian, the expression venstrehåndsarbeid (left-hand work) means "something that is done in a sloppy or insatisfactory way".

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" and derives from the Latin root "sinister."^[18]

[edit] Inaccessibility of implements and skills

Left-handed people are placed at a constant disadvantage by society. Nearly all tools and devices are designed to be comfortably used with the right hand. For example, scissors, a very common tool, are arranged so that the line being cut along can be seen by a right-handed user, but is not visible to a left-handed user. Furthermore, the handles are often molded in a way that is very difficult for a left-hander to hold, and extensive use can lead to severe discomfort. Some computer mice are made to fit the right hand only. Rulers too can be difficult to use, being often designed in a manner that forces left-handers to measure items upside-down. While European-style kitchen knives are symmetrical, Japanese kitchen knives have the cutting edge ground asymmetrically, with ratios ranging from 70-30 for the average chef's knife, to 90-10 for professional sushi chef knives; left-handed models are rare, and must be specially ordered and custom made. ^[19]

The lack of left-handed tools and machines in many workplaces is not only a nuisance to many left-handers, but has actually placed them at peril. One prime example is the band saw, whose standard design is convenient for right-handers but requires left-handers to pass their arms dangerously close to the cutting blade with each and every pass of the saw. ^[20] Some factories have installed left-handed equipment only after successful class-action lawsuits on behalf of left-handed employees. ^[21]

Writing is difficult to learn for a left-handed child if, as is usually the case, the writing teacher refuses to teach left-handed children in a way that is easy for them. This is because, when properly done, left-handed writing is a mirror image to that of the right-hander, making the learning process confusing for the left-handed student. The result is that the majority of left-handed people write with their hand curled around the pen so that it can meet the paper at the same angle as the right hander, rather than simply tilt the paper the opposite way. Once this habit is formed, it is difficult to break. This curling of the hand results in the heel of the palm being placed behind the writing, forcing the writer to lift it off the paper and making the grip even more awkward. When the left hand is held correctly, it is below the writing, as is typical for right-handers.

Left-handed people in the Arab world and Israel actually have it easier, because writing in their languages runs right to left, preventing left-handers from running their hand on the ink as happens with left to right languages. Ironically, the left hand is considered unclean in the Islamic world and doing several tasks with one's left hand is discouraged (eating, etc), although not forbidden.

Many well-intentioned companies have manufactured products with left-handers in mind, but have still failed to meet left-handers' needs. For instance, many companies have produced "left-handed scissors" by simply inverting the scissors' handles, making the grip work for the left-hander. Unfortunately, for scissors to function in a truly left-handed manner, their blades must also be mirror-inverted, without which the left-hander is forced to make a "blind cut" because the blade obscures the paper from view. Fiskars is one company that has produced truly left-handed scissors, inverting both the blades and the handles.

[edit] Technical advantages

One, and perhaps the only, universally common technological implement actually favoring left-handers is the QWERTY keyboard layout. Since this layout contains far more of the common English letters on the left side of the keyboard, the left hand does a solid majority of the typing, giving left-handed typists an advantage.^[22]

[edit] Cultural stigmatisation

Until the latter part of the twentieth century, Roman Catholic nuns in United States elementary schools would punish children for using their left hand to write, typically by slapping their left hand with a ruler if they attempted to pick up a pen with it.^{[citation needed]} As late as the early 20th century, school teachers in the Netherlands would force right-handed writing (thus, ambidexterity) on left-handed writing children. An example of such treatment involves baseball players Lou Gehrig and Babe Ruth, who both hit and threw left-handed and wrote right-handed after enduring left-handed suppression during their formative years.^{[citation needed]}

Left-handedness was often interpreted as a sign of Satanic influence, and thus prohibited. Many examples can be found in the Christian-Greek scriptures in which the wicked or evil sit at the left hand of God, while the righteous sit at the right hand of God, during the Last Judgment. The Inuit also believed that every left-handed person was a sorcerer.^{[citation needed]}

The Romans also frowned upon left-handedness. A left-handed boy who was training to be in a Roman legion would have his hand bound to his side, and would be forced to use the gladius with his right hand. This was done out of necessity, as a left-handed Roman would have interfered with the cohesion of the Roman legions.

The use of left hand was also frowned upon in Asia. Allegedly, though there were few examples of its happening, a Japanese man could divorce his wife if he discovered that she was left-handed.^{[citation needed]}

Until very recently, in Chinese societies, left-handed people were strongly encouraged to switch to being right-handed. However, this may be in part because, while Latin characters are equally easy to write with either hand, it is more difficult to write legible Chinese characters with the left hand. The prescribed direction of writing each line of a Chinese character is designed for the movements of the right hand, and some shapes tend to feel awkward to follow with the left hand's fingers. It results in a less soft writing than it would be with the right hand.

In many parts of the world, such as Indonesia, it is considered impolite to eat and accept gifts with the left hand. The reason for this is that a person who uses his left hand to eat would often cause trouble with the person to the left of him. Another stated reason for this is that the left hand is used in some countries, like Indonesia, during a bathroom visit.^{[citation needed]}

A profound Arab stigma against left-handedness dates to a pre-industrial period when paper was extremely rare and (in desert regions) water was too precious to be used for hand-washing. Because it was necessary to use one hand for wiping oneself after defecation, and because it was impossible to cleanse this hand thoroughly, the hand used for this task (traditionally, the left hand) was deemed unfit to be used for any other activity, especially as most Arabs of that time lacked eating utensils, and so they ate with their fingers (of the right hand) from communal dishes, while keeping the left hand entirely concealed at mealtime. To this day, it is widely regarded as taboo in Arab culture to handle food with the left hand. Offering one's left hand for a handshake greeting, or even waving it in greeting without touching, would be considered a serious personal insult in Arab society. Left-handers are also persecuted to some degree in the Arab World due to this taboo.

[edit] Famous left-handed people

Main article: List of famous left-handed people

Despite the suppression, there have been many famous left-handed people, and the associated right brain hemisphere that is said to be more active in left-handed people has been found in some circumstances to be associated with genius and is correlated with artistic and visual skill.

Many members of the British royal family are left-handed. Genetic factors are generally used to explain this. King George VI (who was the younger brother of Edward VIII, and therefore not expected to inherit the throne) was left-handed. During his boyhood and adolescence, his father George V required the prince to wear a long string tied to his left wrist; whenever he used his left hand, his father would tug the string violently, hoping to train him to become right-handed. George VI's severe stammer may or may not have developed as a result of this. Grand Duchess Maria Nikolaevna of Russia, a great-granddaughter of Queen Victoria of the United Kingdom, always used her left hand when she was sketching. John Heard, star of the cult hit C.H.U.D. is left-handed. Nelson Rockefeller was also left-handed; his father used this same string technique in an equally unsuccessful attempt to switch him to right-handedness.

Seven Presidents of the United States were left handed (approx. 16%). They are: James Garfield; Herbert Hoover; Harry S. Truman; Gerald Ford; Ronald Reagan; George H. W. Bush; Bill Clinton. ^[23]

Many famous people throughout history were also left-handed: Albert Einstein; Leonardo da Vinci; Picasso; and Jack the Ripper.

Billy The Kid was thought to be left handed due to a mirrored image of him which suggested he kept his gun on his left hand side. Even after it was revealed to be a reversed image, some people refused to believe this to be true, and now either regard him to be either ambidextrous or left handed.

Although Jimi Hendrix could play a guitar right-handed, he would usually play a regular right-hand guitar upside-down. In doing so, he would string the guitar in reverse order, thereby placing the thinnest string closest to the floor as in regular guitar playing.

[edit] Left-handedness and intelligence

A common belief suggests that left-handed people are more intelligent or creative than right-handed people. While there is an unresolved debate within the scientific community on how to operationalize both intelligence and creativity, some studies have demonstrated a small positive correlation between left-handedness and creativity/intelligence.

In his book Right-Hand, Left-Hand,^[24] Chris McManus of University College London, argues that the proportion of left-handers is rising 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 widens their range of abilities, and the genes that determine left-handedness also govern development of the language centers of the brain.

In Britain, a study in the 1970s found that around 11% of men and women aged 15-24 were left-handed, compared to just 3% in the 55-64 age category.^[25] McManus suggests a number of factors that may be driving this increase:

• Left-handers were severely discriminated against during the 18th and 19th centuries and it was often "beaten out" of people
• In adulthood, left-handers were often shunned by society, resulting in fewer marrying and reproducing
• As discrimination declined in the 20th century, the number of natural left-handers who stayed left-handed increased
• The rising age of motherhood contributed as, statistically, older mothers are more likely to give birth to left-handed children. In fact, it has been found that women over the age of forty have 128% more chance of having a child that will be left-handed than a woman in her 20s.^{[citation needed]}

McManus says that the increase could produce a corresponding intellectual advance and a leap in the number of mathematical, sporting, or artistic geniuses.

Unfortunately, they tend to be over-represented at both ends of the intellectual scale, and as well as geniuses, the group also produces a disproportionately high number of those with learning handicaps. There have been suggestions of links between left-handedness and dyslexia, stuttering, and child autism, among other disabilities.^{[citation needed]}

In 2006, researchers at Lafayette College and Johns Hopkins University in a study found that left-handed men are 15% richer than right-handed men for those who attended college, and 26% richer if they graduated. The wage difference is still unexplainable and does not appear to apply to women.^[26]

As well as possible intelligence advantages, being left-handed can also bring about other benefits, including:

• Brain hemisphere division of labor: The premise of this theory is that since both speaking and handiwork require fine motor skills, having one hemisphere of the brain do both would be more efficient than having it divided up.^{[citation needed]}
• Advantage in hand-to-hand combat: Left-handers have a 'surprise' factor in combat, since the majority of the population is right-handed.

[edit] "Disappearing" left-handers

Statistics show that older people are less likely to be left-handed than their younger counterparts — the percentages of left-handed people sharply drop off with increased age. In America, 12% of 20 year olds are left-handed, while only 5% of 50 year olds and less than 1% of people over 80 are.

A study^[27] (no longer deemed credible) published in 1991 claimed that these statistics indicate that left-handed peoples' lifespans are shorter than those of their right-handed counterparts by as much as 9 years. The authors explained this gap by asserting that left-handed people are more likely to die in accidents as a result of their "affliction," which renders them clumsier and ill-equipped to survive in a right-handed world.

Researchers have attributed most of the difference between the age groups to the fact that it was common in earlier times for schools to force all students to write, use cutlery and play sports right-handed. Older people who are naturally left-handed would be more likely to have experienced this.^{[citation needed]} However, this reasoning may not account for all the difference, and a full explanation for the "disappearing southpaws" remains elusive.

It has also been suggested that the percentage of children born left-handed may have been increasing over time.

[edit] Left-handers in sports

Being left-handed can be an advantage in many one-on-one or face-to-face sports. For example, in fencing, a right-handed fencer is generally more accustomed to facing another right-handed fencer, simply because being right-handed is more common. A left-handed fencer is generally more accustomed to facing a right-handed opponent for the same reason. Therefore, when a right-handed fencer faces a left-handed opponent, this difference in past experience grants a slight yet noticeable advantage to the left-handed combatant. The same advantage may be present for most one-on-one or face-to-face sporting events.

In tennis, left-handers impart spin on the ball that is opposite of that which a right hander would hit. As a result, right-handed players (who are accustomed to playing right handers) have difficulty dealing with a left-hander's shots which curve in a direction opposite to what they are accustomed to facing. Also, a left handed players straight forehand shot will go to the left, or backhand, of the right handed player, a more difficult shot for most players, and thus easier for a left handed player to hit a winning shot.

Professional, heavyweight boxing appears to be something of an exception to the rule that being a southpaw confers an advantage. Until Karl Mildenberger fought Muhammad Ali in 1966, there had not been a southpaw challenger for the heavyweight title, and hence no southpaw champion, and there have only been two southpaw heavyweight title holders since then, Michael Moorer, who became the first southpaw to hold a heavyweight title, and Corrie Sanders. It is worth distinguishing between the southpaw stance and being left-handed, because some trainers will train a naturally left-handed boxer to fight in an orthodox stance, not merely for convenience but because there may be an advantage in having the jab delivered with the stronger hand. Hence a number of boxers who fought in an orthodox stance may have been converted left-handers.

Baseball is particularly suited to left-handed hitters for four reasons: left-handers are already a step or two closer to first base in their batter's box before they even hit the ball so are more likely to beat out close plays; after finishing a full swing, a left-handed hitter is facing first base, so that there is no need to pivot before running the baseline; many baseball parks have shorter right field fences which gives left-handed sluggers a few more home runs that would otherwise be outs; and finally, most pitchers are right-handed which gives the left-handed hitter a better angle to see the ball and causes curve and sliding pitches to move towards them, rather than away. That is why a good switch hitter is considered valuable. Also, it is generally preferred (but not required) that first-basemen be left-handed to give them a better tagging angle on pick-off moves. Left-handed fielders cannot play third base, shortstop, or second base, however, because the throwing position towards first base is awkward for a lefty. Catchers are usually right-handed as well, because it is difficult to throw to third base in an attempt to catch a base-stealer if you are left-handed. A left-handed pitcher naturally faces toward first base, and thus can easily keep an eye on a runner trying to steal second. However, a right-handed pitcher has a more natural body movement in throwing the ball towards first base, when attempting to pick off the runner.

In football (soccer), left-handed players are often more skilled at playing with the left foot (though being left-handed does not necessarily result in being left-footed), which makes them valuable as they can play better on the left side of the field than right-handed players. Interestingly, in the sport of ice hockey, there are many more right-handed shooters. When shooting left, the player's left hand is in the middle of the stick, and the right hand is at the top of the stick. When skating fast, or stretching to reach a far away puck, a player will often use only the top hand on the stick. Many right-dominant players shoot left-handed, allowing them to use their dominant hand when wielding the stick one-handed. The majority of goaltenders also catch with their left hand.

In water polo, being left-handed allows a player to have an easier time shooting from the right side of the field, as having their shooting hand towards the middle of the field allows them to whip the ball around the keeper and into the upper left corner, a shot which a right-hander in the same position would find impossible. Also, when driving into the center from the right side, a left-handed player can take a dry pass and immediately shoot, whereas a right-handed player would require a wet pass and have to try and chip the goalie on a pop shot. This is why many teams like to have left-handed players, and why they tend to only play on the right (right-handed players have all similar advantages on the left side of the pool).

In Cricket, left-handed players have thrived over the years. Many technically sound batsmen have been left-handed. As of mid 2006, each and every of the Test playing nations have at least one left-handed batsman in their side. One of the reasons for this is that having a mix of right and left-handers tends to disrupt the bowler's accuracy, because when both a right-handed batsman and a left-handed batsman are batting, the bowler must adjust the line he is bowling when the batsman change ends. Some famous left-handed cricketers include yesteryear greats like Graeme Pollock, Allan Border, Gary Sobers, Wasim Akram and Mike Whitney; and contemporary greats Brian Lara, Sourav Ganguly, Sanath Jayasuriya, Adam Gilchrist, Graeme Smith, Mike Hussey and Matthew Hayden. It is also well-known that Sachin Tendulkar writes left-handed.

Minor sports where left-handedness is a significant advantage include Eton Fives, where the buttress is on the left, the idea serve placing the ball at the bottom corner - almost impossible for a right-handed player to reach. Another is Real (Royal) Tennis, in which the serve along the penthouse is far easier with the left hand than with the right.

In some sports, the rules, equipment or a combination of the two, confer a disadvantage to left-handed players. For example, a written rule in polo states that one must not hold a stick in his or her left hand.^[28] There are very few left-handed professionals in polo; all are required to use their right hand.^{[citation needed]} Jai alai is another sport where left-handed play is forbidden.

Provisions against left-handedness in field hockey are less direct, but still effectively require right-handed play. One rule states that the ball cannot be played with the back of the stick^[29] while another specifies that the stick be flat on its left side,^[30]. The left side of the stick is the "natural" side for a right-handed player. When playing with the stick in one hand (playing reverse), this can give an advantage back to the left-handers. Having all players play with the same handedness is essential to keeping hockey a non-contact sport: a left-hander and a right-hander competing for the ball would tend to collide. All-left-hander matches are possible, but rare.

The vast majority of firearms are designed for right-handed shooters, with the operating handle and safety set up for manipulation by the right hand, and fired cartridge cases ejected to the right. A left-handed shooter must either purchase a left-handed 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 them or shell cases being ejected towards their body), or learn to shoot right-handed (which may pose additional problems, primarily that of ocular dominance.)

[edit] Left-sidedness

[edit] Traffic flow

It is argued that Napoleon's left-handedness contributed to traffic flowing on the right side of the road in post-revolutionary France. The reasoning behind this evolution stems from Napoleon having to fight in wars with his sword in his left hand and that he reportedly converted his army to fight the same way. This would have entailed the French cavalry of the day to approach opponents from their right.

[edit] In humans

Studies show that left-handedness does not necessarily correspond with "left-sidedness." (Using your left foot to kick with, for example.) The same thing holds with "eyedness." It has also been found that people have dominant sides of the body, such as the eye, foot, and ear.

[edit] Possible effects in humans on thinking

There are many theories on how being left-handed affects the way a person thinks. One theory divides left- and right-handed thinkers into two camps: visual simultaneous vs. linear sequential.^{[31][32][33][34]}

According to this theory, right-handed people are thought to process information using a "linear sequential" method in which one thread must complete its processing before the next thread can be started.

Left-handed persons are thought to process information using a "visual simultaneous" method in which several threads can be processed simultaneously. Another way to view this is such: Suppose there were a thousand pieces of popcorn and one of them was colored pink. The right-handed person — using the linear sequential processing style — would look at the popcorn one at a time until they encountered the pink one. The left-handed person would spread out the pieces of popcorn and visually look at all of them to find the one that was pink. A side effect of these differing styles of processing is that right handed persons need to complete one task before they can start the next. Left-handed people, by contrast, are capable and comfortable switching between tasks. This seems to suggest that left-handed people have an excellent ability to multi-task, and anecdotal evidence suggests that there are more creative stems due to this ability to multi-task.

Right-handed people process information using "analysis", which is the method of solving a problem by breaking it down to its pieces and analyzing the pieces one at a time. By contrast, left-handed people process information using "synthesis", which is the method of solving a problem by looking at the whole and trying to use pattern-matching to solve the problem. ^[35]

The hypothesis that left-handed people are predisposed to visual-based thought has been validated by a variety of evidence. In the 2004 book Brains that work a little bit differently^[36], researchers Allen D. Bragdon and David Gamon, Ph.D., briefly described some of the current research on handedness and its significance. "Handedness researchers Coren and Clare Porac have shown that left-handed university students are more likely to major in visually-based, as opposed to language-based subjects. Another sample of 103 art students found an astounding 47 percent were left- or mixed-handed." [page 76]

Ultimately, being left-handed is not an all-or-nothing situation. The processing styles operate on a continuum where some people are more visual-simultaneous and others are more linear-sequential.

This can be further explained in the use of computers. A computer processor can only process one piece of information at a time, regardless of how many tasks you may be running. But a computer with (for example) four processors; each processor still only processing one piece of information each but four pieces at once making the processing of information faster. In this sense, a right handed person can only process one piece of information at a time and would, in theory, think more slowly than a left-hander who can process (for example) four pieces of information at a time. Also, it is very difficult to ascertain the way a human being behaves within the black box that is the brain. Whether this theory about processing styles is valid or not will be borne out by future experimentation.

[edit] In animals

Most primates also exhibit a preference for using one hand over the other although their populations are not necessarily right-hand preferential.

The received wisdom among Inupiaq Eskimos is that most polar bears are left-handed^[37].

[edit] See also

• Right-handed
• Handedness
• Chirality (chemistry)
• Chirality (mathematics)
• Chirality (physics)
• List of famous left-handed people
• The Tale of Cross-eyed Lefty from Tula and the Steel Flea
• Geschwind-Galaburda Hypothesis
• Situs inversus
• Handedness and sexual orientation

[edit] Sources

[edit] 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
• Quirks & Quarks June 10, 2006 (CBC radio documentary on left-handedness including interviews with four scientists holding different views on the determinants of handedness)
• A left-handed senior citizen recalls the emotional torment he faced at a New York public school in the 1920's. (Audio slideshow)
• Anything Left-Handed Left-handed products and left-handed people.
• Famous Left-Handers
• Left-Handers Day - the official left-handers club site.
• There is an Association of left handers in India since 1992. Visit website http://www.lefthanders.org/
• Schwartz, Alyssa (2005). "Lefties face increased breast cancer risk," C-Health News, 30 September.
• Scans may 'cause brain changes', BBC News.
• Left-Handed Toons - left-handed cartoons by right-handed people
• prolevaky.cz - left handed resources in Czech and slovak language

Hand dexterity
Left-handedness – Cross-dominance – Right-handedness