A left-handed individual is colloquially referred to as a "leftie." 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.'yourDictionary Word of the Day: sinistral. Accessed June 2006. This may in turn originate from the Latin word for 'pocket,' sinus; the pocket in a Roman toga was on the left side, for the convenience of a right-handed wearer.

Demographics

Statistically, the twin of a left-handed person has a 76% chance of being left-handed. Ask Yahoo!: Why am I right-handed, but my brother is left-handed? Accessed June 2006.

Causes of left-handedness

No one knows for certain why the human population is right-handed-dominant, but a number of theories have been proposed.

Evolutionary theories

The warrior and his shield

There are a number of objections to this theory:

1. The heart is not that far off centre. Protecting it with a shield would result in a weak selective pressure.
2. There have not been enough generations since the Bronze Age to make a difference.
3. Analysis of ancient cave paintings indicates that humanity was dominantly right-handed long before the Bronze Age.Whitehouse, David (2004). "Left-handedness common in Ice Age," BBC News, 13 February.
4. Some believe it predicts that more men would be right-handed than women. However, data indicates that more males are left-handed than females. This objection also demonstrates a misunderstanding of heredity. The theory would predict that fewer left-handed males would survive but says absolutely nothing about ratios of male: female left-handedness after that time. Nor does it explain why there would be either right-or left-handedness to begin with.

Advantage in fist-fighting

A 2004 study by Charlotte Fauriet and Michel Raymond of the University of Montpellier II in France, published in the Proceedings of the Royal Society, argues that there is such a link. To prove their theory, Faurie and Raymond surveyed nine primitive societies in five separate continents. Through a mix of direct observation and existing data, they estimated the number of left-handed people within each population. They also looked at murder rates, thinking that those communities with higher murder rates might favor populations with more left-handed people. The more violence, the more chances lefties would have at issuing their unexpected left hook, or other such weapon, and come out on top.

Among these samples, they found strong support for the idea that, at least in primitive societies with higher levels of violence, lefties thrive. Onion, Amanda (2005). "The Left-Handed Advantage," ABC News, 17 February.

Like the previous theory, it too does not actually explain why handedness would arise in the first place. And moreover, its result has nothing to do with why right-handedness is more common.

Brain hemisphere division of labour

Objections:

1. It does not explain why the left hemisphere would always be the one controlling language. Why not 50% of the population left and 50% right?
2. While 95% of right-handers do indeed use the left side of the brain for speaking, it is more variable for left-handers. Some do use the right for linguistic skills, some use the left hemisphere, and others use both.

On the balance, it appears that this theory could well explain some left-handedness, but it has too many gaps to explain all left-handedness.

Several brain-scan studies have verified a fundamental difference between left-handed and right-handed brains. A right-handed person's brain is typically highly specialized, with a specific portion of the brain dedicated to each task. This same specialization is much less prevalent in left-handed brains. Left-handed stroke victims often rehabilitate more quickly than right-handed stroke victims, as the left-handed brain has a lesser tendency to compartmentalize and specialize its abilities.

Is left-handedness genetic?

Apparently, the Clan Kerr of Scotland built their castles with counter-clockwise staircases, so that a left-handed swordsman would be better able to defend it. However, a 1993 study found no statistically significant increase in left-handedness among people with the family name Kerr or Carr.

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. As a result of this mistreatment, George VI developed a severe stammer. Nelson Rockefeller was also left-handed; his father used this same string technique in an equally unsuccessful attempt to switch him to right-handedness.

There is a profound stigma against left-handedness in Arabian cultures. This stigma dates back many centuries, to the 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) while keeping the left hand entirely concealed at mealtime. To expose the left hand during a public meal is still considered profoundly offensive in many Arab cultures, especially in desert regions.

Biological theories

There is strong evidence that prenatal testosterone contributes to brain organization. One theory is that high levels of prenatal testosterone results in a higher incidence of left-handedness. See Geschwind-Galaburda Hypothesis.

Environmental theories

Birth stress

Difficult or stressful births happen far more commonly among babies who grow up to be left-handed or ambidextrous. Birth stress is also associated with a number of birth defects and complications, including cerebral palsy and autism.

There are objections to the birth stress theory:

1. Throughout history and throughout the world, the level of medicine and technology to assist with childbirth has improved. In spite of that, the proportion of left-handed people has not decreased.
2. It does not explain why humans are right-handed by default, with only birth stress making them left-handed. It could, however, explain left-handedness in combination with some of the other theories presented here.

Ultrasound

Social stigma and repression of left-handedness

Linguistic suggestion

In many European languages, "right" stands for authority and justice: German and Dutch, "recht", French, "droit" (from Latin 'directus'Appendix I: Indo-European Roots. The American Heritage Dictionary of the English Language: Fourth Edition, 2000.); in most Slavic languages the root "prav" is used in words "right", "correct", "justice" etc. Being right-handed has also historically been thought of as being skillful: the Latin word for right-handed is "dexter," as in dexterity; the Spanish "derecha" (also from Latin 'directus'Etimología de derecho, deChile.com. Accessed June 2006. (Spanish)) also means right.

On the other hand, the English word "sinister" comes from Latin and it originally meant "left" but took on meanings of 'evil, unlucky' by the Classical Latin era. "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. The modern-Italian "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,'Etimología de izquierda, deChile.com. Accessed June 2006. (Spanish) a Basque word. A left-hander was supposed to be not only unlucky, but also awkward and clumsy, as shown in the French "gauche" and the German "links" and "linkisch." 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: zuo) means "improper," "out of accord." For instance, the phrase "left path" (左道 mandarin: zuodao) 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 Norway, 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 at both sides." However, since it keeps the Latin root "dext," which means "right," it ends up conveying the idea of being "right-handed at both sides."

Daily suppression

In many parts of the world, such as Indonesia, it is considered impolite to eat and accept gifts with the left hand. The reason to this is 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. Until the latter part of the twentieth century, Roman Catholic nuns in American elementary schools (and possibly elsewhere, for example Dutch and German primary 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. 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.

Left-handedness was often interpreted as a sign of Satanic influence, and thus prohibited. The Inuit also believed that every left-handed person was a sorcerer.

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 interferred 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 once divorce his wife if he discovered that she was left-handed.

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.

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. As visual thinking is much promoted nowadays, left-handers cannot help but begin to gain more and more respect. As well, in certain fields, left-handedness is advantageous; for example, in baseball, where right-handed pitchers greatly outnumber lefties, it is commonly known that a left-handed batter is more successful against right-handed pitchers than a right-handed batter. In soccer, left-handed players are often more skilled at playing with the left foot (though being left-handed doesn't necessarily imply 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 left-handed shooters, and the majority of goaltenders catch with their left hand (forcing many of them to shoot left-handed, as well).

Common names for left-handedness

Southpaw

The generally accepted origins of the term is from baseball. Ballparks are often designed so that the batter is facing east to avoid the afternoon or evening sun shining in his eyes. This means that left-handed pitchers are throwing from the south side. The first usage 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,Morris, Evan (1995). Word detective research. Accessed June 2006. just three years after the first organized baseball game.

In boxing a left handed boxer is usually referred to as southpaw. They are often considered a more tricky opponent than the more common right-hander. The term is also used to refer to a stance in which the boxer places his right foot in front of his left.

Ciotog

Ciotog is an Irish-language word used to describe left-handed people which also means 'Strange Person.' "My Left Foot," The Kingdom, 24 July, 2003. Accessed June 2006. In Rocky I, Rocky says that the term "southpaw" came from a boxer named Paul whos left arm always faced to south Jersey.

Left-handedness and intelligence

In his book Right-Hand, Left-Hand,Right-Hand, Left-hand official website. Accessed June 2006. 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 centres of the brain.

In Britain, around 11% of men and women aged 15-24 are now left-handed, compared to just 3% in the 55-64 age category. Steele, James & Mays, Simon (c1995). New findings on the frequency of left- and right-handedness in mediaeval Britain. 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 was reduced 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

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.

"Disappearing" left-handers

A study (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. They 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 now attribute most of the difference between the age groups to the fact that older people would be more likely to have experienced pressure to switch hands, a factor not affecting the younger generations. This is supported by the fact that more women than men switched hands, and women live longer than men. However, this reasoning cannot explain all variation, and "the case of the disappearing southpaws" remains a mystery.

Another theory is that some lefties switch hands later in life, due to conformist pressures, or a "biological imperative." It has also been suggested that the percentage of children born left-handed may have been increasing over time.

Left-handers in sport

Being left-handed can be an advantage in many sports. For example, in fencing, a right-handed fencer is more accustomed to facing another right-handed fencer simply because being right-handed is more common. A left-handed fencer is also more accustomed to facing a right-handed opponent for the same reasons. Therefore, when a right-handed fencer faces a left-handed opponent, the righty is not as used to fighting a lefty as the lefty is used to fighting a righty, causing a slight yet noticable advantage. The same advantage may be present for most one-on-one or face-to-face sporting events.

Left-sidedness

In humans

In animals

See also

• Handedness
• List of famous left-handed people
• List of fictional left-handed characters
• The Tale of Cross-eyed Lefty from Tula and the Steel Flea
• Geschwind-Galaburda cluster
• Situs inversus

Sources

External links

• Lefties Have The Advantage In Adversarial Situations, ScienceDaily, April 14, 2006.
• Science Creative Quarterly's overview of some of the genetic underpinnings of left-handedness
• Quirks & Quarks June 10, 2006 (CBC radio documentary on left-handedness including interviews with four scientists holding different views on the determinants of handedness)

Motor skills

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