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A person who is left-handed primarily uses their left hand, more so than their 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 people who are left-handed write with their right hand and use their left for everything else.

People who are left-handed are technically said to be sinistral, and left-handedness is sometimes referred to as sinistrality. Both words derive from sinister, the Latin word for “left”. This word in turn derives from sinus, the Latin word for “pocket” referring to the fact that the pocket in a Roman toga was on the left side, for the convenience of a right-handed wearer.

Statistics of left-handedness

Approximately 10% of the population is left-handed. People who can use both hands equally well are ambidextrous. True ambidexterity is rare. See laterality.

Generally, there are about 10% more male left handers than female left handers (5.24% Male, 4.76% Female). Approximately one-third of identical twins are left-handed. Statistically, the twin of a left-handed person has a 76% chance of being left-handed.

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

This theory attempts to explain why left-handedness is rare by the position of a warrior's shield and his heart. Basically, since the heart is on the left side of the body, a right-handed warrior (who holds his shield with his left hand to free the right hand for a weapon) would be better able to protect his heart and therefore more likely to survive.

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.
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 variant of the above argument says that left-handed people have an advantage in fighting without weapons, because of the "surprise" factor. (This fact is well known to boxers and was employed to world-record effect on Nov. 4th 1947 when Mike Collins, a natural left-hander, emerged from his corner in a right-handed stance before suddenly shifting left and delivering the fight's first and last punch, knocking out opponent Pat Brownson in 4 seconds.)

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.

Like the previous theory, it too doesn't 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

This is the most commonly accepted theory of handedness. 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. And since in most people, the left side of the brain controls speaking, right-handedness would prevail. It also predicts that left-handed people would have a reversed brain division of labour. Lastly, since other primates do not have a spoken language (at least of the type we have) there would be no stimulus for right-handed preference among them, and that is true.

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?

Scientists previously believed handedness runs in families, but recent studies seem to run counter to what is increasingly looked upon as little more than unfounded lore. One study conducted in 1998 by researchers at James McDevitt University, Oklahoma, revealed that when both parents are left-handed, there is only a 26% chance of their child being left-handed (Only 10% of the human population are left-handed), an indication that genetics may not play the prominent role once thought in determining handedness. Thus, it is clear that genetics is not the only cause. Handedness must also be influenced by some of the other theories presented here.

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

Its basic premise is that left-handedness is due to brain damage during the birth process. Some statistics support this theory.

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

Scientists in Sweden say they have found evidence that ultrasound scans may cause brain changes in unborn babies, after they found men whose mothers had tests were more likely to be left-handed. The study suggested that scanning produced an extra three left-handed babies per one-hundred births. This research has come under some criticism, since it implies that left-handed people are in some way "brain damaged."

Social stigma and repression of left-handedness

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" stands for authority and justice: German and Dutch, "recht", French, "droit" (from Latin 'directus' ); 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') 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', 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.

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

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 molded in a way that is very difficult for a left hander to hold, and extensive use causes severe discomfort and pain. Computer mice are very frequently shaped to fit the right hand. Even writing is awkward, as the left hand is dragged over the text, resulting in smearing, and must be pushed to form writing as opposed to pulled using the right hand, especially in cursive writing. The hand must also be held at an extreme angle to prevent it from covering up what was just written, causing cramping. However, this difficulty is only present in cultures that write left to right.

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 Eskimos 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, it is commonly known that a left-handed batter is more successful against right-handed pitchers than a right-handed batter. A left-handed pitcher is more successful against left-handed batters than a right-handed pitcher. 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.

Common names for left-handedness

There are many colloquial terms by which a left-handed person can be referred. Some are just slang or jargon words, while others may be offensive either in context or in origin.

Southpaw

Southpaw is a term used to describe left-handed people, particularly within sports and in the United States.

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, 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.

The official mascot of the Chicago White Sox is named Southpaw due to the team's stadium location on the south side of the city.

Ciotog

Ciotog is an Irish language word used to describe left-handed people. It derives from the Irish word Ciotog which means 'Strange Person'.

Left-handedness and intelligence

A common belief suggests that left-handed people are more intelligent or creative than right-handed people, and this theory is supported by some evidence. Evidence such as numerous studies that prove left-handed children learn to come over obstacles at an earlier age, being left-handed in a primarily right-handed world.

In his book Right-Hand, Left-Hand, 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. 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

Statistics show that older people are less likely to be left-handed than their younger counterparts — the percentages of lefties 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. These numbers are surprisingly divergent — how can they be explained?

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.

Other contribution factors that have been suggested include that some lefties eventually succumb to conformist pressures, and that a "biological imperative" grips them late in life and they lose their left-handedness. Also, it has been suggested that the percentage of left-handed children born may have been increasing over time.

Left-handers in sport

There are many left-handers in sports; however, a written rule in Polo states that one must not hold a stick in their left hand. There are only three or four left-handed professionals in Polo, who are each required to use their right hand.

Left-handedness and developmental disorders

Studies have shown that left-handedness is more common in those suffering from pervasive developmental disorders (such as autism or mental retardation) than among the unaffected population.

Left-sidedness

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."

In animals

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

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

• Habib, Marlene (2000). http://www.canoe.ca/Health0007/06_hands.html
• http://www.sciencedaily.com/releases/2000/07/000710071931.htm
• http://news.bbc.co.uk/1/hi/health/1699905.stm
• Word detective research
• Chicago White Sox mascot Southpaw
• David Wolman's book explores the mystery and meaning of all things southpaw

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