Handedness is an individual’s preferential use of one hand, known as the dominant hand, due to it being stronger, faster or more dextrous.
The other hand is comparatively often the weaker, less dextrous or simply less subjectively preferred, is called the non-dominant hand.
In a study of children in US grades 1–6, left handers comprised 9.6% of the sample, with 10.5% of male children and 8.7% of female children being left-handed.
Around 90% of people are right-handed.
Handedness is often defined by one’s writing hand.
It is fairly common for people to prefer to do a particular task with a particular hand.
People with true ambidexterity with equal preference of either hand, are rare.
in some cultures, the use of the left hand can be considered disrespectful.
Most of the current research suggests that left-handedness has an epigenetic marker—a combination of genetics, biology and the environment.
Because the vast majority of the population is right-handed, many devices are designed for use by right-handed people, making their use by left-handed people more difficult.
Left-handed people have an advantage in sports that involve aiming at a target in an area of an opponent’s control, as their opponents are more accustomed to the right-handed majority.
Left-handed people are over-represented in baseball, tennis, fencing, cricket, boxing, and mixed martial arts.
Ambidexterity refers to having equal ability in both hands, but those who learn it still tend to favor their originally dominant hand.
This is uncommon, with about a 1% prevalence.
Mixed-handedness or cross-dominance is the change of hand preference between different tasks.
Mixed-handedness or cross-dominance is about as widespread as left-handedness.
Mixed-handedness or cross-dominance is highly associated with the person’s childhood brain development.
Handedness may be measured behaviourally by performance measures or through questionnaires as preference measures.
Handedness displays a complex inheritance pattern.
If both parents of a child are left-handed, there is a 26% chance of that child being left-handed.
A study of twins from 25,732 families indicates that the heritability of handedness is roughly 24%.
It is conclude that handedness is polygenic and estimate that at least 40 loci contribute to the trait.
Genes involved in the determination of left-right asymmetry in the body play a key role in handedness.
The same mechanisms that determine left-right asymmetry in the body also play a role in the development of brain asymmetry as handedness being a reflection of brain asymmetry for motor function).
Studies have indicated that individuals who have had in-utero exposure to diethylstilbestrol, a synthetic estrogen, used between 1940 and 1971 were more likely to be left-handed over the clinical control group.
Diethylstilbestrol animal studies suggest that estrogen affects the developing brain, including the part that governs sexual behavior and right and left dominant.
There may be a weak association between ultrasound screening (sonography used to check the healthy development of the fetus and mother) and left-handedness.
Twin studies indicate that genetic factors explain 25% of the variance in handedness, and environmental factors the remaining 75%.
A handedness theory is the brain hemisphere division of labor, and most people may use the non-speaking (right) hemisphere for perception and gross motor skills, and most people, the left side of the brain controls speaking.
The specialized fine motor areas controlling speech are most efficiently used to also control fine motor movement in the dominant hand.
As the right hand is controlled by the left hemisphere and the left hand is controlled by the right hemisphere most people are, therefore right-handed.
The majority of left-handers have been found to have left-hemisphere language dominance—just like right-handers.
Only around 30% of left-handers are not left-hemisphere dominant for language.
Handedness in the womb is a very accurate predictor of handedness after birth :39% of infants (6 to 14 months) and 97% of toddlers (18 to 24 months) demonstrated a hand preference.
Infants have been observed to fluctuate heavily when choosing a hand to lead in grasping and object manipulation tasks, especially in one- versus two-handed grasping.
Right-handed preference increases with age up to the teenage years.
Chris McManus of University College London argues that the proportion of left-handers is increasing: above-average quota of high achievers have been left-handed, and it is argued left-handers’ brains are structured in a way that increases their range of abilities.
Studies reveal that left-handed people differ from right-handers by only one IQ point.
Left-handers’ brains are structured in ways that can allow them to process language, spatial relations and emotions in more diverse and potentially creative ways.
A slightly larger number of left-handers than right-handers are especially gifted in music and math.
A study of musicians in professional orchestras found a significantly greater proportion of talented left-handers.
Studies of adolescents who took tests to assess mathematical giftedness found many more left-handers in the population.
Left-handers are overrepresented among those with lower cognitive skills and mental impairments, with those with intellectual disability being roughly twice as likely to be left-handed, as well as generally lower cognitive and non-cognitive abilities amongst left-handed children.
Left-handers are nevertheless also overrepresented in high IQ societies, such as Mensa:approximately 20% of the members of Mensa are lefthanded, double the proportion in most general populations.
A study found that left-handers were significantly more likely to perform better on intelligence tests than right-handers and that right-handers also took more time to complete the tests.
In a systematic review and meta-analysis, (Ntolka & Papadatou-Pastou) ( found that right-handers had higher IQ scores, but that difference was negligible (about 1.5 points).
Nelson, Campbell, and Michel discovered that when a child developed a consistent use of their right or left hand during infancy (such as using the right hand to put the pacifier back in, or grasping random objects with the left hand), they were more likely to have superior language skills as a toddler.
Children who became lateral later than infancy,when they were toddlers, showed normal development of language and had typical language scores.
Left-handers, particularly those with mixed-hand preference, performed significantly better than right-handers in musical memory tasks.
Studies have found a positive correlation between left-handedness and several specific physical and mental disorders and health problems, including:
Lower-birth-weight and complications at birth are positively correlated with left-handedness.
A variety of neuropsychiatric and developmental disorders like autism spectrum, bipolar disorder, anxiety disorders, schizophrenia, and alcoholism have been associated with left- and mixed-handedness.
A study showed that nearly 40% of children with cerebral palsy were left-handed, while another study demonstrated that left-handedness was associated with a 62% increased risk of Parkinson’s disease in women, but not in men.
Another study suggests that the risk of developing multiple sclerosis increases for left-handed women.
Left-handed women may have a higher risk of breast cancer than right-handed women and the effect is greater in post-menopausal women.
At least one study showed left-handers are more likely to suffer from heart disease, and are more likely to have reduced longevity from cardiovascular causes.
Left-handers may be more likely to suffer bone fractures.
Left-handers have a lower prevalence of arthritis and ulcer.
On average, left-handers have been found to have an advantage in fighting and competitive, interactive sports, which could have increased their reproductive success in ancestral populations.
There was no statistically 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.
Joshua Goodman found that left-handed people earn 10 to 12 percent less over the course of their lives than right-handed people, attributed this disparity to higher rates of emotional and behavioral problems in left-handed people.
Smaller physical distance between participants in sports increases the overrepresentation.
In fencing, about half the participants are left-handed.
In tennis, 40% of the seeded players are left-handed.
The term southpaw is sometimes used to refer to a left-handed individual, especially in baseball and boxing.
Some studies suggest that right handed male athletes tend to be statistically taller and heavier than left handed ones.
In cricket, the overall advantage of a bowler’s left-handedness exceeds that resulting from experience alone.
Only 10% of the general population is left-handed, the proportion of left-handed MLB players is closer to 39% of hitters and 28% of pitchers.
Historical batting averages show that left-handed batters have a slight advantage over right-handed batters when facing right-handed pitchers.
Because there are fewer left-handed pitchers than right-handed pitchers, left-handed batters have more opportunities to face right-handed pitchers than their right-handed counterparts have against left-handed pitchers.
Fifteen of the top twenty career batting average leaders in Major League Baseball history have been posted by left-handed batters.
Left-handed batters have a slightly shorter run from the batter’s box to first base than right-handers.
Defensively in baseball, left-handedness is considered an advantage for first basemen because they are better suited to fielding balls hit in the gap between first and second base, and because they do not have to pivot their body around before throwing the ball to another infielder.
Left handers have advantages and other sports including four wall handball, water polo, ice hockey, American football, and bowling
According to a meta-analysis of 144 studies, the best estimate for the male to female odds ratio was 1.23, indicating that men are 23% more likely to be left-handed.
A study found that people assigned male at birth whose gender identity did not align with their assigned sex, were more than twice as likely to be left-handed than a clinical control group (19.5% vs. 8.3%, respectively).
Paraphilias (atypical sexual interests) have also been linked to higher rates of left-handedness.
Greater rates of left-handedness have also been documented among pedophiles.
Non-sexual men and women were 2.4 and 2.5 times, respectively, more likely to be left-handed than their heterosexual counterparts.
Left-handed men were almost twice as likely to die in war as their right-handed contemporaries: because weapons and other equipment was designed for the right-handed.
Left-handed US sailors were 34% more likely to have a serious accident than their right-handed counterparts.
A high level of handedness (whether strongly favoring right or left) is associated with poorer episodic memory, and with poorer communication between brain hemispheres, which may give poorer emotional processing.
A high level of handedness is associated with a smaller corpus callosum whereas low handedness with a larger one.
Left-handedness is associated with better divergent thinking.
Writing from left to right as in many languages, in particular, with the left hand covers and tends to smear (depending upon ink drying) what was just written.
Aside from inconvenience, left-handed people have historically been considered unlucky or even malicious for their difference by the right-handed majority.
In many languages, the word for the direction “right” also means “correct” or “proper”.
Historically, being left-handed was considered negative, or evil.
The Latin adjective sinister means “left” as well as “unlucky”.
Negative connotations associated with the phrase “left-handed”: clumsy, awkward, unlucky, insincere, sinister, malicious, and so on.
Conversely, right-to-left alphabets, such as the Arabic and Hebrew, are generally considered easier to write with the left hand.
Kangaroos and other macropod marsupials show a left-hand preference for everyday tasks in the wild.
Studies of dogs, horses, and domestic cats have shown that females of those species tend to be right-handed, while males tend to be left-handed.