Left-handedness occurs in about 8% of the human population. It runs in families and an adoption study suggests a genetic rather than an environmental origin; however, monozygotic twins show substantial discordance.
Hand preference probably arises as part of the developmental process that differentiates the right and left sides of the body (called right-left asymmetry). More specifically, handedness appears to be related to differences between the right and left halves (hemispheres ) of the brain.
If the father is left-handed, the odds are 2 in 10. If the mother is left-handed, the odds rise to 3 in 10. And if both parents are left-handed, the child has a 4 in 10 chance of being left-handed. If a classic dominant-recessive model were in play, then left-handed people would only have left handed kids.
Special or not, lefties are born, not made: Genetics are at least partially responsible for handedness. Up until last year, it was assumed that hand preference comes from asymmetrical genes in the brain—two hands, two brain hemispheres, one is dominant.
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.
On the flip side, lefties have some disadvantages too.
Some studies show that left-handed people showed an imbalance in processing emotions with their left and right hemispheres of their brain. Left-handed people have a higher risk of brain disorders like schizophrenia, dyslexia or hyperactivity disorders.
Eleven percent of the population is born left-handed, and if they seem different, it's because they are! Learn six tips for raising a left-handed child.
About 10 percent of the population is left-handed. The rest are right-handed, and there are also about 1 percent who are ambidextrous, which means they have no dominant hand. Not only are lefties outnumbered about 9 to 1 by righties, there are health risks that appear to be greater for left handers, too.
Sometimes people who are left-handed are called “Southpaws”.
“Most left-handers seem to have similar language processing to right-handers,” Grimshaw says. For other one-sided brain functions, such as attention, emotion, music, and face perception, she says, there are less data. “But for the most part, left-handers do not differ obviously from right-handers.
Becoming proficient with your left hand will not happen overnight - it's a process that could take months or even years to complete. So if you want to learn how to use your left hand, you will need to commit to practicing daily. Set some time aside each day to practice your left handwriting.
In their analysis of 144 handedness and brain laterality studies—accounting for a total of nearly 1.8 million individuals—University of Oxford psychologists Marietta Papadatou-Pastou, PhD, and Maryanne Martin, PhD, found that males are about 2 percent more likely to be left-handed than females.
Left-handedness and longevity
In addition, some diseases associated with left-handedness are relatively rare and there is no evidence that left-handedness is associated with increased risk of common diseases such as malignancy, cerebrovascular and cardiovascular diseases.
Left-handedness is now accepted as a completely normal aspect of a child's development. A child's handedness will be fixed before they're born and won't be immediately apparent when they are an infant. Experts believe that if both parents are left-handed there is a 50-50 chance that a child will be left-handed too.
Results: Left-handed students had a probability of suffering from ADHD 2.88 greater than right-handers. ANOVAs on standardized scores indicated that the ADHD students exhibited higher number of errors and higher variability of reaction times as compared to the controls.
The results show evidence of a trend towards elevated levels of atypical handedness when it comes to differences in left- and mixed-handedness (p = 0.09 and p = 0.07, respectively), but do show clear evidence of elevated levels of non-right-handedness between individuals with ADHD and controls (p = 0.02).
Researchers have not yet found a genetic link between dyslexia and handedness and individuals with dyslexia, a learning difficulty that impacts on reading, writing and spelling abilities, are split 50:50 between right and lefthandedness.
McManus which found that the Netherlands has one of the world's highest prevalences of left-handedness at 13.23 percent. The United States isn't far behind with a rate of 13.1 percent while neighboring Canada has 12.8 percent. Elsewhere, rates of left-handedness are far lower and China is a good example.
Lefties can also use their status strategically in sports. They have an advantage in tennis, baseball and boxing, for example, because righties have a tough time predicting their less familiar moves. Lefties also have their own special day on the calendar.
The "highest risk" group is said to be those who are first born to older mothers (aged 30 or over) (Bakan et aI., 1973).
Lefties--or at least relatives of lefties--may be better than right-handed people at remembering events, according to a new study. Since the mid-1980s, scientists have known that the two brain hemispheres of left-handers are more strongly connected than those of right-handers.
A straightforward genetic link hasn't been proven, and it is possible for two right-handed parents to have a left-handed child. Theories include: Genes – perhaps genetic factors predispose a child to favour the right hand. A single gene might be passed from parents to children to influence which hand a child favours.
Sixty-four percent of the participating plastic surgeons were left handed (significantly higher than the approximate 12% of the general population; P = 0.007). Many of the left-handed doctors admitted to practicing musical instruments and various arts, crafts, and other hobbies.
Wright and Hardie (2012) found that left-handers reported higher levels of state anxiety but there was no difference in trait anxiety. They also demonstrated that when Trait Anxiety was controlled for, left-handers still showed a higher level of state anxiety compared to right-handers.