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.
In fact, one of the more unusual hypotheses to explain the rarity of left-handedness is that a genetic mutation in our distant past caused the language centres of the human brain to shift to the left hemisphere, effectively causing right-handedness to dominate, Alasdair Wilkins explains for io9 back in 2011.
Handedness is most likely due to a combination of both genes and environment while some people have a greater chance of being left-handed if their parents are. You are more likely to become left-handed based on the presence of one or more genes, but you may need an environmental trigger for it to happen.
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.
If both parents were left-handed, the chance of their offspring also being left-handed was highest: 26 percent. This indicates that children of two left-handed parents have a higher chance of being left-handed, but also that three-quarters of them are still right-handed.
Babe Ruth. The Babe is probably the most famous left-handed slugger of all-time.
One potentially important determinant of a child's cognitive development is the preference for using the left or right hand. Left- or mixed-handedness has been associated with atypical cognitive abilities, which can have both disadvantageous and advantageous outcomes (Heilman 2005).
Owing to cultural and social pressures, many left-handed children were forced to write and perform other activities with their right hands. This conversion can cause multiple problems in the developing left-handed child, including learning disorders, dyslexia, stuttering and other speech disorders.
The other hand, comparatively often the weaker, less dextrous or simply less subjectively preferred, is called the non-dominant hand. In a study from 1975 on 7,688 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.
They are usually good at sports when in a one-on-one face-off. In games like baseball, boxing, fencing and tennis, left-handers often have an edge over their right-handed opponents who are used to playing with right-handed players mostly. Left-handers have typing advantages.
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.
Overall, individuals with ADHD had a 27.3 percent chance of being either left-handed or mixed-handed compared to 18.1 percent in the general population. So the results suggest that the effects are smaller than for the autism spectrum, but generally go in the same direction.
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.
Left Handedness in Research
In a study controlled for average intelligence (IQ), sex, and age, roughly 62% of those on the autism spectrum were not right-handed (i.e., they were more likely to be either left-handed, mix-handed, or of unclear handedness) compared to only 37% of the control sample population.
The left-handed child may be slower to grasp the concept of the hands moving round a clock face when learning to tell the time, and may find measuring or drawing lines using a ruler difficult, as the markings all start from the left side.
Some children experience them from early stages of literacy education, while others occur at a later stage while reading texts. In comparison to right-handed people, left-handed people are 2.5-3 times more likely to have difficulty in mastering written speech -- in both writing and reading.
But handedness has its roots in the brain—right-handed people have left-hemisphere-dominant brains and vice versa—and the lefties who claim Einstein weren't all that far off. While he was certainly right-handed, autopsies suggest his brain didn't reflect the typical left-side dominance in language and speech areas.
As demonstrated with her regal right-handed wave, our current monarch, Queen Elizabeth, is no southpaw — but plenty of her relatives/ancestors are/were. These include her great-grandmother Queen Victoria, her dad King George VI, her mum the Queen Mum, and her grandson, William.
Left-handers, rejoice! Marshall Bruce Mathers III (A.K.A. Eminem) is an esteemed member of your crew.
This indicates that if females had a chance of being left-handed of exactly 10 percent, males would have a 12 percent chance (the exact percentages vary a bit depending on geographical region). Given the low incidence of left-handedness in general, this 2 percent increase is quite a substantial difference.
Generally, left-handedness is found in 10.6% of the overall population. Some studies have reported that left-handedness is more common in twins than in singletons, occurring in 21% of people who are twins.
Sometimes people who are left-handed are called many different things, “Southpaws”, "Lefties", and other simply mean names, like "Weird" or "Strange".