Sounds simple enough, but the devil is in the details. Questionnaires, like the Edinburgh Handedness Inventory, exist, sure, but some of their questions can rapidly become outdated. Ask a Millennial which hand they typically use to strike a match and you might be met with a confused face. Also, just because you write with your left hand does not mean you throw a ball with the same hand.
This also brings up the issue of preference versus skill. You may prefer engaging in a manual task with your left hand, but in a test you may be revealed to be more skilled with your right hand. In fact, nearly a third of left-handed writers throw more accurately with their right hand and a tiny percentage of right-handed writers throw best with their left. Another kink to the story: when you ask Baby Boomers which hand they use to write, you might get deceptive numbers if your interest is in the underlying biology of handedness.
Thus people born as left-handers were culturally forced to become right-handers. Nearly 1 in 10 people worldwide reported using their left hand to write, with some variation from country to country. This was somewhat confirmed by an analysis of nearly 2. Marsupials who hop around on their hind legs, like the prototypical kangaroo, are actually more likely to prefer their left forelimb or arm. Other animals seem to show a preference for one wing or paw over the other, but this choice is inconsistent across or within species.
In having a consistent preference for the right hand, humans are quite unique in the animal kingdom to the best of our knowledge. Sinistral preference is shrouded in its own growing mythology. Studies published over the years have seemingly shown that more left-handed people than expected are diagnosed with a large number of diseases, from autoimmune conditions to psychiatric disorders. This led scientists to wonder if common biological pathways were involved. Often they can be traced back to an unfortunate bit of publication bias.
Whether or not someone is left-handed is a quick bonus question a researcher can throw into a survey. This is an example of bad science and not the only one as far as handedness is concerned. You may have heard that, on average, left-handed people die seven years younger than right-handed people.
This is not true. It comes from a poorly analyzed dataset derived from a baseball encyclopedia and published in the journal Nature in An equally flawed assessment published a few years later claimed the gap was nine years. Yet the myth persists, in part because of its wide coverage in the media, its shock value, and its memorability.
The C gene is less likely to occur within the gene pool, but when it is present, the hand preference of the individual with the C gene is determined randomly. Individuals with the C gene will have a 50 percent chance of being right-handed and a 50 percent chance of being left-handed. These theories of hand preference causation are intriguing because they can account for the fact that the side of hand preference of individuals with the C gene most left-handers and some right-handers can be influenced by external cultural and societal pressures, a phenomenon that researchers have documented.
These theories can also explain the presence of right-handed children in families with left-handed parents and the presence of left-handed children in families with right-handed parents. If the familial genetic pool contains C genes, then hand preference becomes amenable to chance influences, including the pressures of familial training and other environmental interventions that favor the use of one hand over the other. The proposed genetic locus that determines hand preference contains an allele from each parent, and the various possible genetic combinations are DD individuals who are strongly right-handed, DC individuals who are also mostly right-handed, and CC individuals who are either right-handed or left-handed.
These genetic combinations leave us with an overwhelming majority of human right-handers and a small, but persistently occurring, minority of left-handers. Already a subscriber? Sign in. Thanks for reading Scientific American. Handedness, or hand preference, is the tendency to be more skilled and comfortable using one hand instead of the other for tasks such as writing and throwing a ball.
Although the percentage varies by culture, in Western countries 85 to 90 percent of people are right-handed and 10 to 15 percent of people are left-handed. Mixed-handedness preferring different hands for different tasks and ambidextrousness the ability to perform tasks equally well with either hand are uncommon. Hand preference begins to develop before birth. It becomes increasingly apparent in early childhood and tends to be consistent throughout life.
However, little is known about its biological basis. 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. The right hemisphere controls movement on the left side of the body, while the left hemisphere controls movement on the right side of the body.
It was initially thought that a single gene controlled handedness. However, more recent studies suggest that multiple genes, perhaps up to 40, contribute to this trait.
Each of these genes likely has a weak effect by itself, but together they play a significant role in establishing hand preference. Studies suggest that at least some of these genes help determine the overall right-left asymmetry of the body starting in the earliest stages of development. So far, researchers have identified only a few of the many genes thought to influence handedness. For example, the PCSK6 gene has been associated with an increased likelihood of being right-handed in people with the psychiatric disorder schizophrenia.
Another gene, LRRTM1 , has been associated with an increased chance of being left-handed in people with dyslexia a condition that causes difficulty with reading and spelling. It is unclear whether either of these genes is related to handedness in people without these conditions.
Studies suggest that other factors also contribute to handedness. The prenatal environment and cultural influences may play a role.
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