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Better performance or individual preference for use of
Get Handedness essential facts below. View Videos or join the Handedness discussion. Add Handedness to your PopFlock.com topic list for future reference or share this resource on social media.
Better performance or individual preference for use of a hand
In human biology, handedness is a better, faster, or more precise performance or individual preference for use of a hand, known as the dominant hand. The incapable, less capable or less preferred hand is called the non-dominant hand. Right-handedness is the most common form, and it is estimated that around 90% of the world's population is right-handed. Handedness is often defined by which hand one writes with, as it is fairly common for people to prefer to do some tasks with each hand. However, true mixed-handedness is rare, as most people clearly prefer one hand for most purposes.
Most of the current research would suggest 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 a right-handed person, which makes their use by left-handed people more difficult. In many countries across the world, left-handed people are or were required to write with their right hand. However, left-handed people have an advantage in sports that involve aiming at a target, because their opponents will be more accustomed to the right-handed majority. As a result, they are over-represented in baseball, tennis, fencing, cricket, and boxing.
Right-handedness is by far the most common type. Right-handed people are more skillful with their right hands when performing tasks. Studies suggest that approximately 90% of the world population is right-handed.
Left-handedness is far less common than right-handedness. Left-handed people are more skillful with their left hands when performing tasks. Studies suggest that approximately 10% of the world population is left-handed.
Cross-dominance or mixed-handedness is the change of hand preference between tasks. This is very uncommon in the population with about a 1% prevalence.
Ambidexterity, equal ability to use both hands, is exceptionally rare. A completely ambidextrous person is able to do any task equally well with either hand. Those who learn it still tend to favor their originally dominant hand.
There are several theories of how handedness develops in individual humans. Occurrences during prenatal development may be important; researchers studied fetuses in utero and determined that handedness in the womb was a very accurate predictor of handedness after birth. In a 2013 study, 39% of infants (6 to 14 months) and 97% of toddlers (18 to 24 months) demonstrated a hand preference.
Division of labor
One common theory as to how handedness affects the hemispheres is the brain hemisphere division of labor. Since speaking and handiwork require fine motor skills, its presumption is that it would be more efficient to have one brain hemisphere do both, rather than having it divided up. Since in most people, the left side of the brain controls speaking, right-handedness predominates. This theory also predicts that left-handed people have a reversed brain division of labor.
Verbal processing in right-handed individuals takes place mostly in the left hemisphere, whereas visuospatial processing is mostly done in the opposite hemisphere. Left-handed individuals have a heterogeneous brain organization in which their brain hemispheres are either organized in the same way as right-handers (but with the hemispheres reversed) or even such that both hemispheres are used for verbal processing. When the average is taken across all types of left-handedness, it shows that left-handers are less lateralized.
Handedness displays a complex inheritance pattern. For example, if both parents of a child are left-handed, there is a 26% chance of that child being left-handed. A large study of twins from 25,732 families by Medland et al. (2006) has indicated that the heritability of handedness is roughly 24%.
To date, two theoretical single gene models have been proposed to explain the patterns of inheritance of handedness, the first by Marian Annett of the University of Leicester and the second by Chris McManus of UCL.
Brandler et al. performed a genome-wide association study for a measure of relative hand skill and found that genes involved in the determination of left/right asymmetry in the body play a key role in determining handedness. These results suggest the same mechanisms that determine left/right asymmetry in the body (e.g. Nodal signaling and ciliogenesis) also play a role in the development of brain asymmetry (handedness is an outward reflection of brain asymmetry for motor function).
In 2019, Wiberg et al. performed a genome-wide association study and found that handedness was significantly associated with four loci. Three of these loci are in genes encoding proteins involved in brain development.
Twin studies indicate that genetic factors explain 25% of th