Hand preference

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. Men are slightly more likely to express a strongly dominant left hand than women. Right-handedness is the most common form, and it is estimated that around 90% of the world’s population is right-handed.Studies in the U.K., U.S. and Australia have revealed that left-handed people differ from right-handers by only one IQ point, which is not noteworthy ... Left-handers' brains are structured differently from right-handers' in ways that can allow them to process language, spatial relations and emotions in more diverse and potentially creative ways. Also, 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, even among those who played instruments that seem designed for right-handers, such as violins. Similarly, studies of adolescents who took tests to assess mathematical giftedness found many more left-handers in the population.One advantage is a left-handed catcher's ability to frame a right-handed pitcher's breaking balls. A right-handed catcher catches a right-hander's breaking ball across his body, with his glove moving out of the strike zone. A left-handed catcher would be able to catch the pitch moving into the strike zone and create a better target for the umpire. 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. Men are slightly more likely to express a strongly dominant left hand than women. Right-handedness is the most common form, and it is estimated that around 90% of the world’s population is right-handed. 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. 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. However, the growing weight of evidence from linkage and genome-wide association studies suggests that genetic variance in handedness cannot be explained by a single genetic locus. From these studies McManus et al. now conclude that handedness is polygenic and estimate that at least 40 loci contribute to determining this trait. 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). Twin studies indicate that genetic factors explain 25% of the variance in handedness, while environmental factors explain the remaining 75%. While the molecular basis of handedness epigenetics is largely unclear, Ocklenburg et al. 2017 found that asymmetric methylation of CpG sites plays a key role for gene expression asymmetries that have been related to handedness.