HANDEDNESS AND ITS INFLUENCE ON PERSONALITY
-Sai Lavanya Patnala, Final year, Apollo Medical College, Hyderabad
What is Handedness?
Handedness is an individual’s preferential use of one hand, due to it being stronger, faster or better in dexterity.
Ninety per cent of the human population has been right-handed since the Paleolithic, yet the genetic basis of handedness remain poorly characterized. 
Research has revealed that right-handers display more activation in the right hemisphere when using the left hand, than in the left hemisphere when using the right hand. It has been suggested that, for right handers to perform with their non-preferred, left hand, more effort is required 
In general, motor functions seem more strongly lateralized than sensory, emotional, and cognitive functions.
The fact that either the right or the left hemisphere can be dominant for motor function, resulting in either left- or right-handedness, seems to be a matter of natural variation. It remains unclear, however, why left-handedness is less common than right-handedness. From an evolutionary perspective, if neither of the two variants conferred any greater advantage than the other, a 50:50 distribution in the population would be expected
How is the handedness determined?
Handedness is thought to be partly hereditary.Left-handers are more likely to have left-handed parents, particularly left-handed mothers; this indicates possible maternal transmission.
The age of hand dominance has been debated for decades with the consensus maintaining that at about 5 years old children begin to have stability in hand preference (Bloodsworth, 1993; Gesell & Ames, 1947; Lewis et al., 1986; Tan, 1985).
Handedness probably begins to develop in the uterus: Fetuses suck the right thumb more often than the left, move the right arm more, and lie more often with the head turned to the right.
What disorders can be attributed to handedness?
In most cases, left-handedness appears to be the result of natural variation, but some types of handedness may be the expression of an early developmental disturbance or genetic defect.
There are well-established associations between left-handedness and several neurodevelopmental disorders (Brandler and Paracchini, 2014).There is a plethora of literature demonstrating a preponderance of left-handedness in an array of psychiatric disorders, including meta-analyses in schizophrenia (Hirnstein and Hugdahl, 2014), supporting the view that there is a genetic link between handedness, brain lateralization and schizophrenia (Berlim et al., 2003; Francks et al., 2007).
A study that correlated brain imaging phenotypes from ∼9000 UK Biobank participants with handedness found two loci associated with left-handedness (rs199512 and rs3094128) were also significantly associated with numerous mental health variables and with familial history of Parkinson’s disease in the genotyped UK Biobank participants.
Several studies have indicated an elevated frequency of left-handedness in children with Developmental Coordination Disorder (DCD)
What traits can be correlated with handedness?
Left-handedness is also more common among proficient musicians.Furthermore, left-handedness is unusually common among successful high-performance athletes, particularly in one-on-one sports such as tennis, boxing, and judo. Many examples from sporting history might be adduced on this point, e.g., Andreas Brehme’s goal scored with the left foot in the 1986 World cup quarter-final (Germany vs. Mexico) 
Certain types of left-handedness also display a statistically significant association with developmental delays like the onset of sexual maturity and secondary sexual characteristics.Left-handers tend to be shorter.
Orme ( 1970) suggested that left handers showed greater levels of emotional instability than right handers, while Hicks and Pel legrini (1978) found, using a student sample, that right handers were significantly less anxious than both left and mixed hander groups.
Older studies including Kalodner, Rodin, and Lester (1994) found that left-handed men scored lower than right-handed men on psychoticism. Only one study was found that measured the difference between the different degrees of handedness of left-handed and right-handed individuals with regards to depression scores. The depression scores were found to be higher for the mixed-left handed group (Bemporad, 1986).
Handedness arose early in evolution and has probably been constitutive for the development of higher cognitive functions. For instance, handedness may have provided the basis for the development of speech and fine motor skills, both of which have played a critical role in the evolution of mankind. Certain types of handedness seem to be associated with disease.
- Billiard S, Faurie C, Raymond M. Maintenance of handedness polymorphism in humans: a frequency-dependent selection model. J Theor Biol. 2005 Jul 7;235(1):85-93. DOI: 10.1016/j.jtbi.2004.12.021. PMID: 15833315. https://pubmed.ncbi.nlm.nih.gov/15833315/
- Jäncke L, Peters M, Schlaug G, Posse S, Steinmetz H, Müller-Gärtner H. Differential magnetic resonance signal change in human sensorimotor cortex to finger movements of different rate of the dominant and subdominant hand. Brain Res Cogn Brain Res. 1998 Apr;6(4):279-84. doi: 10.1016/s0926-6410(98)00003-2. PMID: 9593941. https://pubmed.ncbi.nlm.nih.gov/9593941/
- Akira Wiberg, Michael Ng, Yasser Al Omran, Fidel Alfaro-Almagro, Paul McCarthy, Jonathan Marchini, David L Bennett, Stephen Smith, Gwenaëlle Douaud, Dominic Furniss, Handedness, language areas, and neuropsychiatric diseases: insights from brain imaging and genetics, Brain, Volume 142, Issue 10, October 2019, Pages 2938–2947, https://doi.org/10.1093/brain/awz257
- Ghirlanda S, Frasnelli E, Vallortigara G. Intraspecific competition and coordination in the evolution of lateralization. Philos Trans R Soc Lond B Biol Sci. 2009;364:861–866.
- Gutwinski S, Löscher A, Mahler L, Kalbitzer J, Heinz A, Bermpohl F. Understanding left-handedness. Dtsch Arztebl Int. 2011 Dec;108(50):849-53. doi: 10.3238/arztebl.2011.0849. Epub 2011 Dec 16. PMID: 22259638; PMCID: PMC3258574.