Abstract
Handedness and brain asymmetry are widely regarded as unique to humans, and associated with complementary functions such as a left-brain specialization for language and logic and a right-brain specialization for creativity and intuition. In fact, asymmetries are widespread among animals, and support the gradual evolution of asymmetrical functions such as language and tool use. Handedness and brain asymmetry are inborn and under partial genetic control, although the gene or genes responsible are not well established. Cognitive and emotional difficulties are sometimes associated with departures from the "norm" of right-handedness and left-brain language dominance, more often with the absence of these asymmetries than their reversal.
Highlights
The most obvious sign that our brains function asymmetrically is the near-universal preference for the right hand, which goes back at least as far as the historical record takes us, and has long been a powerful source of symbolism, with the dexterous right associated with positive values and the sinister left with negative ones [1]
Since language itself is uniquely human, this reinforced the idea that brain asymmetry more generally is a distinctive mark of being human [3]
Across three independent samples of individuals with dyslexia, a genome-wide assay revealed the minor allele at the rs11855415 locus within this gene to be significantly associated with increased right-handedness [72]
Summary
The most obvious sign that our brains function asymmetrically is the near-universal preference for the right hand, which goes back at least as far as the historical record takes us, and has long been a powerful source of symbolism, with the dexterous right associated with positive values and the sinister left with negative ones [1]. In recent formulations of the X–Y theory, it has been proposed that handedness and cerebral asymmetry are facultative traits, universally encoded in the human genome, and that the variations giving rise to schizophrenia or anomalies of handedness and cerebral asymmetry are epigenetic, and not coded in the nucleotide sequence [86] It appears that epigenetic change through DNA methylation can be transmitted between generations [87], which might explain pedigree effects that are not detected in linkage analyses. Around twothirds of chimpanzees are right-handed, especially in gesturing [17] and throwing [18], and show left-sided enlargement in two cortical areas homologous to the main language areas in humans—namely, Broca’s area [19] and Wernicke’s area [20] (see Figure 1) These observations have been taken as evidence that language did not appear de novo in humans, as argued by Chomsky [21] and others, but evolved gradually through our primate lineage [22]. It is this productive aspect of language, rather than the mechanisms of understanding, that shows the more pronounced bias to the left hemisphere [37]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
