Gene For Left-handedness Identified in ScienceDaily. The original paper is LRRTM1 on chromosome 2p12 is a maternally suppressed gene that is associated paternally with handedness and schizophrenia:
Left-right asymmetrical brain function underlies much of human cognition, behavior and emotion. Abnormalities of cerebral asymmetry are associated with schizophrenia and other neuropsychiatric disorders. The molecular, developmental and evolutionary origins of human brain asymmetry are unknown. We found significant association of a haplotype upstream of the gene LRRTM1...with a quantitative measure of human handedness in a set of dyslexic siblings, when the haplotype was inherited paternally...While we were unable to find this effect in an epidemiological set of twin-based sibships, we did find that the same haplotype is overtransmitted paternally to individuals with schizophrenia/schizoaffective disorder...We then found direct confirmatory evidence that LRRTM1 is an imprinted gene in humans that shows a variable pattern of maternal downregulation. We also showed that LRRTM1 is expressed during the development of specific forebrain structures, and thus could influence neuronal differentiation and connectivity. This is the first potential genetic influence on human handedness to be identified, and the first putative genetic effect on variability in human brain asymmetry. LRRTM1 is a candidate gene for involvement in several common neurodevelopmental disorders, and may have played a role in human cognitive and behavioral evolution.
The paper seems to be alluding to a lot of separate and distinct facts which need to be glued together into a plausible causal system. In other words, more work needs to be done. Nevertheless, multiple genetic issues are highlighted, genomic imprinting, behavioral differences and evolutionary changes in the human lineage in regards to neurological organization. It shows how many different things may hinge on one genetic point of difference because of the interconnected nature of gene expression and development.
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It shows how many different things may hinge on one genetic point of difference because of the interconnected nature of gene expression and development.
And also that simple-minded explanations for why it's risen to whatever frequency it's at -- such as an advantage for southpaws in fistfights, something similar for chucking spears or using shields & swords -- should be treated with great skepticism. Better to look into it being collateral damage where the target is some cognitive or behavioral trait, as the abstract suggests.
yes. also, i wonder how accurate simply separating humans into "left handed" and "right handed" is. i write with my right hand, but for sports i'm more left handed (i can throw a football with either hand and switch hit, but i'm totally left handed and right footed in basketball).
They use an objective measurement of "handedness": "The test involved the measurement of the time taken by subjects to move, with each hand, a row of pegs on a board from one location to another." (link - a previous paper of theirs that is referenced, and apparently incorporated, in the Nature paper).
If sports skills were taken into account I would probably qualify as "no-handed"...
Apparently the handedness association with the haplotype is only detected among dyslexic children. Did I read that right? If so, looks like a deleterious gene that causes havoc in brain structure and only slightly favours left-handedness as a result...