Medea factors or genes are maternal-effects mechanisms, found in many species, in which the mother's body selectively kills embryos of a certain genotype. Humans have a similar genetic mechanism, the gene RHD which produces Rh-factor involved in blood type. Recently it was proposed that RHD acts as a maternal-effects gene that determines handedness (i.e., right handed or non-right handed) in individuals of our species.
Asymmetry in brain lateralization is a common trait among vertebrates, including mammals.Cerebral asymmetries are well documented in humans; in particular, handedness preference (i.e., right handed or non-right handed) and in the language-related areas of the brain (i.e., cerebral or speech laterality, right-brained or left-brained language dominance). Amar Klar argued that the gene that determines handedness in humans is related to hair-whorl rotation (i.e., the direction the hair spins at the back of the head, either clockwise or counterclockwise), although this gene remains to be identified.
Klar showed that hair-whorl rotation was related to sexual orientation, Klar implicated this same gene in schizophrenia and bipolar disorder, and other researchers showed that hair-whorl rotation was related to speech laterality. Klar also argued that the handedness gene is involved in speech laterality and may be involved in speech dyslexia. Furthermore, treatment for RHD maternal-fetal genotype incompatibility, which allows more fetuses to survive to term now, may be one explanation why ASD appears to be increasing in frequency if RHD is indeed the handedness gene, although many other mechanisms, both genetic and environmental, have also been suggested for the increase in prevalence.
Many of these children may not have survived in the past, but now most of them survive due to treatment of Rh- mothers for maternal-fetal genotype incompatibility to prevent death or harm to their Rh+ fetuses. Thus, if RHD is the handedness gene and as such is involved in ASD, then it gives another explanation why ASD appears to be increasing in some human populations. One wonders if the other alternative phenotypes (e.g., bipolar disorder) have also been increasing in frequency in our species.
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