6.8.2. How It Works (3)
It is plausible that only the one hand (the right) was used for a more efficient and simple way of communicating. This would explain why language and hand dominance are on the same side (remember, the left side of the brain controls the right side of the body, so left-language dominance and right-hand dominance are both due to the left side of the brain).
If this were the norm during evolution, it may help to explain why most left-handers still have speech areas in the left hemisphere. However, this still doesn’t answer the question of why the right hand was dominant in the beginning. At present, this can be only speculation; the important point is that right- and left-handedness are distributed differentlythey are not mirror images of each other, which has implications for the genetics of handedness and the laterality of other functions.
It has been argued that the original hand preferences evolved from a postural position preference of the right hand and consequently a left preference for reaching in arboreal (tree-living) species.8 So, with postural demands becoming less pronounced in ground-dwelling species, the left hand remained the dominant one for highly stereotyped tasks like simple reaching, whereas the right became the preferred one for more manipulative tasks or tasks requiring some skill. In other words, we would hang on with the left hand and pick fruit with the right.
Although this is an interesting theory for why the majority of the population is right-handed, it does not give any indication as to why some people are left-handed. Are left-handed people highly skilled in reaching? Are left-handed people as skilled in manipulative tasks as their right-handed counterparts? Regretfully, these questions have to wait for further research.
6.8.3. End Notes
Salive, M. E., Guralink, J. M., & Glynn, R. J. (1993). Left-handedness and mortality. American Journal of Public Health, 83, 265-267.
Annet, M. (1972). The distribution of manual asymmetry. The British Journal of Psychology, 63, 343-358.
Hartlage, L. C., & Gage, R. (1997). Unimanual performance as a measure of laterality. Neuropsyhological Review, 7(3), 143-156.
Bakan, P. (1971). Handedness and birth order. Nature, 229, 195.
Davidson, R. J., & Hugdahl, K (eds.) (1995). Brain Asymmetry. Cambridge, MA: MIT Press.
Rasmussen, T., & Milner, B. (1977). The role of early left-brain injury in determining lateralization of cerebral speech functions. Annuls of the New York Academy of Sciences, 299, 355-369.
Rizzolatti, G., & Arbib, A. (1998). Language within our grasp. Trends in Neurosciences, 21, 188-194.
MacNeilage, P. E. (1990). The “Postural Origins” theory of primate neurobiological asymmetries. In N. A. Krasneger et al. (eds.), Biological and Behavioural Determinants of Language Development, 165-168, Hillsdale, NJ: Erlbaum.
6.8.4. See Also
Laska, M. (1996). Manual laterality in spider monkeys (Ateles geoffroyi) solving visually and tactually guided food-reaching tasks. Cortex, 32(4), 717-726.
Karen Bunday
Taken from : Mind Hacks
