Link: http://www.bbc.com/future/story/20141215-why-are-most-of-us-right-handed
by Jason G. Goldman BBC
Published: December 16, 2014
Summary:
Around 85% of humans have a right hand dominance over left handedness, in no instances is left-handedness more prevalent than right handedness. A bias of one side chosen over the other in the use of our limbs begins in the brain, with the left hemisphere controlling the right side of the body, where most large tasks are controlled. The division of neurological labor over hemispheres of the brain is a feature that evolved in most animals over time as a way to carry out multiple tasks at the same time. For instance, it is possible that the left hemisphere became responsible through evolution to carry out routine tasks, such as foraging for food and react to changes in the environment. It has been suggested that when homo sapiens evolved to stand on two legs, their hands became free to develop different sets of skills, resulting in a "strengthening asymmetry" for using tools and performing tasks. This is supported by the fact that when chimps stand on all fours, they show no hand preference. Also, stone tools made 1.5 million years ago, show species wide right-handedness.
This article connects directly to the study of evolution and certain traits evolving to become dominant over others as species adapt to their environment. As human evolution progressed, we began to stand on two legs, which freed up our hands for specified tasks. Through this evolutionary trait, the dominance of one hand over the other evolved in a clear pattern of right-handedness over left-handedness. This particular trait is very interesting because the evolution of the trait is mostly unknown because left-handedness has been shown to not be a drawback in an individuals ability to function. This brings up the question of why right hand dominance has emerged to be much more prevalent than left hand dominance.
Why does the brain usually favor the left side (to control the right) rather than the right side (to control the left)?
ReplyDeleteBoth hemispheres are responsible for different tasks, the left side controls motor skills and other coordinative actions while the right side is focused on processing information, so its not so much that the brain prefers one side, just that they handle different responsibilities. This is why when the left hemisphere controls the right side of the body, we tend to favor that side for movement whereas the right hemisphere is generally more focused on information processing rather than fine motor movement such as hand dominance. This is not a hard and fast rule, but it has proved to be prevalent throughout the history of human adaptation.
DeleteWe often talk of how some traits that are more common in our society are, in fact, recessive. Is right-handedness a dominant or recessive trait?
ReplyDeleteHand dominance or preference has been observed to be a heritable trait so it would make sense to see it as either a dominant or recessive attribute, however, it has been shown that hand dominance is a polygenic trait with multiple genetic factors determining the phenotypical display of hand dominance. Much of a disposition towards right hand dominance, or left hand dominance has to do with the asymmetrical distribution of the brains two hemispheres and how it processes information. For this reason, hand dominance is not linked to a single dominant or recessive trait, but multiple factors and gene loci working simultaneously towards the phenotype.
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