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Here’s Why Some People Are Left-Handed


Image credit: Evgeny Dubinchuk/shutterstock

It appears that almost daily necessities, such as can openers, scissors, and spiral bound notebooks are usually designed for right-handed people. Scientists have been making efforts to figure out the basis for handedness; however we are still not sure about the real reason behind it. Perhaps, it is quite simple that such puzzle is so amazing that it makes us feel fascinating to know more about it. Actually one thing is certain that nearly one in 10 people are left-handed

This statistic is widely known to almost every country in the world. It is seemingly quite true that about ten percent of whole population is always lefties. Therefore there is kind of implication that a genetic basis does exist for the behavior. In his talk to the Royal SocietySilvia Paracchini, a geneticist from the University of St. Andrews, said that it was not the simple question of black and white.

When scientists are intended to find out the genetic basis closely linked with a trait, they often resort to twins. The use of twins shows the importance of separating common factors in genetics and environment, which could have impact on the trait of interest, because twins are frequently brought up in the same household. In researches related to twins, scientists have discovered that only about 25% of handedness could be attributed to a person’s genes. As Paracchini claimed, it was surprisingly low. However, the result of more studies in this field has also proved that it is amazingly consistent as well.

Over the past decades, it has been assumed that there should be a gene directly accountable for handedness; however scientists have found no realistic approach to testing such existence. Although the data set has been increasingly huge due to current sequence of more than 100,000 human genomes, scientists are still uncertain about a single factor that could directly identify handedness.

However, some progress has been made. As Paracchini was focusing on the genetic basis of dyslexia, one of her PhD students discovered something else: that is an association between handedness and the same gene that sets up the bodies left/right axis. The particular gene is accountable for the condition situs inversus, in which the asymmetry of the body is switched; leading to the fact the heart is normally on the right, instead of being on the left.

This makes it possible that the same system controlling the structural asymmetry of human body plan could be recycled and used for controlling behavioral asymmetry. Although scientists think that an association exists, they have no clear idea about whether there is a link.

To muddy the waters much more, another study focused on the rate of left handedness in patients with situs inversus has discovered that there is no difference in comparison with normal people. But, as Paracchini said, if there was a link between the two conditions, it would be a small and unimportant fraction in the underlying genetics of handedness.

Source: Science alert