Why People Are Left Handed

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There have been more right-handed people than left-handed since 500,000 years ago. In many cultures throughout the world, left-handed people have been forced to give up what is natural and use their right hands instead of the left. With that knowledge, people might wonder what makes a person left-handed to begin with?

Recent research by Oxford University shows a genetic difference between left and right-handed people. Before this information was revealed in September 2019, it was thought handedness depended on 75% of the environment and 25% of a human’s DNA, unsure of which parts of the DNA even affected it. However, this new information reveals the reason for left-handedness.

 400,000 people were tested, 38,332 being left-handed, for their different biological genomes. Researchers found that four proteins in genetic code, three of which influenced early brain development and the architecture of the brain, primarily affected the microtubules which are a part of the scaffold of the cell. This scaffold, scientifically called the cytoskeleton, directly affects how a cell’s structure forms and how that one particular cell works together with the rest of the body. Scientists have seen how cytoskeletons of cells affect other animals in the past, especially regarding left to right asymmetry and preference of hand choice. Gwenaëlle Douaud, a senior author for the experiment, stated that “Many animals show left-right asymmetry in their development, such as snail shells coiling to the left or right,” referencing to the cytoskeletons. 

The research team also found out that the differences in a person’s white matter tracts also affect handedness. White matter is the substance in the brain that allows the different parts of the brain to communicate with each other. After special review of 10,000 of the tested people’s brain scans, the team found a significant difference in the brain’s white matter. Left-handed people had more developed white matter tracts in the language section of the brain, located on the left side. This left side of the brain controls all movements on the right side of the body, and vice versa with the brain’s right side. This means the left hand is controlled by the right side of the brain. As a result of this, left-handed people must have a stronger connection with the left language-oriented parts of their brain and their right brain, which controls the left hand, in order for it to function well together. 

As a result, the left-handed people seemed to have a brain that could work more efficiently. Donaud said that lefties had, “a higher synchronization of the natural oscillations of your brain… precisely … in the brain regions dedicated to language.” An oscillation is a firing of electrical messages in the brain resulting from an event in a person’s environment. 

However, being a lefty comes with costs. Although lefties are less prone to get Parkinson’s disease, there is a higher chance of getting schizophrenia. Researchers don’t think that these are a cause of being left-handed. In the release of their research, emphasized that handedness wasn’t a cause. Instead, there was a correlation between the two.

The researchers hope to do more research left-handedness in the future. They believe they have only just scratched the surface, finding only the first percent of the 25% of the genetics that makes people left-handed. They hope that future research will focus on the effects of left-handedness and dig down deeper into what truly genetically makes a lefty.

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