Only around one out of ten people in the world are left-handed, and the rest are already right-handed. Psychology Today said that it is about 10.6% of the whole population or only about 827 million people out of 7.8 billion people on Earth.
This is called hand dominance, and various theories have already tried to explain why there are left-handed people with most evidence pointing to genetic influence and others due to the left-brain and right-brain dominance.
Being left-handed is already determined even before the person is born. According to a 2017 study, hand dominance is already predicted during the first 15 weeks of pregnancy, where there are gene expression asymmetries in the spinal cord.
Negative Treatment Towards Left-Handed People in the Past
Although left-handed people are treated nicely today, those who lived in the past were not that fortunate, especially during the Medieval period. Left-handedness was associated with massive stigmas branding those people as unclean or witches, according to the Smithsonian Magazine.
Left-handed in the past is accused of being possessed by the evil spirits after all, the word "left" means sinister. These accusations likely stemmed from the idea that since the majority are right-handed, then everyone who deviates from it is evil.
But the world has gotten better and has accepted the left-handed people. However, there are still some undeniable bummers associated with being a left-handed person like the spiral notebooks, right-handed scissors and desks, and many more.
Left-Handed Since a Fetus
For years, scientists speculate that what makes people left-handed is caused by a single gene that controls the left-right preference in humans. However, they could not pinpoint the exact gene that does the job.
A 2017 study published in eLife suggests that left-handedness started in the spinal cord where the researchers found the gene expression asymmetries, Health Digest reported.
The left and right regions of the brain determine hand and arm movements. According to the study, being right- or left-handed is determined even when the person was still a 15-week-old fetus, a time before the connection between the spinal cord and motor cortex happened.
That means even as fetus people choose whether to use their left or right hand or thumbs for sucking before their brain has even sent a signal.
The researchers were able to come up with the conclusion after examining the gene expression in the spinal cord from the 8th to 12th of pregnancy. They said that they found differences in the right and left segments of the spinal cord that are responsible for controlling movements of the legs and arms, the reason why someone may be right-handed or left-handed.
Therefore, the researchers concluded that being a righty or a lefty was already predetermined before a person is born and even before the motor cortex and spinal cord are connected.
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