Why are most people right-handed and only 10% left-handed?

In the past, left-handed people were not always treated well. They are miserable because of this penchant and are assigned to bad things or even called witches.

In fact, the word "sinister" comes from the word "left" or "left hand".

Over the past several decades, some hypotheses have been made about why some left-handed people, including an outdated idea, are related to mothers being stressed during pregnancy. .

Causes in the spinal cord - not the brain

Since the 1980s, scientists have found that our left-handed or right-handed are more likely to be identified before we are born - according to the ultrasound shown, it appears during pregnancy. Only 8 weeks old. From the 13th week, the fetus tends to suck the right or left hand in the uterus.

In the past, it was thought that the difference between the left hemisphere and the right hemisphere determines the left or right-handed man. But a study published last year in eLife magazine found that the answer lies in the spinal cord.

The study was conducted by Sebastian Ocklenburg, Judith Schmitz, and Onur Gunturkun at the Ruhr University Bochum with other colleagues in the Netherlands and South Africa. The team found that the asymmetric gene activity of the uterine spinal cord could cause people to be left-handed or right-handed.

Only 10% of humanity is left-handed.(Photo: iStock).

Movement of arms and hands begins in the brain in an area called the motor cortex , which sends a signal to the spinal cord and then the signal is converted into movement.

The researchers found that when the fetus developed in the womb until about the 15th week, the cortex of the motor and spinal cord remained unconnected, but it was determined that the fetus was right-handed or left-handed. .

In other words, the fetus can move and choose a favorite hand before the brain begins to control the body.

To study this, the scientists analyzed gene expression in the spinal cord from the 8 th to 12 th week of pregnancy. They found significant differences in the left and right parts of the spinal cord that control the movement of the arms and legs.

Scientists conclude that the asymmetry of the spinal cord can lead to a phenomenon called epigenetic genetics , or phenomenon of organisms affected by changes in expression. genes not by their genes.

These changes often come from environmental influences and can affect how the fetus grows. Differences in these gene expressions have different effects on the right and left side of the spinal cord, leading to left-handed or right-handed.

So why are left-handed people so rare?

Scientists have long tried to explain this.

In 2012, researchers at Northwestern University developed a mathematical model to show that the percentage of left-handed people is the result of human evolution - in particular, the balance between cooperation and competition.

In other words, they think that, although the foundation of left-handed or right-handed is related to genetics, there is a social element that explains the proportional difference between left-handed and right-handed people.

Former US President Barack Obama uses his left hand to sign.

Daniel Abrams, assistant professor at McCormick School of Engineering and Applied Science and who helped develop this model, said : 'In a society where cooperation is highly valued, if animals are The bigger the society, the more likely the population will be on one side. The most important factor to create an effective society is the high level of cooperation. This leads to the majority of right-handed people ".

In other words, evolution has given priority to right-handedness, so anyone who deviates from this bias can still use his right hand despite their genetic predisposition. it has to be.

Judith Schmitz, one of the authors of the new study, said in the press that studies of twins show that the rate of genetics affecting forehand is about 25%.

New research cannot explain why most humans are right-handed, but bird studies suggest that genetics and the environment may be the cause, according to Judith Schmitz.

"In chickens and pigeons, genetic factors determine the position of eggs before hatching - their embryos are rolled so that the right eye is directed at the dim part of the eggshell and the left eye is the embryo's body. wrapped up, " she said.

The right eye of the dove is better than the left eye.(Photo: Skvty)

'Therefore, the eye must be stimulated by light before hatching, while the left eye is almost not exposed to light. The combination of genetic and environmental factors (light) causes visual asymmetry. The right eye of the pigeon and the chicken distinguishes, classifies and remembers the models better than their left eye. If chicken eggs or pigeon eggs are incubated in the dark, the development of this asymmetric phenomenon will not happen ".

The reason for left-handed people is still a bit mysterious - in part because scientific studies often overlook left-handed people, and it's hard to predict whether a child will be left-handed or right-handed first. when they are born.

But we know one thing, neurological differences between left-handed and right-handed people are very small , and they seem to have no effect on their behavior.