Study: Why are some people left-handed while most are right-handed?

What do Lady Gaga, Barack Obama, Bill Gates, Paul McCartney, Justin Bieber, Jimi Hendrix, Judy Garland and David Bowie have in common? All of them are left-handed, which accounts for 10 percent of the population.

But why do some use their left hand and most use their right?

A new study sheds light on the genetic component responsible for left-handedness in some people. The researchers identified rare mutations in a gene involved in determining the shape of cells, and found that they were 2.7 times more common in left-handed individuals.

While these genetic changes represent only a small fraction, perhaps 0.1 percent, of the causes of left-handedness, the study shows that this gene, called TUBP4B, may play a role in the development of so-called left-handedness, the researchers said. Brain symmetry, which determines the dominant hand.

Brain asymmetry

In most humans, the two parts of the brain have slightly different anatomical structures and are responsible for different functions.

“For example, the left hemisphere of the brain dominates language in most humans, while the right hemisphere performs right-handed tasks that direct visual attention to a location.

And, “In most people, the left hemisphere controls the dominant right hand. The associated nerve fibers run from left to right in the lower part of the brain. In left-handed people, the right hemisphere controls the dominant hand.”

“The question is, 'What causes brain asymmetry to develop differently in left-handed people?'

The TUPB4B gene controls a protein that melts into filaments called microtubules, which provide the internal structure of cells. Identifying rare mutations in this gene, more common in left-handed people, suggests that microtubules are involved in the formation of normal brain asymmetries, said Bronx.

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Rare genetic mutations

The two hemispheres of the brain begin to develop differently in embryos, but the mechanism of their development is not clear.

“Rare genetic mutations in a small number of people can determine genes involved in the mechanisms of brain asymmetric development in all humans. The TUBB4B gene is a good example of this,” Franks added.

The results are based on genetic data from more than 350,000 middle-aged and elderly people in Britain, 11 percent of whom are left-handed.

The determination of the dominant hand in most people is probably the result of chance.

“We believe that most left-handedness is the result of random variation during fetal brain development, independent of genetic influences or the influence of the surrounding community,” Franks said. “For example, random fluctuations in the concentrations of certain molecules during key stages of brain development.”

Many cultures over the centuries have denigrated left-handedness and tried to force left-handed people to use their right hands. In English, the word “right” also means “to the right” or “appropriate”, and the word “right” is derived from the Latin word meaning “on the left side”.

Cultural and psychological influences

Compared to Europe and North America, the prevalence of left-handedness varies in different parts of the world in Africa, Asia and the Middle East, Bronx said.

“This reflects the suppression of left-handedness in some cultures, causing left-handed children to switch to right-handedness, which is also happening in Europe and North America,” he added.

New findings may be used in the field of psychiatry. Franks says that while most people with left-handedness do not suffer from psychological problems, people with schizophrenia are twice as likely to be left-handed or both, and people with autism are three times more likely.

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Franks added, “Some genes that play a role in early brain development may play a role in asymmetry and psychological traits. Our study found evidence to suggest this, and we've seen it in previous studies that looked at more common genetic changes.”

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