Study Aims to Find Out Why Some People Are Left-handed

What do Lady Gaga, Barack Obama, and Bill Gates have in common – aside from their fame? They are all left-handed.

But why are 10 percent of people left-handed while most are right-handed?

Researchers are trying to find out.

A recent study identified a genetic cause of left-handedness in some people. Researchers found rare variants of a gene involved in controlling the shape of cells. They found the variants to be 2.7 times more common in left-handed people.

These genetic variants account for possibly 0.1 percent of left-handedness. But the researchers said a gene, called TUBB4B, might play a part in the development of brain asymmetry.

In most people, the two halves, or hemispheres, of the brain have slightly different structures and are dominant for different activities.

"For example, most people have left-hemisphere dominance for language, and right-hemisphere dominance for tasks that require directing visual attention to a location in space," said Clyde Francks of the Max Planck Institute for Psycholinguistics in the Netherlands. Francks was the top writer of the study published recently in Nature Communications.

Francks suggested that for most people, the left side of the brain controls the dominant right hand. "The nerve fibers cross from left-to-right in the lower part of the brain," Francks said. He added, "In left-handers, the right hemisphere is in control of the dominant hand. The question is: what causes the asymmetry of the brain to develop differently in left-handers?"

TUBB4B controls a protein that gets formed into filaments called microtubules. These microtubules give structure to the insides of cells. The changes in TUBB4B that are more common in left-handers suggest that microtubules are involved in setting up the brain's normal asymmetries, Francks said.

The two brain hemispheres start to develop differently in the human embryo. Scientists do not know the mechanism that controls this.

"Rare genetic variants in just a handful of people can pinpoint genes that give clues to developmental mechanisms of brain asymmetry in everyone," Francks added. TUBB4B is an example.

The study's findings were based on genetic data from more than 350,000 middle-aged to older adults in Britain. It was from the UK Biobank. About 11 percent of the people involved were left-handed.

For most people, left- or right-handedness might come down to chance. Changes in the levels of some molecules during important times of brain development could influence it, Francks suggested.

Historically, many cultures disapproved of left-handedness and forced people to become right-handed.

In English, the word "right" also means "correct" or "proper." And the expression a "left-handed compliment" means that a comment might seem nice but is an insult.

The levels of left-handedness differ around the world, with lower rates in Africa, Asia and the Middle East compared to Europe and North America, Francks said.

"This likely reflects suppression of left-handedness in some cultures - making left-handed kids switch to right-handedness, which also used to happen in Europe and North America," Francks added.

The new findings might have use in the field of mental health. People with schizophrenia are around twice as likely to be left-handed or ambidextrous. People with autism are around three times as likely, Francks said.

He observed that genes involved in developing the brain in early life might be involved in brain asymmetry and mental health.

"Our study found suggestive evidence of this, and we have also seen it in previous studies where we looked at more common genetic variants in the population," Francks added.

I'm John Russell.

Will Dunham reported on this story for Reuters. John Russell adapted it for VOA Learning English.

_____________________________________________

variant – n. different in some way from others of the same kind

asymmetry – n. having two sides or halves that are not the same

dominant –adj. having the most control, strength or ability to influence

fiber –n. a long, thin piece of material that has strength to it

filament – n. a long thread made of proteins

mechanism – n. a process or system produces a particular result

ambidextrous – adj. able to use both hands equally well