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What makes people right-handed or left-handed?

Why are people left-handed or right-handed?
Why are people left-handed or right-handed? 03:04

MINNEAPOLIS — What do Lebron James, David Bowie and Bill Gates all have in common? They're left-handed. While they're a minority of the population, they're not alone. 

So why are we right- or left-handed? Good Question.

About 90% of people are right-handed, while 10% are left-handed. 

"Some of the theories think it's because of the way our brains are wired," Dr. Nancy Segal said.

Segal says lefties often have a more dominant right side of their brain while righties have a more dominant left side of their brain. Why is still a mystery.

"Language was a very important development in human history and of course, language is in the left hemisphere and that might strengthen the right hand," Segal said.

Studies show which hand is dominant may be influenced by genetics, adverse birth events or even random chance.

"Handedness does seem to have a genetic component that is inherited but there's no simple pathway from parent to child we're able to figure out," Segal said.

Dr. Nicola Grissom says evolution could also have a role.

"I think the best guess we have for left-handedness is that it provides that level of flexibility for future adaptation," she said. "If we needed our left hands for something we'd be kind of outta luck."

While left-handedness has become more accepted over the years. Lefties still live in a right-handed world, and that too is an influence.

"There's a long history of people being left-handed, training themselves to be right-handed because of them trying to work in a world that is set up for right-handed people," Grissom said.

Segal says there's no need to feel left out when lefties stand out.

"They may have certain attributes, certain ways of processing information that is unique and distinct so there may be some perks to being left-handed," Segal said. "Whenever you can distinguish yourself in a different way, I think that's not a bad thing."

Studies show left-handed parents are a little more likely to have twins. Yet twins, more often, have opposite handedness.

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