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Raise your hand if you're a lefty!

Aug. 13 marks the 22nd annual International Left-Handers Day, an event that celebrates the uniqueness of left-handed people.

Why are people left-handed?

Roughly 10% of the population primarily use their left hand. This happens because the brain is divided into two hemispheres. The right side of the brain controls movement on the left side of the body and vice versa.

But why humans develop "handedness," or a preference for one side over the other, is still somewhat a mystery.

Because left-handedness tends to run in families, scientists believed for years that handedness was linked to a gene, but could not identify the exact one, according to The New York Times.

A 2013 study published in PLOS Genetics found that a network of genes may determine a person's handedness, as opposed to just one. "In reality, the research suggests that handedness could be more subtle than simple 'dominant' or 'recessive' traits – a whole host of genes might play significant roles," Natasha Geiling wrote about the study on Smithsonian.com.

Photos of famous lefties:

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Three fun facts about lefties

1. Three of the last four presidents have been left-handed: President Obama, President George H.W. Bush and President Clinton.

2. The percentage of left-handed people (about 10% of the population) to right-handed people has stayed consistent over time. That includes studies of handprints on ancient cave paintings and analysis of ancient artifacts, according to The New York Times.

3. LOOGY in baseball stands for "left-handed, one-out guy." It's a term for a relief pitcher who throws left-handed and specializes in pitching to left-handed batters.

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