This boy is likely left-hand dominant.

Think fast: Which hand do you use to write? Which do you use to brush your teeth or throw a ball? Most people use their right hand for these tasks. That's because for most of the population the right side of the body is dominant, so the right hand is the one they use most often, while the left remains the non-dominant hand.

Still, lefties are a loud and proud bunch. Former President Barack Obama was a leftie, as are Bill Gates and Oprah Winfrey. Although left-handed individuals have been persecuted throughout history, there are no disadvantages to being left handed.

People can't chose which side of their body is dominant, and most people give little thought to it, but understanding dominant vs. non-dominant hand gives an interesting glimpse into human biology.

Why Do Humans Have A Dominant vs. Non-Dominant Hand?

It seems strange that humans have two hands, but one that functions better than the other. Dominant hands are generally stronger and have faster reaction times, so there is a theory that having a dominant side reduces reaction time, since your brain doesn't have to chose which hand to use. It automatically goes to the stronger side. Surprisingly, humans aren't alone in having a dominant hand. Other mammals show preference for one side as well.

No one knows why humans have one dominant side, but scientists are starting to understand what makes a person a righty or a leftie. The reason lies in the brain, scientists believe. The left side of the brain controls language and speech, and natural selection has favored people who have a strong left side. Because the left side of the brain controls the right side of the body, the majority of the population (between 85 and 90 percent) are right-handed, and only a small minority of people are left-handed.

Why Are Some People Left-Handed?

Despite the fact that most people are right-handed, a sizable part of the population still uses their left hands. People who are left-handed usually have the hemispheres of their brains on the opposite side that would be expected. This means that the dominant hemisphere, which controls language and speech, is on the right side of the brain and thus controls the left hand.

Why this happens is complex. Science suggests that there are genetic, biological and evolutionary factors that contribute. Twin studies show that genetics control about 25 percent of left-handedness, and conditions in the womb can also contribute to left-handedness. Even with these leads, no one understands the root cause of why some people are left hand dominant.