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“There’s something I ought to tell you. I’m not left-handed either.” – Westley, The Princess Bride

Throughout history, left-handedness has both fascinated and frightened people. Maybe it is because only about 15 percent of the population is left-handed. Or maybe it is because the reasons for left-handedness remain somewhat of a mystery.

What makes a person left- or right-handed? It seems we can find the answer in our genes, at least partially. Most researchers in the field agree that left- or right-handedness is most likely produced by genetic influences. We inherit our genes from our parents, and the genes that are turned on determine our characteristics. The specific reasons behind these genetic differences are still hotly debated, but many studies seem to point to natural selection as a probable cause.

The human brain is divided into the right and left hemispheres, with nerve fibers connecting the two. Different parts of each half of the brain control different functions of the body. Many evolutionary biologists argue that evolution produced a majority of people who controlled language with their left brain, which also controls the right side of the body, including the right hand. As written language developed, people with genes toward right-handedness had a genetic advantage and passed those genes down to their children. But the question remains: Why are some people left-handed when natural selection seems to be evolutionarily “against” left-handedness?

Scientists have discovered that handedness is influenced by not just one, but a group of genes, and that these genes can be influenced by external and societal pressures. For example, if a person expresses the genes for left-handedness, they may be taught to write with their right hand. In the same way, a person who writes with their right hand can be taught to use their left hand to throw or shoot a ball for a competitive advantage.

Although it may be more difficult to find a pair of scissors or spiral notebook that are easy to use, left-handedness has its advantages. Left-handers have been shown to have greater coordination, and left-handedness has been linked to creativity, especially in men. This may be due to the connection with the right brain, which is the creative hemisphere. Many lefties excel in sports such as tennis and fencing, possibly because there are fewer left-handed opponents.

While research continues into what makes left-handed people unique, we can celebrate our left-handed friends now in honor of Lefthanders Day on August 13.

Audrey A. Vasauskas, PhD, is an associate professor of physiology at the Alabama College of Osteopathic Medicine. She is a former volunteer editor for the I Spy Physiology blog.