The real reason some people are left-handed

It sucks being a lefty in a right-handed world. And we're not just talking about having your mug face the wrong way, which is annoying in and of itself — what's the point in having a mug that says something clever when no one can see what it says? We're also talking about the elbow wars lefties and righties have at a crowded dinner table, spiral notebooks, desks that favor righties, and of course, computer mice. 

Lefties weren't always left out in the cold. Ranker says the ancient Celts celebrated left-handedness because it was an advantage in combat. The Kerr family trained their sons and the guards to hold their swords and axes in their left hands because it was supposed to give the clan an advantage in battle. The ancient Romans also saw the left side as auspicious and noted that if a bird flew into a templum (a sacred space in the sky) from the left, that was a good sign, but if it flew in from the right, it meant the gods disapproved. 

Why left-handedness started to be viewed in a different light

Because only a small fraction of the world's population is left-handed, right-handedness became a sign of dominance, strength, and virtue. Ranker says many religions, including Christianity, Hinduism, and Jewish Kabbalah have all made the same association that right was, well... right. History is full of stories about how left-handed people were persecuted, and Owlication has a few. For example, during the Middle Ages, being left-handed meant being persecuted for playing on the Devil's team. 

It didn't end there, though. Spanish Inquisitors considered being left-handed as evidence that a person was involved in witchcraft, and as a result, he or she was also against the Catholic church. Even doctors claimed lefties either had the "mark of criminality" (Cesare Lambroso) or favored their left hand "due to perversity and the result of emotional negativism" (Abram Blau). Fun fact: did you know the Latin roots for the words "right" and "left" are dexter (which means dexterous, meaning skilled, nimble) and sinister (which means evil, dark, wrong)?

Your spinal cord determines which hand you use

Scientists used to think that the preference for being left- or right-handed was dictated by genetics and that differences between the left and right hemispheres of the brain determined whether someone was left- or right-handed (via Business Insider). But in a study published by eLife, researchers say fetuses already pick a favorite thumb before the part of their brains which control movement are linked to the spinal cord, which means that long before the brain starts controlling the body, the fetus already has a preference for handedness. 

As a result, Business Insider says the spinal cord's asymmetrical nature could be affected by what scientists call "gene-expression differences" instead of by the genes themselves. While the study may finally explain where left-handedness comes from, it leaves one important factor unsolved: why only about 10 percent of the population is left-handed.