Look around any classroom, office, or family reunion and you'll usually spot a few people writing with their left hands. They're in the minority, and they always have been. So what makes someone a lefty in the first place?
The short answer is that it's a mix of genes and other factors, and scientists haven't pinned down the full recipe. About 10 percent of people are left-handed. Research suggests handedness is shaped by many genes working together, along with influences from the environment and development before birth. There's no single “lefty gene.”
It Runs in Families, Sort Of
Handedness does run in families, but not in a neat, predictable way. If both parents are left-handed, there's about a 26 percent chance their child will be left-handed too. That's higher than average, but it still means most children of two lefties end up right-handed.
A large twin study covering more than 25,000 families estimated that genes explain only about a quarter of the differences in handedness between people. The other three-quarters seem to come from non-genetic factors.
Scientists once hoped one gene would explain it all. Instead, newer studies suggest at least 40 different spots in our DNA play a part. Interestingly, some of them are genes that help set up the left and right sides of the body as it develops. A 2019 study found four clear genetic links to handedness, and three of them were in genes involved in brain development.
The Brain Connection
One popular theory focuses on the brain. In most people, the left side of the brain controls speech, and the left side of the brain also controls the right hand. The idea is that the same fine-control areas that handle speaking also handle the skilled hand, which would make most people right-handed.
It's a tidy theory, but it doesn't fully hold up. Most left-handed people also have speech controlled by the left side of the brain, just like right-handers. Only around 30 percent of lefties are wired differently, so the puzzle remains partly unsolved.
A Very Human Quirk
Plenty of animals have a favorite side, from birds to reptiles to mammals. But most monkeys and apes are split roughly evenly between left and right preferences. Humans stand out among primates for having such a strong lean toward the right.
That lean goes back a long way. Scratch marks on Neanderthal teeth suggest they also tended to be right-handed, much like us.
A Bad Rap, and a Secret Advantage
Lefties have often been treated unfairly. The English word “left” comes from an Anglo-Saxon word meaning “weak.” In Latin, the word for left, sinister, came to mean evil or unlucky, while the word for right, dexter, gave us “dexterity.” In many countries, left-handed children were made to write with their right hands. Those who switch hands can become skilled with the trained hand, especially if they learn young, but many still lean toward their original side.
Being different can pay off, though. Left-handed people are over-represented in sports like baseball, tennis, fencing, and boxing. Opponents are used to facing right-handers, so a lefty's angles can catch them off guard.
So if you're one of the lefties, you're in good company: part of a steady one-in-ten slice of humanity with a long, colorful history. And if you've ever smudged ink across a page or wrestled with right-handed scissors, at least now you know it's not your fault.
