Specifically, lefties have an advantage in sports that involve aiming something toward an opponent—think baseball, tennis, fencing, and boxing. That can be explained almost entirely by one simple fact: lefties are rare. In line with the population at large, 90 percent of kids who start playing baseball are right-handed. So when a player faces off against that rare lefty pitcher or lefty batter, it throws them off their game. That gives left-handed players a leg up on the competition, and helps them rise through the professional ranks faster than their right-handed counterparts.

That's not just a theory. Research shows that in comparison to the 10 percent of people who are left-handed in the general population, southpaws make up one-third of Major League Baseball players, 20 percent of the top-ranked boxers, and 20–25 percent of the top-ranked fencers. The same isn't true for sports where lefties wouldn't have an edge, like golf and American football.

This advantage extends beyond fun and games into real-world survival—after all, sports are just an organized form of war when you think about it. In 2005, French researchers Charlotte Faurie and Michel Raymond published a study demonstrating that in societies that tend to be "the most violent and warlike," the proportion of left-handed people can be as high as 27 percent, compared to only 3 percent in the most peaceful societies.

In fact, researchers think that this tendency for conflict to favor left-handedness is evidence for why so many of us are right-handed: humans value cooperation. In 2012, researchers Daniel Abrams and Mark Panaggio published a study in the Journal of the Royal Society Interface that found that the more social a species is, the more the individuals will favor one side or the other. That's important for cooperation, since it makes it easier to share tools, food, and other essentials. But as we reported earlier, surprise is important for competition, which is why someone who favors a different side has an advantage. That's why even though 30 percent of elite baseball players throw the ball with their left hand, they'll still reach with their right to shake yours.