Nine out of every ten humans are right-handed, an imbalance that researchers for decades have attempted to explain, without definitive success.
One of the ideas considered is the fighting hypothesis, which suggests that left-handedness provides an advantage in combat, albeit with an overall hit to physical health that keeps lefties rare in the population. Indeed, males — who historically have competed most strongly for resources and mates — are left-handed at slightly higher rates than females. Moreover, studies suggest that lefties tend to outperform right-handed people in fighting sports as well as in sports that require hand-eye coordination like tennis, baseball, and volleyball. This is likely because players are unaccustomed to competing against lefties as they are rarer.
So why do right-handed humans have a fighting advantage? According to the researchers, it has to do with the position of the heart and the notion that humans did most of their fighting with handheld, pointy weapons like wooden spears for much of our species’ existence.
About three-quarters of the heart is situated in the left hemithorax, making the left side of the chest a susceptible target for a mortal blow. The researchers note that when humans battle with stabbing weapons, the hand utilized to hold the weapon determines which area of the chest is exposed to an opponent.