About 10% of people are left-handed, and this has held true for millennia. What’s maintaining that delicate balance? Daniel Abrams and Mark Panaggio of Northwestern University created a mathematical model to answer that question.
It turns out that it’s the amount of cooperation and competition in societies that determines the degree of left-handedness. In a culture that is entirely cooperative, no competition at all, being left-handed would be a definite disadvantage for both the individual and the tribe. The left-handed person can’t use the same tools as everyone else or can’t use them as well, leading to slower overall work or the need to create specialty items just for him.
On the other hand, in a highly competitive society, unusually-handed people would have an edge. For example, in a world where the majority of people are right-handed, and thus are used to fighting other right-handed people, left-handed combatants are more difficult to defeat. Lefties should outcompete righties until the lefties stopped being the minority, then the advantage should shift. Thus, highly competitive groups should have a 50-50 ratio of right to left-handedness.
So, how well does this model fit the real world? As I mentioned, in our relatively cooperative society, left-handers have made up roughly 10% of the population for the past 5,000 years. However, in the highly competitive world of sports, that number is closer to 50%. In fact, more than 50% of the top baseball players are lefties.
Abrams and Panaggio claim that they can use their model to predict the percentage of southpaws in any group, even non-human groups that display handedness like parrots. If their model is true, it suggests that human societies are much more cooperative than people give them credit for.