Why Are Most People Right-handed?

An evolutionary balance between cooperation and competition decides the ratio of the right- to left-handed

For much of our observed history, the ratio of right-handed to left-handed people has remained constant at 90:10. This consistency begs an explanation. After all, why should the ratio not be 50:50?

Researchers at Northwestern University have developed a mathematical model to deal with this very question, and their answer suggests that the low percentage of lefties is a result of the balance between cooperation and competition in human evolution. They have used real-world data from competitive sports to confirm some of their claims published in The Journal of Royal Society Interface.

While the initial imbalance from a 50:50 ratio could be a matter of chance, the need to cooperate tilts the ratio in one direction. “The more social the animal—where cooperation is highly valued—the more the general population will trend toward one side,” said lead author Daniel M Abrams, “The most important factor for an efficient society is a high degree of cooperation. In humans, this has resulted in a right-handed majority.”

According to a university news release, ‘If societies were entirely cooperative everyone would be same-handed, Abrams said. But if competition were more important, one could expect the population to be 50-50. The new model can predict accurately the percentage of left-handers in a group—humans, parrots, baseball players, golfers—based on the degrees of cooperation and competition in the social interaction.’

‘Cooperation favours same-handedness—for sharing the same tools, for example. Physical competition, on the other hand, favours the unusual. In a fight, a left-hander in a right-handed world would have an advantage… The model accurately predicted the number of elite left-handed athletes in baseball, boxing, hockey, fencing and table tennis—more than 50 per cent among top baseball players and well above 10 per cent (the general population rate) for the other sports. On the other hand, the number of successful left-handed PGA golfers (the one case which is more akin to sharing of tools because of the handedness of the clubs) is very low, only 4 per cent.’

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