Why are some people left-handed? Cooperative and Competitive World

If you know an older left-handed person, chances are they had to learn to write or eat with their right hand. And in many parts of the world, it’s still a common practice to force children to use their “proper” hand. Even the word for right also means correct or good, not just in English, but many other languages, too. Left-handedness in humans has long fascinated scientists and society. If you know an older left-handed person, chances are they had to learn to write or eat with their right hand.

But if being left-handed is so wrong, then why does it happen in the first place?

Today 1/10 of the world’s population are left-handed. Archeological evidence shows this pattern for 500,000 years. About 10% of human remains show differences in arm length and bone density, and ancient tools reveal left-hand use.. Despite common belief, handedness isn’t a choice. It can be predicted before birth from the fetus’ position in the womb.

Genetics and Handedness

Identical twins share the same genes but can have different dominant hands. This happens as often as with any siblings.. Your parents’ handedness strongly influences your own, following surprisingly consistent ratios.. If your father was left-handed but your mother was right-handed, you have a 17% chance of being born left-handed, while two righties will have a left-handed child only 10% of the time. Handedness seems to be determined by a roll of the dice, but the odds are set by your genes.

Evolution Shaped Left-Handedness in Humans

All of this implies there’s a reason that evolution has produced this small proportion of lefties, and maintained it over the course of millenia. Several theories explain why handedness exists and why most people are right-handed. A recent model shows the ratio reflects a balance of competition and cooperation in evolution.

Competitive Advantage of Being Left-Handed

Left-handed players shine in opponent-based activities like combat or competitive sports. About 50% of top hitters in cricket or baseball are left-handed. Lefties hold a surprise advantage because most competitors train against right-handers. So when they face each other, the left-hander is better prepared while the righty may be thrown off.

The Fighting Hypothesis: Why Some Lefties Thrive

The fighting hypothesis suggests that fewer left-handers gain an advantage over right-handers, a case of negative frequency-dependent selection. But in evolution, once a group gains advantage, its numbers grow until the edge fades.. If humans only fought and competed, natural selection would favor lefties until they became common and lost their rarity.

So, in a purely competitive world, 50% of the population would be left-handed. But human evolution has been shaped by cooperation, as well as competition. And cooperative pressure pushes handedness distribution in the opposite direction.

Left-Handedness in Modern Society

In golf, where performance doesn’t depend on the opponent, only 4% of top players are left-handed, an example of the wider phenomenon of tool sharing. Just a young potentual golfers can more easily find a set of right-handed clubs, many of the important instruments that have shaped society were designed for the right-handed majority. Because lefties are worse at using these tools, and suffer from higher accident rates, they would be less successful in a purely cooperative world, eventually disappearing from the population.

So by correctly predicting the distribution of left-handed people in the general population, as well as matching data from various sports, the model indicates that the persistence of lefties as a small but stable minority reflects an equilibrium that comes from competitive and cooperative effects playing out simultaneously over time. And the most intriguing thing is what the numbers can tell us about various populations. From the skewed distribution of pawedness in a cooperative animals, to the slightly larger percentage of lefties in competitive hunter-gatherer societies, we may even find that the answers to some puzzles of early human evolution are already in our hands.

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