If you know an older left-handed person, chances are they had to learn to write or eat with their right hand. In many parts of the world, it's still common practice to force children to use their "proper" hand. The word for "right" often also means "correct" or "good" in many languages, not just in English. But if being left-handed is so wrong, why does it happen in the first place?
Today, about 10% of the world's population are left-handed. Archaeological evidence shows that this ratio has persisted for at least 500,000 years. About 10% of ancient human remains show differences in arm length and bone density associated with left-handedness, and some ancient tools and artifacts indicate left-hand use.
Despite common misconceptions, handedness is not a choice. It can be predicted before birth based on the fetus' position in the womb. So, if handedness is inborn, does that mean it's genetic? Well, yes and no. Identical twins, who share the same genes, can have different dominant hands, occurring as often as with any other sibling pair. However, the chances of being right or left-handed are influenced by the handedness of your parents in surprisingly consistent ratios. For instance, if your father is left-handed but your mother is right-handed, you have a 17% chance of being left-handed. Two right-handed parents have a left-handed child only 10% of the time. This suggests that while handedness is somewhat genetic, it also involves other factors.
Evolution has maintained this small proportion of left-handers over millennia. Several theories have attempted to explain why handedness exists and why most people are right-handed. A recent mathematical model suggests that the actual ratio reflects a balance between competitive and cooperative pressures in human evolution.
The benefits of being left-handed are clearest in activities involving an opponent, like combat or competitive sports. For example, about 50% of top hitters in baseball are left-handed. This advantage arises because left-handers, being a minority, are less predictable to right-handed opponents who are more accustomed to facing other righties. This concept, known as the "fighting hypothesis," is an example of negative frequency-dependent selection. However, evolution suggests that groups with a relative advantage tend to grow until that advantage diminishes. If human evolution were driven purely by competition, 50% of the population would be left-handed.
But cooperation has also shaped human evolution, pushing handedness distribution in the opposite direction. In sports like golf, where performance doesn't depend on an opponent, only 4% of top players are left-handed. This reflects the wider phenomenon of tool sharing. Many important instruments that have shaped society were designed for the right-handed majority. Left-handers, being less adept at using these tools and experiencing higher accident rates, would be less successful in a purely cooperative world and eventually disappear from the population.
Thus, the persistence of lefties as a small but stable minority results from a balance of competitive and cooperative effects. This model accurately predicts the distribution of left-handed people in the general population and aligns with data from various sports. Interestingly, the numbers can also provide insights into different populations. For instance, cooperative animals show a skewed distribution of pawedness, and competitive hunter-gatherer societies have a slightly higher percentage of lefties. These patterns suggest that some puzzles of early human evolution may already be in our hands.
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