Why Do We Have Dominant Hands? Exploring the Theories of Handedness in Humans

Humans exhibit a unique trait of hand preference within the animal kingdom, having a dominant hand that they favor for daily tasks.

Secrets of Human Handedness

Handedness is believed to be determined at the earliest stage of human development. In a 2005 study entitled "Prenatal thumb sucking is related to postnatal handedness," researchers reported that a fetus shows a hand preference in the womb by sucking the thumb of one hand. This trait continues after they are born.

It was previously thought that a single gene controlled handedness in humans, but recent studies reveal that up to 40 genes contribute to this trait. Each of these genes has a weak effect, but they play a significant role in establishing hand preference. So far, the researchers have identified only a few of these genes.

Although there is no gene for being right-handed or left-handed, our DNA seems to play a role in handedness. In a separate study, experts from the University of Oxford investigated the DNA of almost 400,000 people in the U.K. They discovered that four regions of the genome are generally linked with left-handedness. Three of these regions are involved in brain structure and development.

Like other complex human traits, hand preference does not have a simple inheritance pattern. For instance, children of left-handed parents are more likely to be left-handers than children of right-handed parents. Still, the overall chance of being left-handed is relatively low, where most children of left-handed parents are right-handed.

Why are Most People Right-Handed?

Almost 85% to 90% of humans are right-handed, and there is no population where lefties are in the majority. Righties have dominated the human population for as far back as 500,000 years. According to Max Planck Institute for the Science of Human History senior scientist Natalie Uomini, Neanderthals were found to be strongly right-handed.

This trend makes humans a bit strange among the members of the animal kingdom. Several nonhuman species are individually handed, but the division between right-handedness and left-handedness is almost close to 50-50.

What could have caused our extreme bias toward right-handedness to evolve and persist? From an evolutionary point of view, if right-handedness evolved due to some advantage, we might expect lefties to disappear completely. Uomini also added that there are some disadvantages to being left-handed, like higher frequencies of work accidents.

The possible reason why left-handers have maintained a constant minority is explained in a leading theory called the fighting hypothesis. It suggests that in hand-to-hand combat, or those that involve weapons, being a minority left-hander has a surprise advantage because most people are used to fighting against right-handers. A study published in 2010 showed that lefty advantage can be observed in one-on-one sports such as fencing.

If this hypothesis is correct, it means that while left-handedness is significant enough to keep lefties in the minority, their advantage in combat at least gave them a fighting chance against possible extinction.