Left, right, or ambidextrous: What determines hand preference?

When you pick up your phone to read the daily science news, do you use your right hand or your left hand? Or do you use both hands equally? Scientists have begun to unravel the mystery of handedness.

The preference for using one hand to write and perform major tasks has fascinated humans for centuries. Stigmatized as evil or even unnatural, left-handed individuals have experienced their share of discrimination over the course of history.

In today's modern society, being left-handed is less of a big deal, and the rate of left-handed preference has steadily risen over the past century.

Many well-known individuals belong to the group of around 10 percent of the population that is left-handed, with Leonardo Da Vinci, Albert Einstein, Marie Curie, and Barack Obama among them.

But what can science tell us about how hand preference is determined?

Understanding handedness

Why is it important to understand hand preference? Scientists believe that this knowledge will contribute to a greater understanding of how the body assigns certain tasks to particular body regions.

Although from the outside our bodies look as though they might be symmetrical, once we get below the skin, all sense of symmetry is lost.

Scientists call this lateralization, which refers to the structural or functional differences between the right- and left-hand sides of our body.

In the brain, this is certainly evident. Many functions of the brain - such as language, memory, attention, emotional processing, and face perception - are specialized on one side of the brain.

Handedness has long been linked to language lateralization. In the majority of right-handed individuals, language dominance is on the left side of the brain.

But while common myth may have us believe that in left-handed individuals the sides are switched, only a quarter show language dominance on the right side of the brain.

Today, there is a broader understanding of hand preference, and many scientists believe that handedness is more of a continuous spectrum, rather than being defined by absolutes.

Over time, two new categories have joined the traditional lefties and righties. "Mixed-handed" individuals have a preference for a particular hand for certain tasks, whereas "ambidextrous" people, thought to be exceptionally rare, can perform tasks equally well with both hands.

The big question that remains is whether our genes or our environment determine handedness.

Single gene theory or epigenetic regulation?

Initially, several theories postulated that a single gene was responsible for hand preference. The combination of both sets of this gene - inherited from our parents - would determine handedness.

While these theories sound simple and convincing, there is no genetic evidence to date to back them up. Instead, research shows that several genes contribute around 25 percent toward handedness, and the rest is down to other factors.

But what could these other factors be? Are they environmental factors, such as upbringing or cultural influences, or is a more complex biological system responsible for the major factor in determining hand preference?

One study suggested that individuals who were breast-fed for a minimum period of 6 weeks were less likely to be left-handed. Meanwhile, another recent study proposed that much of the influence over hand choice is actually down to epigenetics, or gene regulation, which, in some cases, can be inherited.

Although there is still a lot of conflicting evidence, technological advances in genetic analysis mean that scientists are steadily homing in on the mystery of hand preference.