Handedness

Most people have a favorite hand.

They use it for tasks like writing. This hand is often faster and stronger. Most people use their right hand. About 90% of people are right-handed.

Some people use their left hand. This is less common. It happens in about 10% of people. Some people can use both hands well. Being left-handed can even help in sports. It is a very interesting way to work.

Most people have a favorite hand to use. This is called handedness. We call the hand you use most your dominant hand. This hand is often faster or stronger. The other hand is the non-dominant hand.

About 90% of people are right-handed. Only about 10% of people are left-handed. Some people are ambidextrous, which means they can use both hands equally well. This is very rare. Other people have mixed-handedness. This means they switch hands depending on the task.

Why does this happen? It is a mix of many things. Scientists think genes and the environment both play a part. This mix is called epigenetics. Some people think it relates to how the brain is built. In most people, the left side of the brain controls speech. Since the left side also controls the right hand, most people are right-handed.

Handedness can even help in sports. Left-handed people often do well in boxing or tennis. This is because opponents are used to right-handed players.

Most people have a favorite hand for tasks like writing or throwing. This is called handedness. We call the hand used most often the dominant hand. This hand is often stronger or faster than the other. The other hand is the non-dominant hand.

Some people are ambidextrous, meaning they use both hands equally well. This is very rare and only happens in about 1% of people. Other people have mixed-handedness, or cross-dominance. These people switch hands depending on the job they are doing.

Scientists study why we prefer one hand over the other. They use tools like the Edinburgh Handedness Inventory to measure this. Handedness is likely an epigenetic marker. This means it comes from a mix of genes and the environment. Research shows that genetics explain about 24% of handedness. The rest, about 75%, comes from environmental factors. Some studies suggest that prenatal hormone exposure might also play a role. For example, exposure to certain medications in the womb was linked to left-handedness.

Many people believe handedness is linked to how the brain is built. The brain has two sides called hemispheres. In most people, the left hemisphere controls speech. Because speech is a complex task, the brain may use that same side for fine motor skills. Since the left side of the brain controls the right hand, most people are right-handed.

However, about 30% of left-handers have a different brain organization. They might use the right hemisphere for language instead.

We can see handedness in history and in nature. Handedness is found in many animals like birds, reptiles, and mammals. Even Neanderthals showed a bias toward using their right hand. In a 1975 study of 7,688 children in the US, 9.6% were left-handed. Most people, about 90%, are right-handed. Handedness even shows up in ancient art. At the Cueva de las Manos in Argentina, many stenciled hands are left hands.

Being left-handed can offer unique advantages in the world. Many tools are made for right-handed people, which can be a hard job for others. However, left-handers often do well in sports like tennis, boxing, and fencing. This is because opponents are used to facing right-handed people.

Some researchers also look at how handedness links to talent. For instance, about 20% of Mensa members are left-handed. This is double the amount found in the general population.

Handedness refers to an individual's preference for using one hand over the other. This preferred hand is known as the dominant hand. It is typically stronger, faster, or more dextrous than the non-dominant hand.

While most people favor one side, some people exhibit different patterns. Ambidexterity describes having equal ability in both hands, though natural ambidexterity is rare, occurring in only about 1% of the population. Mixed-handedness, or cross-dominance, occurs when a person changes their preferred hand depending on the specific task. This trait is associated with childhood brain development and is about as common as left-handedness.

Scientists categorize handedness into several distinct types based on how people use their hands. Right-handedness is the most common type, used by approximately 90% of the population. Left-handedness is less common, affecting about 10% of people. As mentioned, natural ambidexterity is a very small group. Mixed-handedness is another category where hand preference shifts between tasks. Researchers measure these preferences through behavioral performance tests or questionnaires. The Edinburgh Handedness Inventory has been used since 1971 to track these patterns. Newer tools like the Flinders Handedness Survey (FLANDERS) have also been developed to study these differences.

Understanding why handedness occurs involves looking at complex biological causes. Most research suggests left-handedness is an epigenetic marker. This means it results from a combination of genetics, biology, and the environment. Studies show that genetic factors explain about 24% of the variance in handedness. Environmental factors account for the remaining 75%. For example, exposure to the synthetic estrogen-based medication diethylstilbestrol in the womb has been linked to higher rates of left-handedness. Some research also suggests a weak association between ultrasound screening during pregnancy and left-handedness.

Genetics play a major role through a process called polygenic inheritance. This means handedness is not controlled by a single gene. Instead, at least 40 different genetic locations, or loci, are estimated to contribute to the trait. Research by Brandler and colleagues suggests that genes determining left-right asymmetry in the body also influence handedness. These same mechanisms, such as nodal signaling and ciliogenesis, may help determine brain asymmetry. This brain asymmetry then reflects how motor functions are controlled. Essentially, the way our bodies are built on the left and right sides is tied to how our brains are organized.

One popular theory involves the division of labor between the two brain hemispheres. In most humans, the left hemisphere of the brain is responsible for controlling speech. Because speech is a highly complex motor task, the brain may use the same hemisphere for fine motor skills. Since the left hemisphere controls the right hand, most people become right-handed. However, the organization in left-handed people is more varied. While most left-handers still use their left hemisphere for language, about 30% do not. These individuals may have reversed organization or a more ambiguous bilateral organization where both sides share tasks.

Handedness is not unique to modern humans. It has been observed in dozens of non-human vertebrates, including amphibians, reptiles, birds, and mammals. While data regarding fish is still debated, the trait is clearly present in many species. In some non-human primates, individuals are split almost equally between right and left preferences. This differs from humans, who show a strong right-biased preference. Even Neanderthals appear to have had a right-handedness bias. We can see historical evidence of this in ancient art, such as the stenciled hands at the Cueva de las Manos in Argentina.

Handedness can influence a person's experience in the world and their performance in certain activities. Because most tools and devices are designed for right-handed users, left-handed people may find them more difficult to use. However, left-handedness provides a distinct advantage in many sports. Left-handers are over-represented in baseball, tennis, fencing, cricket, boxing, and mixed martial arts. This is because opponents are more accustomed to competing against right-handed players.

This unexpected advantage allows left-handers to thrive in high-speed, competitive environments.

There is also a complex relationship between handedness and cognitive traits. Some researchers, such as Chris McManus, suggest that left-handers may have brain structures that allow for more diverse processing of language, space, and emotion. While studies show the difference in average IQ between right and left-handers is negligible—only about 1.5 points—some interesting patterns emerge. For example, left-handers are over-represented in high IQ societies like Mensa, making up about 20% of its members. Conversely, left-handers are also more likely to be represented among those with intellectual disabilities. These findings show that handedness is a deeply connected part of human biology and cognitive diversity.