What Causes Left Handedness: Unraveling the Mystery

Left handedness is a curious phenomenon that has puzzled experts for a long time. While it may seem like a minor detail, being left-handed can significantly impact the way someone interacts with the world. For example, left-handed people may struggle with everyday objects designed for right-handed individuals, such as can openers or scissors. Despite being present in only around 10% of the population, left-handedness has fascinated scientists for centuries.

This article will explore the mystery of what causes left-handedness, including genetic factors, environmental influences, and the advantages and disadvantages of being left-handed.

What is left-handedness?

Left-handedness refers to people who predominantly use their left hand for tasks such as writing, drawing, and throwing. While most people are right-handed, approximately 10% of the world’s population is left-handed, and studies show that left-handedness occurs more frequently in males than females. Left-handedness can be observed in both humans and animals, but the reason for the prevalence of right-handedness in most species is not yet understood.

The role of genetics

Scientists have long been interested in whether left-handedness is inherited or if it is caused by environmental factors. According to several studies, genetics seems to play a role in determining handedness.

Research suggests that left-handedness may be linked to genetics, specifically the presence of one or more genes that influence brain development. Studies have shown that people with left-handed relatives are more likely to be left-handed themselves, with approximately 25% of left-handed individuals having left-handed parents or siblings.

However, while science continues to explore the genetic basis of left-handedness, the specific genes involved are still not entirely clear.

The handedness gene

One of the genes that have been closely examined in association with handedness is called LRRTM1. This gene is believed to be involved in brain development and is usually found in higher concentrations in the brains of left-handed individuals. As a result, some scientists believe that LRRTM1 may be the so-called “handedness gene.”

Studies have shown that people who inherit a specific variation of LRRTM1 from both parents are more likely to be left-handed. However, even with this gene variation, there is no guarantee that an individual will be left-handed. Other factors, including environmental influences on brain development, can also play a role.

The brain and handedness

One of the main reasons why scientists believe that genetics plays a role in handedness is that the brain operates differently depending on whether an individual is left-handed or right-handed.

Research has shown that the brains of left-handed individuals are structurally different from those of right-handed individuals. For example, the right hemisphere of a left-handed person’s brain is usually more dominant than the left hemisphere, and the structure of the brain tissue in the two hemispheres is different.

The left hemisphere of the brain is typically responsible for language, speech, and reasoning, while the right hemisphere is more involved in spatial awareness and emotional processing. In left-handed people, these functions may be distributed more evenly between the two hemispheres, resulting in different cognitive and social abilities than right-handed people.

Environmental factors

While genetics undoubtedly plays a role in handedness, environmental factors can also influence the development of handedness during fetal development or early childhood.

The fetal environment

Several studies have suggested that the environment in the womb can influence handedness. For example, one theory is that the position of the fetus in the uterus can impact brain development and result in a preference for using either the left or right hand.

Research also shows that prenatal exposure to hormones, particularly testosterone, can influence handedness. High levels of testosterone exposure in utero can lead to a higher likelihood of left-handedness, although the mechanism behind this is currently not entirely understood.

Early childhood experiences

Another environmental factor that may influence handedness is the motor experiences of an individual during their early years. Research has shown that motor experiences, such as the consistency of handedness in response to various tasks, can shape the development of laterality in an individual. If a child consistently uses their left hand for certain tasks, their brain may become more inclined towards left-handedness. Similarly, when children are explicitly trained in right-hand skills, they might preferentially develop right-handedness.

The advantages and disadvantages of being left-handed

Left-handedness is often associated with certain benefits and drawbacks, both of which can influence an individual’s cognitive and social abilities.

Advantages of being left-handed

  • Enhanced problem-solving abilities: Studies have suggested that left-handed people may have an advantage in certain problem-solving tasks. This could be because they use both sides of their brain more efficiently or because they are better at seeing things from a unique perspective.
  • Artistic abilities: Many left-handed people are particularly talented in art and music, possibly due to the cognitive and perceptual differences of their brains.
  • Athleticism: Left-handed athletes may have an advantage in certain sports, such as baseball or tennis, where left-handedness can be advantageous due to their opponents’ increased familiarity with right-handed players.

Disadvantages of being left-handed

  • Inconvenience: Everyday objects and tools such as scissors, can openers, and computer mice are often designed with right-handed people in mind, making tasks more inconvenient for left-handed individuals.
  • Acing difficulties: In some circumstances, left-handed writing may be difficult to read due to the slope and direction of the writer’s hand as they write.
  • Cognitive differences: While left-handers often exhibit faster cognitive processing than right-handers, they also tend to have a weak short-term memory and are more prone to develop dyslexia.

Common questions about left-handedness

  • Is left-handedness genetic?
  • What causes left-handedness?
  • Can left-handedness be increased or encouraged?
  • What are the benefits of being left-handed?
  • What are the disadvantages of being left-handed?
  • Do left-handed people have different brain structures?
  • Why are most people right-handed?


Left-handedness has been the subject of fascination and mystery for a long time. While scientists have uncovered some of the genetic and environmental factors that influence handedness, many questions remain unanswered. Understanding the causes of left-handedness can help us appreciate the diversity of human traits while providing valuable insights into brain development and function.


1. McManus, I. C. (2019). Left-handedness: From “sinister” to evolved trait. Biological Reviews, 94(1), 367-379.

2. Papadatou-Pastou, M., & Tomprou, D. M. (2014). On the mental benefits of being left-handed: Differential patterns of cognitive advantage and disadvantage in left-handed and right-handed individuals. Frontiers in psychology, 5, 612.

3. Sommer, I. E., Aleman, A., Ramsey, N. F., & Bouma, A. (2001). Handedness, language lateralisation and anatomical asymmetry in schizophrenia: meta-analysis. The British Journal of Psychiatry, 178, 344-351.

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