Genetic Traits Right Left Handedness

For thousands of years, people have wondered why some people have a preference for using one hand over the other. The majority of people are right handed, and in most cultures, there is a preference for right-handedness. This bias can be seen in language and other traditions. For example, to shake with the left hand is consider impolite in many cultures, and the word “sinister” is derived from the Latin word “sinestra,” which originally means “left.”

The factors that influence whether a person is right or left handed are complex. Genetics play a role in determining “handedness,” but environmental factors can also play a role. This article explains how these factors can intermix to cause a person to be right or left handed.

About Right or Left Handedness

About 90 percent of people are right handed, and humans are the only animals that show a significant bias toward using one hand over the other. Many people wonder why they are right or left handed. Though the factors that influence handedness are not completely understood, there is growing evidence that genetics may play a role.

However, while the genetics of some traits (like eye color) are relatively easy to understand, the genetics of being right or left handed are more complicated. You might assume that if two left handed people had a baby, that their child would also be left handed. But this is not always the case. In fact, the child of two left-handed parents has only a 40 percent chance of also being left handed. This is because hand preference is influenced by both genetics and environment.

Biology of Right or Left Handedness

Over the years, people have gained a better understanding of the role of brain functions in hand preference. The human brain is divided into two halves, or hemispheres. This is known as “lateralization.” In right handed people, the left side of the brain controls speech and language. In left handed people, the right side of the brain controls these functions. Lateralization also influences hand preference.

Genetics of Right or Left Handedness

Studies have generally shown that handedness is a weakly inherited genetic trait. However, in August of 2007, a group of researchers at Oxford University discovered a gene, LRRTM1, that appeared to affect whether a person would be right or left handed. The scientists also found that possessing this gene led to an increased risk of schizophrenia. This was the first time that scientists had positively identified a gene that affected human handedness.

However, it is likely a combination of biology and environmental factors that cause people to favor one of their hands over another. Studies of identical twins support this theory. If handedness were a completely inherited trait, identical twins would always share the same handedness. However, when one twin is left handed, the other twin is also left handed only three-quarters of the time. Some scientists think factors such as birth order and the age of the mother may also play a role in developing a particular handedness. Many cultures also have a bias against left-handedness, which may be part of the reason for high rates of right handedness.

Frequently Asked Questions about Right or Left Handedness

Q: Is there a gene for handedness?

A: In 2007, researchers at Oxford University discovered a gene that seems to increase the odds of being left handed.

Q: How common is left handedness?

A: About 10 percent of people are left handed.

Q: Are left-handed people at greater risk for any diseases?

A: Left-handed people may be at greater risk for conditions such as alcoholism, schizophrenia, Crohns disease, breast cancer and dyslexia.

Recent News on Right or Left Handedness

In 2005, Dutch researchers found that left-handed women were at a greater risk of developing breast cancer than their right handed counterparts. Yet another study in 2009 revealed that twins and triplets had a slightly increased likelihood of being left handed when compared to individuals that were not born multiples. Research regarding hand preference is delving into many other areas of study, and the findings thus far are astounding. As technology continues evolving, so will research methods, which may lead to even more discoveries regarding the genetics of right or left handedness.


Onion, A. (2005). The left-handed advantage. Retrieved June 28, 2009 from the ABC Web site: