In a room of 25 people, you’d find that, on average, only two people in that room are likely to be left-handers. Handedness, also called hand preference, is the preference for one hand over the other for everyday tasks like eating or writing. There are three types of handedness – Left-handedness, right-handedness, and mixed-handedness (preferring to use either hand for different tasks). Data collection studies say that about 8% of the world’s population is left-handed, and about 1% is mixed-handed. Handedness may have a biological origin and result from how the right and left hemispheres of the brain coordinate and function. This article will explore the genetics behind handedness and why there are so many more right-handers than left-handers.
What Causes Some People To Be Left-handed?
The left brain hemisphere controls the right side of the body and vice versa.
Hand motor control is typically under the control of the left hemisphere.
That’s why most people are right-handed by nature.
A few theories have been proposed to explain the preference of one’s left hand.
Genetic mechanisms or prenatal trauma could cause asymmetrical brain development.
Consequently, the right hemisphere gains control of motor function, leading to left-handedness.
Learn More About How Genetics Can Influence Everyday Traits
Is Handedness Genetic?
According to experts, conditions like prenatal trauma may play a small role in changing hand dominance.
Sometimes, postnatal (societal) pressure could influence a left-handed child to start using their right hand.
However, genetics remains a significant cause.
Recent studies have found up to 40 genes that could lead to handedness through common genetic influence.
Scientists have only identified a few of these genes.
One gene of interest is NME7 (NME/NM23 Family Member 7).
This gene regulates the position of organs along the left-right axis of the body.
It likely plays a role in influencing body symmetry and an individual’s tendency to prefer their left hand.
Why Are There Fewer Left-handed People Than Right-Handed?
It’s easiest to understand this through an example.
We know that every gene has two alleles or versions.
Let gene X be the gene associated with handedness.
It has two alleles, a and b.
“a” is dominant, the more common allele in the human population that influences right-handedness.
“b” is a chance, rarer allele.
The b allele imparts a 50% chance that a child prefers their left hand.
It doesn’t guarantee that a child will be born left-handed
Since the child receives one allele from each parent, the possible combinations are aa, ab, and bb.
- Children with the aa genotypes will be right-handed.
- Children with the ab genotypes will mostly be right-handed.
- Children with the bb genotypes will likely be left-handed. However, due to the chance nature of the b allele, children could also be right-handed.
Out of these possibilities, only a particular incidence of allele makeup leads to left-handedness.
That’s why right-handers are more prevalent than left-handers in a given population.
Genetic Differences Associated With Left-handedness
Due to their genetic differences, a number of left-handed people could be at a slightly higher risk of certain health conditions.
However, a majority of left-handers have an advantage against conditions like ulcers, stroke recovery, and arthritis.
Additionally, since the brain's right hemisphere is responsible for creativity, many A-list celebrities and musicians are left-handed.
Some famous left-handers include former President Obama, actress Angelina Jolie, musician Lady Gaga, and entrepreneur Bill Gates.
These gene changes also give left-handers an advantage in sports. For instance, nearly 30% of the top pitchers in baseball are left-handed.
Is Left-handedness Related to Health Status?
Left-handed people may be at a greater risk of certain health conditions.
Left-Handedness And Cerebral Palsy
An open-access 2012 study analyzed handedness in 111 children with spastic diplegic cerebral palsy and 444 without the condition.
About 40% of children with cerebral palsy were left-handed, while only 2% of study subjects without the condition were left-handed people.
The study suggests that left-handedness may be frequently seen in children with cerebral palsy.
Left-Handedness And Schizophrenia
A 2015 study conducted on a group of people diagnosed with schizophrenia showed a clear majority of left-handedness among patients.
There was no other gender-based or behavioral link to the occurrence of schizophrenia.
Thus, the study indicated that psychiatric disorders like schizophrenia and left-handedness could be related.
Left-Handedness And Breast Cancer
In 2016, a study reported that the median age of breast cancer diagnosis in a group was higher for right-handed people.
Generally, left-handed people were diagnosed earlier with similar severity and disease characteristics.
Thus, the study recommended that left-handed people be screened for breast cancer earlier.
Left Handedness And Post Traumatic Stress Disorder (PTSD)
A 2007 study screened 596 individuals for signs of PTSD; out of these, 51 individuals had a positive diagnosis.
Most of these people were left-handed, and the study also found that left-handed individuals had more severe symptoms of PTSD than right and mixed-handers.
In 2023, researchers conducted a meta-analysis for handedness on 3000 individuals.
The results clearly showed a higher incidence of non-right-handedness and mixed-handedness in PTSD patients.
Left Handedness And Birth Complications
Some cases of left-handedness could be because of physical stress or trauma the fetus goes through while in early development in the uterus.
The brain’s left hemisphere is more sensitive and prone to damage than the right.
If the left hemisphere is damaged, cerebral dominance switches to the right side, and the child is born left-handed.
These experts also mention that this could be why congenital disabilities are common in left-handed babies.
Recommended for you: Can Your Dominant Hand Affect Your Grip Strength?
Summary: Is Handedness Genetic?
- Handedness is primarily genetic.
- More than 40 genes play a role in influencing handedness
- It can also be affected by prenatal or postnatal trauma
- This deviated brain pattern could put left-handers at increased risk of conditions like cerebral palsy, schizophrenia, PTSD, birth complications, and breast cancer.
- However, left-handers are at a lower risk for conditions like ulcers and arthritis and recover from strokes faster.
- Left-handers’ brains’ right hemispheres control motor function as well as creativity, which is why many celebrities are left-handed.
Frequently Asked Questions
Can Two Right-handed Parents Have A Left-handed Child?
Two right-handed parents could have a left-handed child if they are both carriers of the left-handed gene without expressing it themselves. They could pass on one allele each to their child.
At What Age Can You Tell Handedness?
Within a year, at about 10-11 months, infants develop a preference for one hand over the other. This preference stabilizes over the next year or so.
Do Left And Right-handers Have Different IQ Levels?
A 2019 study studied this and reported no significant difference in the IQ of left- and right-handed individuals in a population.
References
- https://medlineplus.gov/genetics/understanding/traits/handedness/
- https://www.pnas.org/doi/10.1073/pnas.2113095118
- https://www.scientificamerican.com/article/what-causes-some-people-t/
- https://pubmed.ncbi.nlm.nih.gov/1839378/
- https://edition.cnn.com/2019/09/05/health/uk-left-handed-genes-brain-structure-scn-scli-intl
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3345498/
- https://www.healthline.com/health/left-handers-and-health-risk
- https://www.webmd.com/brain/ss/slideshow-left-handed-vs-right
- https://www.sciencedirect.com/science/article/abs/pii/S0149763417300210
