What Decides Handedness? Is It Genetics?

Have you ever pondered why some people are naturally inclined to use their left hand for tasks, while others default to their right hand?

This intriguing preference, known as handedness, raises several questions: Is left-handedness genetic? Are more people genetically predisposed to right-handedness? And what percentage of humans are left-handed?

In this article, we’ll uncover the roles of genetics, like the so-called left-handed gene, and environmental influences in determining our dominant hand.

Let’s dig in to find out whether being left-handed or right-handed is etched in our DNA, and how this trait reflects the on role of our genes and the world around us.

Quick Note:

Handedness, the preference for using one hand over the other, is a complex trait influenced by both genetics and environment. Key genes like PCSK6 and LRRTM1 are involved, affecting brain development and body symmetry, contributing to our preference for using the left or right hand.

While there isn’t a single ‘left-handed’ or ‘right-handed’ gene, the interplay of multiple genes, combined with environmental factors such as prenatal conditions and cultural practices, shapes our hand preference.

This trait also links to various brain functions and can be associated with certain neurodevelopmental conditions like dyslexia, autism, ADHD, and schizophrenia.

Understanding handedness offers insights into the complex interaction between our genetic makeup, brain development, and environmental influences.

For a detailed understanding of handedness and its broader implications, keep reading!

Historical and Cultural Views on Left and Right Handedness

Over the years, different places and cultures have had their own ideas about left-handed and right-handed people.

Left Hand vs. Right Hand: What People Used to Think

In some old cultures, being left-handed was seen as something really special. For example, in ancient Greece, lefties were thought to be really artsy and smart. They were linked to Athena, the goddess who was all about wisdom and art.

In China, if you were left-handed, people might think you’re a genius. It was something seen in emperors and smart folks.

Some Native American groups even thought left-handed people had healing powers, kind of like doctors or spiritual healers.

But not all places thought being left-handed was great.

In ancient Rome, the word for left also meant bad luck or even evil. In medieval Europe, lefties sometimes got accused of witchcraft, and that was really dangerous.

Even now, in some countries, if you’re left-handed, it can be seen as not clean or proper, especially when it comes to eating or saying hello.

A lot of kids in Africa, Asia, and Latin America are even made to use their right hand instead of their left because using the left is seen as rude.

The Struggles and Successes of Left-Handed People

All these beliefs have made life tough for lefties. They’ve faced being treated unfairly and have had to deal with a world mostly made for right-handed people.

Think about how most tools, computers, and even musical instruments are set up.

Despite these hurdles, left-handed people have done some amazing things. They’ve been creative and successful in all sorts of areas.

Some really famous and important people in history were left-handed, like the artist Leonardo da Vinci, the scientist Albert Einstein, Nobel Prize winner Marie Curie, leader Mahatma Gandhi, former U.S. President Barack Obama, and TV personality Oprah Winfrey.

So, while left-handedness might have been seen differently across times and places, left-handed people have shown they can do great things, no matter which hand they prefer.

Understanding Handedness

Let’s talk about what it means to be right-handed or left-handed, and figure out how many people are left-handed.

Handedness is all about which hand you usually use for things like writing or eating.

But not everyone sticks to just one hand. Some folks use different hands for different things, or might switch hands based on what they’re doing. These people are often called mixed-handed or ambidextrous.

So, handedness isn’t just “this or that;” it’s more like a sliding scale from very right-handed to very left-handed, with lots of mixed-handedness in the middle.

To measure handedness, there’s this test called the Edinburgh Handedness Inventory.

It’s a set of questions that asks which hand you use for 10 everyday actions.

You score it from -5 (always using the left hand) to +5 (always using the right hand). Add up your scores, and you can get anything from -50 (super left-handed) to +50 (super right-handed).

If you get a 0, it means you don’t have a favorite hand or use both equally.

Now, how many people are left-handed?

Studies using this scoring method found that about 10% of people around the world are left-handed. This means in a group of 10 people, usually, just one is left-handed, and the others are right-handed or mixed-handed.

But, this number might not be totally accurate. In some places, left-handed people have been pressured to use their right hand because of social or cultural reasons.

So, the actual number of left-handed people could be higher than what we think.

Genetics of Handedness

Is Being Left-Handed in Our Genes?

When we think about whether we’re left or right-handed, a big question pops up: is it something we inherit, like eye color or height? Or is it more random with the effect of the environment?

The truth is, it’s a bit of both. There’s good evidence that our genes play a role, especially in left-handedness.

For instance, if you have left-handed family members, you’re more likely to be left-handed too. Twins studies also show that there is a heritability component but it’s not 100%.

This shows us that handedness isn’t just by chance – our genes are involved. But, it’s not as simple as having a left-handed gene that gets passed down.

It’s more complex, with different factors like the handedness of your parents and whether you’re a boy or girl playing a part. Scientists think about 25% of what decides our handedness comes from our genes.

Right-Handedness: Is the Dominant Hand Genetic Too?

Right-handedness is more common and seems to be the standard setup for most of us.

It’s also influenced by our genes but in a different way than left-handedness. Instead of being linked to a specific gene, right-handedness seems to happen when the genes tied to left-handedness aren’t as active.

So, it’s more about the absence of certain genetic factors rather than the presence of a ‘right-handed gene.’

The PCSK6 Gene and Left-Handedness

One key gene that scientists think is linked to being left-handed is called PCSK6.

This gene is part of the recipe for a protein that helps decide which side of the body things like our heart and brain develop on when we’re just a tiny embryo.

It’s part of what makes us not exactly the same on our left and right sides.

This gene, PCSK6, sits on chromosome 15 and has different alleles. One of these versions seems to show up more often in left-handed people.

It changes how the PCSK6 gene works, which then affects the protein it makes. This protein plays a big role in setting up the body and brain’s left-right balance, especially in a part of the brain called the corpus callosum.

This part is like a bridge of nerve fibers that lets the left and right sides of the brain talk to each other.

It’s important for things like language, remembering stuff, and figuring out where things are in space.

It turns out, left-handed folks often have a bigger corpus callosum. This might mean they have better connections between the two halves of their brain, which could be why they’re sometimes really good at creative stuff, solving tricky problems, and doing lots of things at once.

But the whole story about the PCSK6 gene and how it links to being left or right-handed isn’t totally clear yet.

There are other factors, like age, gender, and the world around us, that also play a part. Plus, PCSK6 isn’t the only gene involved – there are likely others that work with it making handedness most likely a multigenic trait.

A few other genes linked to handedness

LRRTM1 (Leucine-Rich Repeat Transmembrane Neuronal 1): This is another most talked-about when it comes to handedness. Research has suggested that variations in LRRTM1 might be linked to left-handedness. It’s interesting because this gene is also associated with the development of certain parts of the brain, hinting at a deeper connection between our brain structure and the hand we prefer.
DIO3 (Deiodinase, Iodothyronine, Type III): DIO3 is part of a complex interplay of genes that might influence handedness. This gene is particularly interesting because it is involved in the regulation of thyroid hormones, which are crucial for brain development. The way it influences handedness could be indirect, by affecting the brain regions responsible for motor skills.
MAOA (Monoamine Oxidase A): This gene is involved in breaking down important neurotransmitters in the brain, like serotonin and dopamine. Some studies have suggested a link between variations in this gene and the probability of being left-handed, especially when considering how these neurotransmitters affect brain functions and development.

How Epigenetics Influence Handedness: More Than Just Genes

Handedness isn’t just about the genes you’re born with. There’s another layer to the story called epigenetic factors. These are like tiny chemical tags that attach to our DNA or the proteins around it, changing the way our genes work without altering the DNA’s code itself.

These epigenetic factors are shaped by lots of things like what we eat, stress, hormones, and even as we age. They can be passed down from our parents or picked up throughout our lives. These factors can have a lasting impact on how our bodies and brains develop and work.

One key epigenetic factor is DNA methylation, where a small chemical group sticks to the DNA and usually turns down the volume on that gene. This affects whether a gene is active or not.

Research shows that this DNA methylation plays a role in handedness. For instance, the PCSK6 gene linked with left-handedness can have different methylation levels in lefties compared to righties.

Even things like the handedness of our parents or our gender can influence these methylation levels. Some studies also found that the methylation of genes involved in brain development is connected to whether we’re left or right-handed and could link to conditions like schizophrenia, bipolar disorder, and autism.

So, epigenetics adds another twist to the story of handedness. It shows us how our genes interact with our environment and can change over time, making the whole left-handed or right-handed thing even more complex.

How Our Environment and Life Experiences Shape Whether We’re Left or Right-Handed

It’s not just our genes that decide if we’re left or right-handed. Our environment and what happens to us as we grow up play a big part too.

Handedness is shaped by a mix of many things, from what happens to us before we’re born to the experiences we have growing up. Let’s dive into some of these factors:

Before We’re Born: Prenatal Influences

Even before we’re born, a lot is happening that can affect whether we’ll favor our left or right hand.

Things like stress during pregnancy, the age of the mother, and even her habits like smoking or drinking can impact the brain’s development. The way a baby lies in the womb and how active they are can also make a difference.

All these prenatal factors can change the way our brain cells grow and connect, which might lead to being left or right-handed.

Birth Experiences: Complications and Effects

What happens during and right after birth can also influence handedness. If a baby is born prematurely, has a low birth weight, or if there are complications like issues with the umbilical cord, it can affect their brain.

Sometimes, these complications can increase the chances of being left-handed or mixed-handed.

Hormones: Tiny Messengers with Big Impact

Hormones in our body, like testosterone and estrogen, can play a role in brain development and, consequently, in which hand we prefer.

These hormones can change how our genes work in our brain cells, potentially affecting whether we’re more likely to use our left or right hand.

Nutrition: Building Blocks for Brain Development

What we eat, especially during early development, can have a big impact on our brain. Nutrients like vitamin B12, iron, and omega-3 fatty acids are crucial for brain health.

Depending on our nutrition, it might influence our likelihood of being left or right-handed.

Infections: How They Can Affect the Brain

If a mother gets certain infections during pregnancy, or if a child gets them early in life, it can affect brain development.

This might lead to differences in how the brain is structured and functions, which could play a role in hand preference.

Injuries: Their Role in Hand Use

Injuries to the brain or body, especially in early life or even later, can influence which hand we prefer. Head traumas, strokes, or even surgeries might lead to changes in how we use our hands.

Education and Culture: Learned Behaviors and Societal Influence

The way we’re taught and the culture we grow up in can influence our hand preference.

If a culture favors right-handedness, a left-handed child might be encouraged to use their right hand more.

Educational activities like writing, music, and sports can also steer us towards using one hand over the other.

Social Influences on Hand Preference

Our family, friends, teachers, and even what we see in the media can impact which hand we use more.

If we’re surrounded by right-handed people, we might be more inclined to use our right hand, even if our natural preference is for the left.

All these factors combine in complex ways to shape whether we’re left or right-handed. It’s a mix of nature (our genes) and nurture (our environment and experiences).

This means handedness isn’t just set in stone by our genes; it’s also influenced by the world we grow up in and live in.

Connection Between Being Left or Right-Handed and Brain Functions

Handedness – whether you’re a lefty or a righty – isn’t just about your hands. It’s really about your brain!

Our brains are split into two halves, and they’re not the same. They have different jobs. This is called brain asymmetry.

This idea of one side of the brain being more dominant is known as lateralization. Both your genes and the world around you play a part in this, and it’s linked to whether you’re left or right-handed.

Language: A Brain’s Task Mostly for the Left Side

Language is a big job for our brains and is mostly handled by the left side. This includes speaking, understanding what others say, reading, and writing.

There are special areas called Broca’s area and Wernicke’s area in the left hemisphere that manage these tasks. But, the right side of the brain helps out too, especially with things like tone of voice and understanding jokes or metaphors.

Most right-handed people (about 90% of us) have their language skills mainly in the left side of their brain.

For left-handed folks, who make up about 10% of people, it’s a bit different. About 70% of them also use the left side for language, but the rest either use the right side or both sides equally.

This difference suggests there’s a genetic link between which hand you prefer and how your brain handles language.

Genes like PCSK6, which are involved in handedness, also play a role in how our brains develop these language skills. But it’s not all about genes – things like what happens to us when we’re growing up, like education, also shape our language abilities.

Spatial Reasoning: More of a Right Brain Thing, Especially for Lefties

Spatial reasoning – the ability to think about objects in three dimensions – is another brain job. It’s mostly up to the right hemisphere.

Left-handed people often have a stronger right hemisphere for this, meaning they might be better at tasks like visualizing different spaces or shapes.

But again, both sides of the brain work together, and right-handed people can also be good at these tasks.

Emotion Processing: Another Right Hemisphere Role

Our emotions are also processed mainly in the right side of the brain. This includes recognizing and managing our feelings.

Left-handed people might have a more active right hemisphere for this, showing stronger emotional responses. Right-handed people tend to use both sides of their brains more equally for emotion processing.

So, whether you’re left or right-handed isn’t just about what hand you write with. It’s a clue to how your brain is wired and how it works, involving a blend of your genes and your experiences.

Left or Right-Handedness Link to Brain Development Disorders

Important disclaimer: This information is intended for educational purposes only and should not be interpreted as medical advice. If you have concerns about your child’s development or suspect a learning disability or neurodevelopmental disorder, please consult a qualified healthcare professional.

Handedness and Dyslexia

Handedness, whether you’re a lefty or a righty, might be connected to certain brain development disorders, like dyslexia.

Dyslexia is a common learning challenge that makes reading and writing difficult. It’s found in about 5-10% of people and is more common in boys than girls.

Studies show that left-handed and mixed-handed people are often more likely to have dyslexia.

This might be because being left-handed is linked to how our brain manages language. It seems like left-handedness and mixed-handedness can affect the typical left-side dominance for language in the brain. This could make language-related tasks harder.

But, being left-handed doesn’t mean you’ll have dyslexia. It’s just that these two things can be influenced by some of the same factors in our brains.

Handedness and Autism

Autism, a condition affecting social interaction and communication, is another area where handedness might play a role. Autism involves differences in brain regions that help us understand and interact with others.

Like with dyslexia, left-handed and mixed-handed individuals might have a higher chance of being on the autism spectrum.

This could be because the way their brains are wired is different, possibly affecting areas that deal with social skills.

Again, some genes are shared between handedness and autism. These genes might influence how different parts of the brain connect and communicate.

Linking Handedness with ADHD

ADHD, a disorder impacting focus and behavior, might also be linked to whether someone is left or right-handed. ADHD is common, affecting about 5-10% of people, and is related to how certain brain areas that control attention and self-regulation develop.

Studies suggest that left-handed and mixed-handed people might have a higher chance of having ADHD.

Handedness and Schizophrenia

Lastly, schizophrenia, a disorder affecting a person’s perception and thinking, might also have some links to handedness.

Left-handed and mixed-handed individuals may be more prone to schizophrenia. This could be related to differences in brain structure and function.

Overall, while handedness – whether you use your left or right hand more – might be connected to these disorders, it’s important to remember that it’s not a direct cause.

Both handedness and these neurodevelopmental disorders are influenced by a mix of genetic and environmental factors.

How Handedness Evolved in Humans and Animals

Handedness isn’t just a human thing – animals show it too. It’s seen in animals like monkeys, birds, and even fish.

In animals, handedness means preferring one limb or side for tasks like eating or building.

The Story of Handedness in Animals

Looking at handedness in animals can give us clues about why and how it evolved in humans. It shows the pros and cons of favoring one side, and how this trait has changed to suit different living situations.

It also highlights how humans and animals are alike and different in this trait.

For example, in some primates like chimps and orangutans, the split between left-handed and right-handed individuals is similar to humans – about 10% left-handed.

But in other primates, it’s an even 50-50 split, and some groups show no clear preference at all.

This variation suggests that handedness has adapted to different environments and social needs.

Tool Use and Handedness

One big factor in the evolution of handedness is tool use. Using tools needs coordination and skill, often favoring one hand.

This has likely influenced brain development and hand preference. In humans, this is especially clear.

Our complex tool use might have driven the evolution of our strong hand preference.

Communication and Social Interaction

Handedness could also be linked to how we communicate and interact with others. Gestures and body language are important in communication, and this might have shaped hand preference.

For humans, with our advanced language and social structures, this could be a key factor in why most people are right-handed.

The Social Side of Handedness

Being part of a group and forming social bonds is another angle to consider. In humans, cooperating and working together might have influenced which hand we favor.

This could explain why right-handedness is more common – it helps in coordination and cooperation within groups.

All these factors – tool use, communication, and social interaction – might have played a role in how handedness developed in humans.

They show how handedness is not just about the physical act of using one hand over another, but is tied to many aspects of life, from brain development to how we interact with our world and each other.

Final Words On Handedness

In summary, handedness is a mix of genetics and the environment and is tied to how our brains are structured.

Whether you’re left-handed, right-handed, or somewhere in between, this trait affects various brain functions and can even be linked to certain learning and developmental conditions like dyslexia or autism.

Handedness is not just about which hand you write with; it’s a window into the brain’s workings, our development, and even our evolution.

Understanding handedness can help us appreciate the unique experiences and challenges faced by left-handed and mixed-handed individuals, especially in a world largely designed for right-handers.

References:

Dr. Sumeet K., PhD

Dr. Sumeet is a seasoned geneticist turned wellness educator and successful financial blogger. GenesWellness.com, leverages his rich academic background and passion for sharing knowledge online to demystify the role of genetics in wellness. His work is globally published and he is quoted on top health platforms like Medical News Today, Healthline, MDLinx, Verywell Mind, NCOA, and more. Using his unique mix of genetics expertise and digital fluency, Dr. Sumeet inspires readers toward healthier, more informed lifestyles.