Scientists spent decades searching for it. What they found was far more interesting.
It seems obvious, doesn't it? Left-handedness runs in families. So there must be a "left-handed gene". Find it, and you've solved the mystery.
For years, scientists thought exactly the same.
Researchers combed the human genome looking for the switch that made someone left-handed. Every few years a new candidate made headlines. A gene called LRRTM1 looked especially promising, excitement grew, and then other researchers failed to confirm the finding. This pattern repeated for the best part of a decade.
The problem wasn't the research. It was the question.
Not one gene. Hundreds.
The breakthrough came when scientists stopped hunting for the left-handed gene and analysed genetic information from more than a million people instead.
Rather than one gene, they found dozens — perhaps hundreds — each making a tiny contribution. No single one of them decides which hand you will favour.
Think of it less as a switch and more as a committee vote, held by your cells, before you were born.
And genes only take you so far. Twin studies suggest they account for roughly a quarter of the variation in handedness, which is also why most children of two left-handed parents still turn out right-handed.
The story may begin before you are born
Some of the most intriguing findings involve genes that help build microtubules — the microscopic scaffolding inside every cell.
A large UK Biobank study published in 2024 found that rare changes in one of these genes, TUBB4B, were nearly three times more common in left-handers.
Worth keeping that in proportion. These variants are rare in everybody: roughly one left-hander in 1,300 carries one, against one right-hander in 3,600. They explain only a sliver of left-handedness. Their value lies in what they point towards.
Because if microtubules are involved, the foundations of hand preference may be laid while your cells are still organising themselves — long before there was a brain to direct anything, and long before you could have reached for something.
The biggest surprise
Even with all these genetic influences identified, scientists still cannot reliably predict whether a particular person will be left- or right-handed.
Genes are only part of the story. Development before birth matters, and so does an element of plain biological chance.
That is why identical twins, who share virtually the same DNA, don't always share a hand preference. Researchers call it developmental randomness — tiny differences along the way that produce different outcomes from nearly identical instructions.
The bottom line
Modern genetics answered the question largely by dismantling it.
There is no single left-handed gene waiting to be found. There are hundreds of small nudges, a great deal of early development, and a measure of luck.
Which means the honest answer to "where did it come from?" isn't your mother's side or your father's. It's all of them, none of them in particular, and a roll of the dice.
Enjoyed this Quick Read?
This article is the second part of The Science of Left-Handedness — a collection of short, easy-to-read guides from Anything Left-Handed on what modern research really tells us.
Curious why those early gene discoveries kept falling apart? Our full research review follows the story from the first candidate genes to studies of more than a million people, and is clear about how much still isn't explained.
For the full picture, read The Genetics of Left-Handedness.
Written by Anything Left-Handed
Specialists in left-handed products and information since 1968. We have been collecting left-handers' own accounts for longer than most of this research has existed.
We are not geneticists. We read the published research carefully, we say where the evidence is thin, and we correct ourselves when we get something wrong.
The research behind this: Cuellar-Partida G et al. (2021), Nature Human Behaviour - genome-wide study of approximately 1.7 million people. Schijven D et al. (2024), Nature Communications - rare variants in TUBB4B. Full sources are listed in the detailed review.
Last reviewed October 2026.
Over to you. How far does left-handedness run in your family — and does your family's pattern fit what you expected?
Comments 9
My mother's parents and siblings were right-handed. My father's parents and siblings were right-handed. Of their eight children, only my older brother and I are lefties. My brother is more of a lefty than I, being a "hook" writer, etc.--as someone mentioned, his right hand is basically useless to him. I am sort of a split. I do most things left-handed, but I use my right, too. I don't hook-write (I was taught to angle the paper to my left hand instead of the right; no smears for me) and I use right-handed scissors better than left. That is, I was able to adapt better than he to our right-handed world. (However, I approach things in a left-handed way that sometimes causes issues when dealing with machines, drinking fountains, etc. which favor right-handers. Thus is the life of a lefty!) Both his children are right-handed, as is his wife.
Of my parents other six grandchildren (eight in all), only one is a lefty--and was born to one of our right-handed brothers (our youngest sibling). His wife was a right-hander. She's a lefty more like her uncle than her aunt, a hook-writer, right-hand-almost-useless type. The remaining five grandchildren are righties born to two right-handed parents.
And, wondering about those "nudges," Her father spent a lot of time as a kid hanging out with his older brother. Though he was right-handed, our younger brother learned how to do a lot of things in a left-handed way because that's how he was taught. For example, he coils ropes, etc. as a lefty. I taught him how to tie his shoes, so he ties his shoes as a lefty. Did those nudges help nudge handedness in his daughter? Or, was he a closet lefty trapped in a righty world that adapted even better than I did??
Interesting.
I also have an ant on my dad’s side of the family that is left-handed, and she has one out of her three children that is left-handed. My Husband’s brother is also left-handed
Even though the research says that they cannot find a specific gene, I do believe left-handedness runs in families.
The finding isn't that handedness isn't inherited — it's that it isn't inherited through one gene. Hundreds of genetic influences each add a nudge, which is why it clusters in families like yours without following any predictable pattern.
Twin studies put the genetic contribution at roughly a quarter.
En 4 generaciones, 4 abuelos, cons sus 12 hermanos; dos padres, con sus 17 hermanos y mis 5 hijos, sin descendencia aún,
41 personas diestras (Me incluyo),y solo yo, zurdo
Interesdante.
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