The gene is a whisper, not a shout.
Cerca de um em cada dez seres humanos navega o mundo com a mão esquerda como guia — uma minoria que a ciência sempre observou com curiosidade. Um estudo publicado na revista Nature Communications, baseado em dados genéticos de mais de 350 mil adultos britânicos, identificou variantes raras no gene TUBB4B que surgem 2,7 vezes mais frequentemente em canhotos, lançando luz sobre os mecanismos celulares que moldam a assimetria cerebral. A descoberta não resolve o mistério da lateralidade, mas revela que as raízes dessa diferença humana são mais profundas do que o hábito ou a escolha — ainda que entrelaçadas com o acaso.
- O gene TUBB4B, responsável por proteínas que sustentam o esqueleto interno das células, aparece mutado 2,7 vezes mais em canhotos, sugerindo que a estrutura celular influencia qual hemisfério cerebral assume o comando do corpo.
- Apesar da descoberta, os fatores genéticos explicam apenas 0,1% da lateralidade — a grande maioria dos casos resulta de variações aleatórias no desenvolvimento fetal, tornando o gene uma pista, não uma resposta definitiva.
- A ligação entre canhotismo e condições psiquiátricas como esquizofrenia e autismo — que ocorrem duas a três vezes mais nessa população — cria uma urgência científica: entender se a assimetria cerebral é um fio comum entre essas realidades.
- Diferenças geográficas na prevalência do canhotismo apontam para a pressão cultural como força capaz de sobrepor tendências biológicas, revelando que genes e sociedade disputam o mesmo território.
Cerca de um em cada dez habitantes do planeta escreve com a mão esquerda. Lady Gaga, Barack Obama, Paul McCartney — todos pertencem a essa minoria que há muito intriga a neurociência. Um estudo publicado esta semana na Nature Communications oferece uma pista genética, extraída do DNA de mais de 350 mil adultos britânicos.
Os investigadores identificaram variantes raras num gene chamado TUBB4B, que controla proteínas responsáveis por construir os filamentos que sustentam o esqueleto das células. Essas variantes aparecem 2,7 vezes mais frequentemente em canhotos. A hipótese é que mutações nesse gene influenciam o modo como o cérebro desenvolve a sua assimetria — o desequilíbrio estrutural que determina qual mão se tornará dominante. No cérebro da maioria das pessoas, o hemisfério esquerdo controla a mão direita; nos canhotos, essa lógica inverte-se.
O cientista Clyde Francks, do Instituto Max Planck de Psicolinguística nos Países Baixos, é cauteloso quanto ao alcance da descoberta: os fatores genéticos explicam apenas 0,1% da lateralidade. A maior parte do traço parece emergir do acaso — flutuações aleatórias nas concentrações moleculares durante o desenvolvimento fetal. O gene é um sussurro, não um decreto.
A descoberta abre também portas para a psiquiatria. Canhotos e ambidestros desenvolvem esquizofrenia ao dobro da taxa dos destros; no autismo, a disparidade é ainda maior. Se o TUBB4B ou as assimetrias cerebrais que influencia têm papel nessas condições, ainda é desconhecido — mas a ligação existe e aguarda investigação.
Francks nota ainda que o canhotismo é menos prevalente em África, Ásia e Médio Oriente do que na Europa e América do Norte, diferença que provavelmente reflete supressão cultural — crianças forçadas a escrever com a mão direita, contrariando a sua inclinação natural. O gene pode estabelecer uma tendência, mas a cultura pode reescrevê-la.
About one in ten people on Earth reaches for a pen with their left hand. Lady Gaga, Barack Obama, Paul McCartney, Justin Bieber—they belong to this minority, a group that has long puzzled neuroscientists. Why does handedness exist at all? Why does it vary? A study published this week in Nature Communications offers a genetic clue, drawn from the DNA of more than 350,000 British adults.
Researchers identified rare genetic variants involved in how cells form their internal structures, and found these variants appear 2.7 times more frequently in left-handed people than in right-handers. The culprit gene is called TUBB4B. It controls a protein that builds the filaments responsible for maintaining a cell's skeleton. When mutations occur in this gene, they seem to influence how the brain develops its asymmetry—the structural imbalance that determines which hand will become dominant.
The mechanics are worth understanding. In most people, the left hemisphere of the brain controls the right hand. Nerve fibers cross over in the lower brain, routing signals from left to right. In left-handed people, this arrangement reverses: the right hemisphere takes charge of the dominant left hand. Clyde Francks, a scientist at the Max Planck Institute for Psycholinguistics in the Netherlands and one of the study's authors, explains that the TUBB4B gene appears to play a role in establishing this fundamental asymmetry during brain development. The rare mutations are more common in left-handers, suggesting that the cellular filaments TUBB4B controls are somehow involved in how the brain decides which side will be dominant.
Yet here is where the story becomes more complicated. Francks is careful to note that genetic influence accounts for only about 0.1 percent of what makes someone left-handed. The vast majority of the trait—nearly all of it—appears to arise from chance. Random fluctuations in molecular concentrations during fetal brain development, unpredictable variations in how neurons wire themselves together, seem to determine handedness for most people. The gene is a whisper, not a shout.
The research team drew their data from the UK Biobank, a repository of genetic information from hundreds of thousands of British volunteers. About 11 percent of the study sample were left-handed, close to the global average. This large dataset allowed researchers to spot patterns that smaller studies would miss—patterns that might otherwise remain invisible.
Beyond handedness itself, the discovery opens doors into psychiatry. Left-handed and ambidextrous people—those equally skilled with both hands—experience schizophrenia at roughly twice the rate of right-handers. In autism, the disparity is even starker: three times more common. Whether the TUBB4B gene or the brain asymmetries it influences play a role in these conditions remains unknown. But the connection is there, waiting to be explored.
Francks also points out that left-handedness is not distributed evenly across the world. In Africa, Asia, and the Middle East, left-handers make up a smaller share of the population than in Europe and North America. This gap likely reflects cultural suppression rather than genetic difference—in many societies, children have been forced to write with their right hand, overriding their natural inclination. The gene may set a tendency, but culture and pressure can reshape it. What this study reveals is that handedness has roots deeper than habit or choice, even if those roots are thin and tangled with randomness.
Notable Quotes
In most people, the left hemisphere controls the right hand. In left-handed people, the right hemisphere takes charge of the dominant left hand.— Clyde Francks, Max Planck Institute for Psycholinguistics
Most people become left-handed simply because of random variations during fetal brain development—changes in molecular concentrations, for example.— Clyde Francks
The Hearth Conversation Another angle on the story
Why does it matter that we found this gene if it only accounts for a tenth of a percent of left-handedness?
Because it's the first concrete biological mechanism we've identified. For decades, we knew handedness ran in families, but we didn't know how. Now we have a protein, a gene, a cellular structure involved. That's the beginning of understanding.
So most left-handed people just... got lucky during fetal development?
Not lucky exactly. Random. Molecules concentrating in slightly different amounts, neurons wiring themselves in slightly different patterns. The brain is building itself in the womb, and tiny variations compound. The gene is there, but it's one voice in a chorus.
Why would schizophrenia be more common in left-handed people if the gene only has such a small effect?
That's the real question now. The asymmetry itself might matter more than the gene. Left-handed brains are wired differently. Whether that difference makes them more vulnerable to certain psychiatric conditions—that's what researchers will be chasing next.
And the cultural suppression angle—does that mean some left-handed people are actually right-handed underneath?
Possibly. If you forced a child to write right-handed for years, you might override their natural dominance. But the brain asymmetry would still be there. You'd have a person whose hand was trained one way and whose brain was wired another.
What comes next for this research?
Looking at whether TUBB4B or brain asymmetry itself plays a role in schizophrenia and autism. Understanding why left-handedness correlates with those conditions. And probably finding more genes involved—this one is just the first piece.