Genes play a very small role in determining left-handedness, research finds

AYESHA RASCOE, HOST:

If you're left-handed, like me, you know you are one of a rare and special breed. Just 10% of the world's population is estimated to be left-handed, but many common conceptions about left-handedness turn out to be wrong, starting with that it's definitely hereditary.

CLYDE FRANCKS: We actually think that most of the left-handedness in the population is not caused by genetic variants.

RASCOE: Clyde Francks is a geneticist and neuroscientist at the Max Planck Institute for Psycholinguistics in the Netherlands. He led a team that just published a paper about left-handedness in the journal Nature Communications.

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FRANCKS: It's probably just kind of random fluctuations of chemicals in the very early developing brain in the embryo.

RASCOE: That surprised me. My mother's right-handed, but all of her children are left-handed. We thought being left-handed must have something to do with the genes we inherited. And it's even stranger because we don't all have the same father.

FRANCKS: The heritability of left-handedness is actually quite low. So in studies of twins, it's been measured at about only 25%. So in most people who are left-handed, there will not be a simple genetic explanation just running through the generations in a clear way.

RASCOE: But in the new research, Francks and his team did discover one gene that sometimes has an effect on which hand is dominant.

FRANCKS: What we knew before this study was that there were various common variants in the genome that had very, very tiny effects on the probability of being left-handed. And so what we did in the latest study was a quite different approach. We were looking for variants in the genome that are very rare in the population and are located in the specific parts of the genome that code directly for the proteins that our bodies are made of. And those kinds of genetic variants can actually have quite large effects on human traits when they're present in a small number of people.

RASCOE: The gene they analyzed is called TUBB4B. If someone has a particular variant of this gene, Francks says that person is very likely to be left-handed. But very few people, even very few left-handed people, have this variant.

FRANCKS: They're very rare in the population, so they would only be accounting for about 1 in 1,000 left-handers at most.

RASCOE: It's still very much a mystery why the vast majority of left-handed people are that way. His idea about random fluctuations of chemicals in the embryo is also unproven. But what about this question?

I've also heard that left-handed people are more creative because the left side of the body's controlled by the right side of the brain, and that's the creative side. Is that true?

FRANCKS: Yeah. I mean, I don't think that's true. No.

RASCOE: (Laughter).

FRANCKS: I know that this is - it's a popular thing. That's too simple. The differences between the hemispheres of the brain are much more subtle and complex than that, and each side is doing important things in any particular task that you're doing.

RASCOE: OK, so - but we are very special if we're left-handed. Science has confirmed that, right?

(LAUGHTER)

FRANCKS: Well, 10%, you know? You decide how special that is.

RASCOE: Oh, well, thank you. I appreciate that. I'll take that. Thank you so much. Clyde Francks, a geneticist at the Max Planck Institute for Psycholinguistics in the Netherlands. Thank you so much for joining us.

FRANCKS: Thank you.

(SOUNDBITE OF LITTLE COMETS SONG, "JENNIFER") Transcript provided by NPR, Copyright NPR.