Left-Handed? That May Have Happened in the Womb

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According to conventional wisdom, babies are born with the ability to be right or left handed. But it turns out that handedness is decided well before birth.

New research from scientists at the Universities of Oxford, St Andrews, Bristol and the Max Plank Institute in Nijmegen, the Netherlands reveals a network of genes that are likely associated with establishing a left- or right-handed bias in embryos. Only about 10% of humans are left-handed, and previous theories focused on everything from which thumb babies start sucking in the womb, to the role of hormones like testosterone .

(MORE: Happy Left-Handers’ Day! What Science Says About Handedness)

But by conducting a genome-wide association study — in which scientists compare a wide array of genetic differences in right- and left-handed people — in four different population groups, the research team found that variants in the gene PCSK6 contributes to handedness determination. This gene is intimately involved in turning a spherical ball of equally oriented cells into an embryo that has discernible left and right sides. Defects in the gene in mice, for example, cause organs to be misplaced, such as having the heart develop on the right side and the liver on the left side. These influences also appear to determine handedness, or relative dexterity, at a level greater than would occur by mere chance.

(MORE: Brain Science: Does Being Left-Handed Make You Angry?)

Although the findings, published in the journal PLOS Genetics, bolster the argument for a genetic component to handedness, the researchers stress that genes may only be part of what determines right- or left-handedness. There is equally solid evidence supporting the role that training and behavior have on whether someone favors the right or left hand, for example, so understanding how genes influence the asymmetrical development of body and brain provides a broader appreciation of how both nature and nurture contribute to dexterity.

7 comments
lefty.mommy
lefty.mommy

I am the only lefty for many generations on both sides of my family and all three of my kids ended up being lefties. I love it but am perplexed as it is a recessive gene and have no idea where it came from. ..

hummingbird
hummingbird

It was interesting to read a study that said the majority of people with autism are left handed. It made me wonder if a recessive gene is responsible for left handedness.

hummingbird
hummingbird

My point is that being left handed isn't dominant in our population so I'm wondering if a recessive gene causes it and not a dominant gene. You do have to wonder also why autistic people tend to be left handed and not right handed.

ettinacat
ettinacat

@hummingbird Dominant vs recessive is not related to the frequency of the gene in the population.

For example, achondroplasia (a certain kind of dwarfism) is a dominant genetic trait, but most people aren't achondraplasic.

If the two alleles are equally common, then the dominant trait will be expressed in 75% of the population. But in most cases one allele is more frequent than the other. For example, if 90% of people have two copies of the recessive allele, then the dominant trait will be seen in only 10% of people.