When do children become right- or left-handed?

Getting our daughter to eat a variety of solid food is work in progress (messy, tantrummy progress) – so for some reason, we thought it might also be a good time to teach her to feed herself with a spoon. She has as much coordination using a spoon as I would have balancing a broom on my nose after a bottle of wine. Though, having said that, it seems that her left hand has slightly better aim than her right hand. And it’s not only at the dinner table that I’ve noticed this – pointing at the neighbour’s cats, tearing books off the bookshelf, poking me in the eye when I’m pretending to be asleep – it seems to be left more than right.

So do we have a Lefty in our house? Or are these observations just my imagination – is it too early for her to have a dominant hand?

By human hands

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As humans, we’re not unique in preferring one hand over another – there are plenty of species in which individual animals have a ‘preferred hand’, or ‘laterality’ as it’s often known – parrots, humpback whales, elephants, snakes, bush babies, rats, cats, and opossums, to name a few. But where man differs from beast is how strongly humans favour the right hand. Across the world, human civilisations of all ethnicities are between 75 and 95% right-handed. Most animal species are 50-50 left- and right-handed (/footed/flippered) – even our closest relatives, chimpanzees, only have a weak preference for using their right hand.

Evidence of a bias towards right-handedness dates as far back as modern humans have existed. For example, stones used for sharpening bone scrapers found in Jersey, dating back as far as 240,000 years ago, are shaped as if they were best used by right-handed neanderthals. Another example: stencils of hands on cave walls in France and Spain, dating back around 11,500 years, are mostly of left hands – suggesting that the right hand was careful tracing around the left hand, or holding a blow-pipe to spray paint onto the wall.

Why do we have handedness at all?

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All parents have done a bit of high stakes juggling in their time – carrying a child in one arm, trying to pick up a toy with the other, whilst balancing a changing bag on the shoulder and holding a phone under the chin. It would be a hell of a lot easier with four arms, but just being ambidextrous would help. So why do we have a preferred hand at all? Why aren’t we just able to use both hands equally?

In an interesting research paper which shows chimps preferentially use their right hand only when standing upright like humans, one theory has been put forward which could explain how the strong preference amongst humans for right handedness evolved, in two stages.

The first thing to emerge was a preference for using different hands for different tasks. This laterality allows the division of labour between two sides of the body – for example, one hand that is frequently used for fine controlled careful movements, and the other hand which is less frequently used, for supportive roles. This doesn’t stop at the hands either, as the work of the brain is also divvied up between the left and right sides. As one example, the part of the brain which deals with language is most often located on the left side.

Then in the second stage, one preferred ‘direction’ of laterality evolved across the human species. One leading theory to explain this is that it enhances cooperation between individuals. Coordinating behaviour is much easier when you think and behave in a similar way – so over time, it would be an advantage for the ‘direction’ of the wiring of the brain to be aligned across the species. Going back to the example of language being in the left side of the brain, in fact this bias is much stronger than the bias towards using the right hand. In this context, right-handedness is little more than a byproduct of an alignment in the way our brains are wired.

How early does handedness start?

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Like us, many parents will claim to have spotted the signs of right- or left-handedness in their child at various points. And it is true that the preference for using one hand over the other occurs early on in childhood – but exactly how early is subject to some debate.

It appears that it might depend on the job at hand (ahem). When children are given a task that involves building blocks, they do not have a ‘dominant’ hand until around the age of 4. However, when babies are faced with a task that involves eating something small, like a Cheerio, babies as young as 1 year old show a preference for using one hand to pick it up (or, if you’re like our daughter, shovel it in as fast as possible).

But recent research has demonstrated that hand preference may appear before a baby is born. A study published in 2017, observing unborn babies using ultrasound, shows that foetuses at 18 weeks can have a preferred hand for careful tasks like touching their face. What’s more, the foetuses’ preferred hand at 18 weeks correlated well with what would become their ‘dominant’ hand as a child, observed at 9 years old. However, for less delicate tasks, like punching the inside wall of their mother’s womb, they weren’t so fussy about which fist they used.

Other research suggests that this propensity to use one hand over the other can occur even earlier. Foetuses at 15 weeks preferentially suck the thumb on their right hand, a preference which is connected to handedness observed at 10-12 years of age. Even earlier than this, 75% of foetuses at 10 weeks move their right arm more than their left.

One fascinating aspect of this research is that moves at this early age are not under the control of the brain – babies aren’t really able to consciously control their own movements until much later on, maybe second trimester onwards – the part of the brain which controls voluntary movements isn’t yet connected to the limbs via the spinal cord. The limbs are instead moving because of nerves firing off in the spinal cord. This suggests that there could be differences in the spinal cord even earlier than than any obvious movements.

Giving weight to this idea, research published in 2017 shows that differences between the left and right side of the foetal spinal cord can be seen from as early as 4 weeks and are well established by 8 weeks post-conception. It’s difficult to say whether or not these differences translate into handedness at a later age, but nevertheless, I think it’s fascinating that even at this early stage, we’re not as symmetrical as we might have thought.

So it’s entirely possible that our daughter may be grow up to be left-handed – ahead of her, a lifetime of lefty-scissors, left-handed guitars, and awkward boxing stances. But in the meantime, we’ll continue to be patient whilst she paints herself with yogurt with a spoon both hands.

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