Why Are Some People Left-Handed?

More than 2,500 left-handed people are killed each year whilst using equipment designed for right-handed people, the most dangerous of which is the right-handed power saw Life sure can be hard for a lefty

The word right is synonymous with the word “correct” whereas “left” comes from Old English where it meant “sinister” and “evil” In old England Left-handedness was actually believed to have come from the devil So if left-handedness is such a disadvantage then why are between 10% and 12% of the population still left handed? After all, evolution typically weeds out imperfections within a species But scientists have found evidence that as far back as 500,000 years ago, 10% of humans were left-handed; it’s always been this way So there must still be some advantage to being left-handed, even in the modern world

So what is it? Left’s find out Contrary to some theories left-handedness is not learnt as a child It’s not simply a matter of which hand a child chooses to write with from an early age If this were true, the numbers would be closer to 50/50 for left and right-handedness But only 10% of the population is left-handed

In fact we can actually tell if a baby is going to be left or right-handed when they’re only a couple of months old When you place a baby on its tummy, babies’ who will grow up to be left-handed will typically turn their heads to the left, whereas right-handers do the opposite Before you go haphazardly flipping over babies to try this out for yourself, you should know it’s not an entirely accurate way to tell, but research has shown there’s a strong correlation So if we don’t learn left-handedness, then where does it come from? Statistics suggest we’re born with it; it’s in our genes Two right-handed parents have a 9% chance to give birth to a left-handed child

When one parent is left-handed that rises to 19% and when both parents are left-handed the chance is 26% These statistics suggest that handedness is at least somewhat hereditary But left handedness is highly unusual, because it’s not simply caused by dominant and recessive genes About 90% of people are right-handed, suggesting that right-handedness is an extremely dominant trait Based on what we know about genetics, a gene that is so fiercely dominant, in this case right-handedness, would have forced the recessive gene, left-handedness, out of the gene pool a long time ago

In theory, we shouldn’t have left-handed people Yet we still do and the percentage of people that are born left-handed isn’t decreasing like it theoretically should do In fact, it has stayed exactly the same for thousands of years This suggests that handedness isn’t caused by a simple case of dominant vs recessive genes It’s considerably more complex than that

It’s likely to be caused by a whole mix of different genes or perhaps something completely different altogether The truth is that, why some people favour one hand over the other is still a bit of a mystery There is one theory however that is the most commonly accepted answer to this perennial question Researchers think handedness is actually caused by something called “brain lateralisation” Our brains are divided into two hemispheres, left and right

For the sake of efficiency our brains like to use different regions for different tasks Two of the most energy intensive activities that humans do are language and using our fine motor skills So our brain clusters the control of these activities into one side of our brain, rather than having it spread out all over the damn place This makes those tasks more energy efficient Most people’s language and fine motor skills are controlled by the left hemisphere of their brain and each hemisphere generally controls the opposite side of the body

So it makes sense that most people would be right handed, because in most people, the majority of the processing which controls the movement of muscles is done in the left hemisphere of the brain, which is the hemisphere that controls the right hand side of the body In fact, in 90% of right-handed individuals, they use the left hemisphere of their brain to control language and fine motor skills Whereas, a considerably lower 61% of left handers control these skills using the left side of their brain In most animals the hemispheres of their brain divide the processing of tasks equally, those same animals have no hand preference Whereas human brains tend to specialise functions to either one side of the brain or the other and consequently we also favour a particular hand

This strong correlation has led biologists to think that brain lateralisation is closely linked to handedness Left-hemisphere brain lateralisation is a common trend amongst left handers but it doesn’t fully explain why people are left handed After all, 61% of left handers still use the left hemisphere of their brain, the same side that right handers use Researchers at Pennsylvania State University believe handedness it caused by genes Their theory is that there are two distinct alleles of a gene which causes handedness

An allele is a variation of a gene One of those alleles is known as the D gene, which stands for “dextral”, meaning right The other allele is called the C gene, which stands for chance The D gene is the most common in the human gene pool and when it is present, the person will be always be, right-handed You may therefore think that the presence of the significantly less common C gene, will mean the person is left-handed

But it’s known as the chance gene, because when it’s present, the hand preference of the person will be random, there will be a 50/50 chance of that person being left or right handed This means that there’s a third class of handedness There’s a small percentage of people who have some degree of ambidexterity Being ambidextrous means one is equally as proficient with both hands Since genes come in pairs, every human has one of three combinations of the aforementioned D and C genes

The first combination is DD, meaning the person has a strong right-handed bias The second combination is CC, meaning there’s a straight up 50/50 chance the person will be either left or right-handed But the third combination is quite unusual; the third possibility is DC, one of each gene variation People with both a D (right-handed) and a C (chance) gene, are usually most proficient with their right hand, but they are also perfectly capable using their left hand People who have a DC gene combination are somewhere in the spectrum of being semi-ambidextrous to fully ambidextrous

Such people make up only 1% of the population So if you are one of the 1% that can adequately use both hands, well done, you have a very rare set of genes But if you are left-handed it’s not all bad news There’s numerous benefits to being a lefty Lefties are sought after in competitive sports

Since most players are right-handed, a lefty can surprise and unnerve their opponent, gaining the advantage Because most players are used to fighting right-handed opponents, not left-handers Sports where left handers have such an advantage include tennis, baseball and boxing, to name but a few Also, scientists aren’t quite sure why, but lefties are considerably more likely to being a genius than righties For example, 20% of Mensa members are left-handed, which is a disproportionately large amount when you consider that only 10% of the population are left-handed

Some believe lefties are more intelligent because throughout their life, they’ve been forced to use and workout both sides of their brains instead of just the one Also an unusually high percentage of US Presidents have been left handed Including Barack Obama, Bill Clinton, George HW Bush and Ronald Reagan

There are endless benefits to being a lefty, so even if the word “left” is synonymous with being evil, don’t worry Next time your friend teases you for being a lefty, just remind them that you’re considerably more likely to be accepted into Mensa and you stand a much better chance than they do at becoming president

About Thoughty2

Thoughty2 (Arran) is a British YouTuber and gatekeeper of useless facts. Thoughty2 creates mind-blowing factual videos, on the weirdest, wackiest and most interesting topics. Combining fascinating lists with answers to life's biggest questions.

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