Why are more people Right-handed than Left-handed?

[ZedNova]

Why are more people right handed than left handed? And how come in certain countries more people are left-handed than right-handed?

Do animals have a preference as to which hand they use? How did this happen in nature?

[TooManyErrors]

Its probably the way humans evolved, and animals do have a preference to what hand/paw/claw they use.

[Deadpangod3]

I can't figure out how people can POSSIBLY be right handed...

If I lose my left hand I'm screwed

[TooManyErrors]

I can't figure out how people can POSSIBLY be right handed...

Genetics, natural selection, and evolution, thats how.

Edited June 5, 2013 by TooManyErrors

[Ancasta]

It depends on many factors. I thought I was ambidextrous as I used both hands for all tasks, however, since I have been working I have switched to use my left hand and find my right-hand writing to get worse and worse. Why switch to my left? Well, my desk is arranged so that my note pads are all on my left while my mouse is in my right hand.

It is nothing more than dominance of one side over the other at a young age that really determines an individual's preferred hand. There are other factors that contribute, the biggest being society. None-asymmetrical things, over time, have a tendency to be built for right handed people and this societal preference may impact the choice of preferred hand.

I believe there is a field of neurology that you'd have to be an expert in before you could answer it correctly but the basics are pretty easy.

[softweir]

It isn't just society and tool design - people in traditional societies where there is a dearth of asymmetrical tools also show a very strong preponderance of right-handedness for most tasks.

Some animals show handedness, but the rules are somewhat different. Macaques (iirc) are very "handed" and each will only ever use one, "preferred" hand for putting food in their mouths and will carry food in the other hand. However macaque society is split 60/40 between left/right handed.

There has been a suggestion that the dominance of right-handedness in humans is a trait that makes it easier to learn complex tasks from other people, but the reasoning given was rather vague. It feels convincing, and I can report that a left-handed friend tried to teach me some knots and the difference in handedness made learning unusually difficult. I am also told that young left-handed signers tend to reflect gestures and that this can cause confusion.

But all that is speculative: nobody really knows the reason!

[Rickenbacker]

Random chance, is my best guess. One hand had to be dominant, since most people can't use both equally well, and it just turned out to be the right in most cases.

[softweir]

Equally, one could say "it's random chance the heart and stomach are on the left". Yet in that case there is a lot of detailed genetics and biology that ensure consistent chirality. Yes, it is random chance that all that hard-wired genetics came to "choose" the left, but it is not random chance that a preferred position came about.

In the case of handedness, the very high bias towards right-handedness strongly suggests that there is some powerful advantage to humans having consistent handedness. We don't know what that advantage is and nor do we know the mechanisms involved, but to say there is no advantage and no mechanisms is possibly going to far.

[rryy]

I'm not an expert, but my thinking is that because humans' defining trait is logic and critical thinking, which are controlled by the left side of the brain, people are mostly right handed because the left side of the brain controls the right side of the body.

[Temstar]

It's language. Most early writing tools and ink based. For a left to right written language the right hand has a huge advantage because by the time you go to a new line and run your hand over the previous written line the writing would have (hopefully) already dried, thus causing no smudging. A left handed person writing a left to write language will run his hand immediately over the text after writing it and cause serious smudging issues.

Direction of the language is a lot more random though, ancient Chinese for example was written top down then right to left in vertical columns because it use to be written on stripes of bamboo stringed up into a roll.

[Kryten]

Rryy; That can't be it, because the 'left brain logical, right brain artistic' thing is mostly nonsense.

Temstar; That also can't be it, the ratio is roughly the same (70-90%) throughout the entire planet, regardless of whether the people traditionally wrote left to right, right to left, or indeed at all.

Edited June 6, 2013 by Kryten

[Kerbface]

My hypothesis would just be that it just went one way by random chance and then had a sort of a snowball effect with the slightly more common (by chance) right handers began teaching their children to use the same hand as them until it eventually became biologically ingrained, like an instinct.

[M83]

It's language. Most early writing tools and ink based. For a left to right written language the right hand has a huge advantage because by the time you go to a new line and run your hand over the previous written line the writing would have (hopefully) already dried, thus causing no smudging. A left handed person writing a left to write language will run his hand immediately over the text after writing it and cause serious smudging issues.

This seems like a somewhat verifiable reason since as a left-handed person, handwriting essays and doing things like Scantron testing become an awful pain of smudged marks and a side of the hand covered in graphite/ink.

Of course, my example doesn't have much to do with evolution since Scantrons didn't exist thousands of years ago.

Another good thing to raise is the whole "left-handed people are statistically better at certain things than right-handers" and vice versa. Just my $0.02.

[Dunbaratu]

Before trying to find the biological reason for right-handedness, I think it's first necessary to test to find out if it's nature or nurture, and that's going to be VERY hard to do in an ethical way. (It requires experimenting on babies before they learn anything from watching people.) It might not be hardwired biologically. It might be culturally learned, which would account for why it's not 100% consistent. Our bodies are not entirely symmetrical, but we're all non-symmetrical in the SAME consistent way. You don't have some people with the heart slightly to the left and other people with the heart slightly to the right, for example, nor do you have 10% of the population with their digestive system mirrored such that the stomach slants the other way, and so on. These things are not like handedness, where there is one dominant likely trend but yet a very large minority that end up the other way.

It's definitely a matter of the brain and the brain's muscle control algorithms (most of which are in the cerebellum and not the cortex), but the brain is a mixture of SOME things that are pre-programmed in foetal development and SOME things that are wired after birth. For example, the brain comes pre-programmed to be ready to map sounds symbolically to ideas, so language can happen, but it does not come pre-programmed to know exactly which muscles to move in which way to make which sounds - that has to be learned which is why speaking the phonemes in foreign languages that are not in your native language is hard - you didn't group up teaching your mouth to make those sounds as a baby.

It's believable that there's an advantage to having most of the population having the same dominant side. It's just unclear whether this is passed on genetically or memetically.

[drakesdoom]

How about that early bronze age battles revolved heavily around close formation tactics that favored right handed men thus weeding out left handers?

[softweir]

It's language. Most early writing tools and ink based. For a left to right written language the right hand has a huge advantage because by the time you go to a new line and run your hand over the previous written line the writing would have (hopefully) already dried, thus causing no smudging. A left handed person writing a left to write language will run his hand immediately over the text after writing it and cause serious smudging issues.

Direction of the language is a lot more random though, ancient Chinese for example was written top down then right to left in vertical columns because it use to be written on stripes of bamboo stringed up into a roll.

That's a tempting hypothesis.... But I fear handedness probably predates writing by a very long interval. In any case, ink and paper were very late inventions, and media such as stone-scratching and clay-marking are very much less susceptible to smudging than ink-on-paper!

In any case, for writing to drive handedness, having the "right" or "wrong" hand would have to exert a very powerful influence on survival to have had such an effect in such a very short space of time (in evolutionary timescales), and smudging your work is most unlikely to cause sterility or death!

[softweir]

How about that early bronze age battles revolved heavily around close formation tactics that favored right handed men thus weeding out left handers?

Or, indeed, would pre-stone-age hunting groups have benefitted from handed preference?

[lyndonguitar]

Rryy; That can't be it, because the 'left brain logical, right brain artistic' thing is mostly nonsense.

There is a widely popular and accept theory about what he said, Although It doesn't say any logical or artistic brain sides, it definitely talks about the two brain hemispheres that maybe the possible reason of handedness.

[Comrade Jenkens]

ambidextrous ftw

[Kerbface]

How about that early bronze age battles revolved heavily around close formation tactics that favored right handed men thus weeding out left handers?

I'm not sure what you're referring to but is there a reason the technique could not have been mirrored? It could have been a way to weed out one of the two hands, but I still wonder if it was just chance or is there some other basis? And the other thing is, do we know if all societies had the same dominant hand that was used in battle formations? If far disconnected cultures evolved right-handed tactics simultaneously, that would suggest some inherent right-handed trend in humans.

[Jokurr]

For that matter, is left handed vs right handed a trait that is genetic? For them to be weeded out through bronze age battles, it would imply that the offspring of left handed people would be more likely to be lefthanded themselves. Is there any correlation there? Both of my parents are left handed but I am right handed. That's just me though, I don't know if there is a trend.

[drakesdoom]

I'm not sure what you're referring to but is there a reason the technique could not have been mirrored? It could have been a way to weed out one of the two hands, but I still wonder if it was just chance or is there some other basis? And the other thing is, do we know if all societies had the same dominant hand that was used in battle formations? If far disconnected cultures evolved right-handed tactics simultaneously, that would suggest some inherent right-handed trend in humans.

I do not know of any society that developed left handed formations, though that is not proof by a long stretch. I would imagine a shield on the left arm would be more effective though at increasing survival as from an organ standpoint the right side of the torso is slightly more expendable. The torso expend-ability may explain it at an earlier stage in where only very simple tools where available for hunting, at the bronze age it would only reinforce existing trends.

For that matter, is left handed vs right handed a trait that is genetic? For them to be weeded out through bronze age battles, it would imply that the offspring of left handed people would be more likely to be lefthanded themselves. Is there any correlation there? Both of my parents are left handed but I am right handed. That's just me though, I don't know if there is a trend.

Handedness does not need to be genetic for this to have an effect. If more left handed men died and their children died or were taught a trade by surviving right handers that could easily cause a reinforcing pattern. I would go so far to say even if one was genetically left handed or had a body dis-symmetry making left handed actions easier you could still go through life right handed if you were always taught to use your right hand. The roman catholic church in the dark ages held very strict rules about using the left hand for example.

[Dunbaratu]

Or, indeed, would pre-stone-age hunting groups have benefitted from handed preference?

Also, when talking about genetics, it's always very important to remember just how YOUNG the Homo Sapiens species is compared to a lot of other forms of life. Bronze age wasn't that long ago, genetically speaking.

Such explanations for right-handedness would work if it's passed on as a meme, but not so much if its passed on as a gene.

[itstimaifool]

Before trying to find the biological reason for right-handedness, I think it's first necessary to test to find out if it's nature or nurture, and that's going to be VERY hard to do in an ethical way. (It requires experimenting on babies before they learn anything from watching people.) It might not be hardwired biologically. It might be culturally learned, which would account for why it's not 100% consistent.

We could just watch children who are raised in families with both parents being left-handed, and see if they are more likely to be left-handed. I would call this ethical. Just give them some toys to play with that could demonstrate handedness, and watch them play for an hour or so every few months. More of an observation than an experiment, but I think it could accomplish the same thing.

[Sᴄɪɴᴛɪʟʟᴀᴛᴏʀ]

There are more right-handed people alive and so there are more right-handed children born, genetics. Its a cycle that goes back a few million years where a tribe of lefties got eaten by lions and lost their spot in the gene pool.