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

[BigFatStupidHead]

I always thought handedness was genetic, but it seems like it's more complex than that. There is undeniably a genetic component to it, but many other factors seems to contribute more than genetics.

Interestingly, the chirality of the internal organs is determined by the uniform beating of cilia inside the developing embryo. There are interesting diseases that occur when these cilia beat improperly, which often also present with arbitrary asymmetry of the organs. Dr. No (of James Bond) had his heart on the wrong side of his body.

[ZedNova]

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 would make sense, but couldn't written language have developed to be written from right to left? I suppose it's just pure chance that it came out the way it did.

[Aladran]

Look at Lobsters, some have the big claw on the left, other on the right.

[dimovski]

Im left...in both ways of understanding it.Funny BOTH arent as common as RIGHT.

But yeah, I heard we lefties are better at maths...and we die sooner...ugh.

[Godot]

I always thought handedness was genetic, but it seems like it's more complex than that. There is undeniably a genetic component to it, but many other factors seems to contribute more than genetics.

...

It could also be connected genetics ...

say, that right handedness itself isn´t as important, but that it is genetically connected with another component that on teh other hand increases survival by a large margin

(or at least incresed, at soome point in the past).

Fact is, that other animals show side preference as well ...

pigeons for example show a preference with regards to the direction in which they turn (counter-clockwise IIIRC) which is the same as humans, if they are exposed to a similar setting

[Dunbaratu]

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.

For this to be an effective test you'd have to differentiate whether the children are adopted or biological offspring of the families they're raised with. If they're biological offspring then you can't tell if it's nature or nuture. If they're adopted then it's clear you're only looking at nurture not nature.

[Dunbaratu]

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.

I don't believe the language hypothesis because it would have to mean that in the middle-east where the dominant languages are Arabic and Hebrew, people would be predominately left-handed, and that's not what we see.

[BigFatStupidHead]

Im left...in both ways of understanding it.Funny BOTH arent as common as RIGHT.

But yeah, I heard we lefties are better at maths...and we die sooner...ugh.

The lower life expectancy of lefties is due to environmental consequences... we're more apt to turn into oncoming traffic in an emergency (pulling to the left is rather bad in countries that drive on the right)

[ilupper]

My hypothesis is that humans advanced over other hominids because of our throwing skills. 90% of world population lives in the northern hemisphere and this necessitates 90% of us to be right-handers.

http://ilupper.blogspot.com/2011/12/right-handedness-addendum-to-i-need.html

[allmappedout]

For this to be an effective test you'd have to differentiate whether the children are adopted or biological offspring of the families they're raised with. If they're biological offspring then you can't tell if it's nature or nuture. If they're adopted then it's clear you're only looking at nurture not nature.

But you still would need to account for bias. Certainly, as a left hander, I'm keen for my child to be left handed so that I can pass things down, such as my guitar, etc, so I would encourage it. If it isn't 100% one or the other, then you would need to take this into account as the child could become left handed because they're mimicking, or because the parents are making them.

[Bacterius]

I've always imagined that I turned out left-handed because I observed my parents write from across a table at a young age and tried to imitate them without accounting for mirror symmetry (so I thought their left hand was their right hand and vice versa). It's probably not it, but it's as good a guess as any as far as I'm concerned, since it's not particularly important to me. Interestingly I am right-handed for everything else, computer mice, ..

[Aescwulf]

being left handed or right handed, I don't think its nurture, I am right handed and have two brothers, one is left handed and one is right handed. He had no trouble with anything while looking and learning from right handed people, he just wrote with his left hand. I use both my hands equally, but I cannot write with my left or use a mouse with my left hand. And I also have 4 step brothers, and 3 of them are right handed.

With left handed people their hemispheres(sp?) of the brain isn't switched around, the layout and everything is the same as right handed people.

[Idobox]

The brain is not symmetrical, and has a dominant hemisphere.

It's still a bit of a mystery why certain parts are symmetrical and others not, and what makes an hemisphere dominate the other. It could be genetic, environmental or behavioural factors that decide it.

Brocca's area, for example, is on the dominant hemisphere, which means it's not on the same side for right and left handed people.

I think we have developed this asymmetry as a smart way to manage brain resources. Throwing stuff used to be critical for survival, and we are insanely good at it. This suggest a significant part of our brain is dedicated to that task. On the other hand (ha ha), if you are already able to throw stuff with great accuracy from your right hand, it's not very important to be able to do it from the left hand too, so the most efficient use of your brain capacity is to invest more on one side. You can then either let the other side underdeveloped and save energy, or use it for other tasks (more likely).

[lajoswinkler]

The argument about the ink and the writing is faulty. There are cultures where the direction of writing was from right to left. There are cultures where it's from up towards down.

There were even cultures where the direction was shifted with each new line.

The cause might not be dominantly genetic or environmental, but epigenetic. We simply don't know yet.

[Mr Shifty]

To add on, Egyptian, the second oldest writing system we know of, was mostly written right-to-left, though sometimes in other directions determined by the layout of the sheet or tablet being used. Phoenician and all the writing systems derived from it or related to it (Hebrew, Arabic, Ancient Greek) were written right-to-left. The Indus script (Harrapan) was mostly written right-to-left. In short, there is no clear bias for left-to-right writing in ancient scripts.

EDIT: We know for sure that handedness is polygenic, involving at least 40 genes in a complex weave of environmental and genetic interactions. Read any book about evolutionary developmental biology and you'll find that gene-to-phenotype is a long, twisty, complex road with many branches and crossings and interactions. It's sort of silly to try to divide phenotypic effects into genetic and environmental camps because genetic expression is affected by the embryo's environment and vice versa. It's quite possible that handedness is simply a by-product of selection for some other trait and serves no evolutionary purpose at all.

Edited October 18, 2013 by Mr Shifty

[Idobox]

We know for sure that handedness is polygenic, involving at least 40 genes in a complex weave of environmental and genetic interactions. Read any book about evolutionary developmental biology and you'll find that gene-to-phenotype is a long, twisty, complex road with many branches and crossings and interactions. It's sort of silly to try to divide phenotypic effects into genetic and environmental camps because genetic expression is affected by the embryo's environment and vice versa. It's quite possible that handedness is simply a by-product of selection for some other trait and serves no evolutionary purpose at all.

It's nice to see posts by people who know what they're talking about.

That being said, I disagree on the usefulness of dividing phenotypic effects into genetic and environmental. Some phenotypes are clearly commanded by genetics, such as eye colour, while others are clearly caused by environment and behaviour, like deformities caused by teratogens or repeated activities. Of course, there are lots of traits that are a combination, and we're used to the terms genetic predisposition and risk factor.

[Ruinsage]

Right handed master race

[MC.STEEL]

I would trow in a conspiracy theory or two but not everyone likes that so my (slightly) more sensible explanation is...

is in the human brain and how it is structured,dont realy want to go in dept of it.

[Pds314]

Right handedness could also stem from some very low-level details of the biology, or even physics.

At the very lowest level, Neutrinos and some other particles don't have rotational symmetry, having different masses if they have a reversed spin. This could make for very different results when interacting with other matter

This may be true of other more relevant particles as well.

On a more likely level, biology is inherently handed and cannot function with mirrored versions of itself. In fact, DNA, Amino Acids, sugars, etc are all handed. If we meet aliens, there is a good chance that they will, even under the unlikely chance that they look like us and barring physical laws governing the natural generation of mirrored life-forms, will actually be mirrored versions of what they would look like as earth life. So ~50% of alien cuisine should, no matter how good it tastes, be indigestible (the business implications for weight-loss companies are clear).

Finally, there are a couple reasons why handedness is needed in biological systems, the first being that crossing wires/nerves can't make direct contact, and therefore must go around each other in an assymetrical way, the second being that if anything develops a handedness, everything benefits from developing a handedness to interact with it.

[togfox]

Maybe we're just taught to be right handed. Or more correctly, as children we copied our parents who copied their parents who copied their parents who copied Adam - who obviously plucked the apple with his right hand. I know this because the fresco on my church wall has him using his right hand.

[lajoswinkler]

Maybe we're just taught to be right handed. Or more correctly, as children we copied our parents who copied their parents who copied their parents who copied Adam - who obviously plucked the apple with his right hand. I know this because the fresco on my church wall has him using his right hand.

Really?...

[Mr Shifty]

Maybe we're just taught to be right handed. Or more correctly, as children we copied our parents who copied their parents who copied their parents who copied Adam - who obviously plucked the apple with his right hand. I know this because the fresco on my church wall has him using his right hand.

You have won the internets with this comment:) I think I'm going to start collecting these great examples of Poe's Law.

[Khalashnikovf]

Maybe we're just taught to be right handed. Or more correctly, as children we copied our parents who copied their parents who copied their parents who copied Adam - who obviously plucked the apple with his right hand. I know this because the fresco on my church wall has him using his right hand.

Yep, you are correct sir. It is that simple. We were just taught to grab pen with our right hand because that is the way it is common. Well, at least it was common in 1968 to 1989 in Czechoslovakia. Yep, Communist forced everyone to be right handed because left handed person was crippled and useless so he would ended only on some more simple job but no high school or even college. yeah, its good to live after communist so I can be left handed

[dharak1]

Maybe handed-ness is common because as a social species it is better to be able to share handed tools. if it was 50/50 we would have a hard time sharing tools because there would be less right handed ones but more left handed ones. Only 1 in 2 people would have a tool for our handedness whereas now its 4/5.

[Dispatcher]

Because right hands were all that were left?

Personally, I'm right handed at some tasks, left handed at others, and I've taught myself how to be ambidextrous in some tasks. I think its mostly preferences based on early choices.