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Old 07-19-2013, 01:41 AM
panaccione panaccione is offline
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Why are people usually right handed?

as opposed to being left handed? or even ambidextrous? (wouldn't that make more sense anyway?)

I have a feeling it has something to do with the heart being positioned on the left side of our body and people naturally evolved to be right handed in order to protect that organ. But, that is just pure speculation with no basis at all.
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Old 07-19-2013, 01:48 AM
Dana Scully Dana Scully is offline
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I don't know why hoomins have handed-ness but cats have it too (I asked my vet). I scrutinized my cat at home and sure enough, he seems to be right-pawed.
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Old 07-19-2013, 06:24 AM
njtt njtt is offline
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I believe the only correct answer to this is that nobody knows. Explanations in terms of other bodily asymmetries, such as the heart, or the "dominant" brain hemisphere being on the left, are, at best, begging the question. Why are the heart and the dominant brain hemisphere normally on the left? We don't know. But even if we did know, we do not really know whether or how it would influence actual handedness. Some left-handers have their dominant brain hemisphere on the right, but not all by any means.

Possibly it all comes down, ultimately, to the chirality of biological molecules, but we have absolutely no idea why the fact that (for instance) the amino acids in proteins are in the L rather than the D form should lead (mostly, but not always - left-handers still have L amino acids) to people being right handed. Come to that, we do not really have much idea why the chirality of amino acids and other biological molecules should not be the opposite of what it is. So long as they make a consistent choice, there seems to be no very good reason why amino acids in proteins should not be in the D form rather than the L. It may well just be due to some random fluke in the very early history of the evolution of life.

Last edited by njtt; 07-19-2013 at 06:27 AM.
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Old 07-19-2013, 07:37 AM
aNewLeaf aNewLeaf is offline
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I don't know why hoomins have handed-ness but cats have it too (I asked my vet). I scrutinized my cat at home and sure enough, he seems to be right-pawed.
Agreed, one of my favorite cats was a distinct lefty.
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Old 07-19-2013, 08:20 AM
Ludovic Ludovic is online now
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I think that handedness may confer advantages in that you can become really good at some things rather than having to learn every task with both hands. If that is true (and it may or may not be,) then most people being right handed may be a random accident brought out by the advantages of being handed.
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Old 07-19-2013, 08:25 AM
njtt njtt is offline
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I think that handedness may confer advantages in that you can become really good at some things rather than having to learn every task with both hands. If that is true (and it may or may not be,) then most people being right handed may be a random accident brought out by the advantages of being handed.
Why wouldn't it be randomly 50/50?
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Old 07-19-2013, 08:56 AM
Hari Seldon Hari Seldon is offline
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Why wouldn't it be randomly 50/50?
It could be 50-50, but didn't happen to be. Suppose it started out with a slight predominance of right-handers. Then there might have been selective advantages to being right-handed. Nowadays, there is almost certainly an advantage since the world is made for right-handers. But how it got started is a mystery.

Apparently, nearly all women hold their infants with the left hand. Right-handers explain that this leaves their right hand free. Left-handers explain that they do it because they are left handed. This illustrates the difficulty of studying this kind of question.
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Old 07-19-2013, 09:12 AM
Leaffan Leaffan is offline
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It could be 50-50, but didn't happen to be. Suppose it started out with a slight predominance of right-handers. Then there might have been selective advantages to being right-handed. Nowadays, there is almost certainly an advantage since the world is made for right-handers.
Yeah, but your dominant hand is predisposed long before you start using it on power tools and scissors.

I can't imagine natural selection has favoured righties in any way; it doesn't make sense. There must be something about right-handedness that is genetically encoded.
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Old 07-19-2013, 10:12 AM
jtur88 jtur88 is offline
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The question is akin to the one about driving vehices on the right or the left. Each closed culture decided that driving on one agreed-upon side was better than letting everyone drive where they pleased. The choice of which side could have arisen from, for example, which side of the road had a dangerous dropoff when going downhill and under less control. Once a side was chosen, it just kept gaining dominance until it was regarded as "correct", and objectors were thrown into the volcano, which had a disadvantage in terms of survival.

Handedness could have gone through a similar evolution of selection, in which minority-handed people were discriminated against, which by itself would incrementally keep intensifying the preference for a culturally-approved handedness.

In the northern hemisphere, where most humans and other terrestrial species evolved, the sun and the stars move across the sky from left to right. This would be a highly visible and conspicuous right/left distinction that would be shared in common by all species, and might account for why all animals evolved the same handedness. Exactly how it would contribute to handedness would only be wildly conjectural, but suffice it to say that all animals under the northern sun observe all astronomical motion as a left-to-right phenomenon, thus being aware of their bilateral existence in the same way, in synchronization with each other.

Last edited by jtur88; 07-19-2013 at 10:13 AM.
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Old 07-19-2013, 10:26 AM
Great Antibob Great Antibob is offline
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The question is akin to the one about driving vehices on the right or the left. Each closed culture decided that driving on one agreed-upon side was better than letting everyone drive where they pleased.
Something a bit longer on facts and logic.
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Old 07-19-2013, 10:53 AM
Blaster Master Blaster Master is offline
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Yeah, but your dominant hand is predisposed long before you start using it on power tools and scissors.

I can't imagine natural selection has favoured righties in any way; it doesn't make sense. There must be something about right-handedness that is genetically encoded.
Handedness, in general, confers an advantage. As someone touched on upthread, it's better to focus on being really good with one hand than it does to be good with the same task with both hands. This pretty much explains why ambidextrousness is rare, and even those who are equally good at some tasks with both hands probably aren't equally good at other tasks with both hands.

As for why it is right-handed rather than left that is most common, I'd suggest it's probably just a genetic and social accident, it was bound to be one or the other and right was the one that won. That is, I'd imagine handedness very well could have started out fairly even, but all it takes is a small nudge in one direction or the other early on in our use of tools and our development as a society to push it in a particular direction. Imagine, the first man who develops a tool just happens to learn to use it with his right hand, gets good at it, teaches others to do it like he did, and people who become more proficient with certain tools tend to gain more status and have more offspring. But if the same man had picked it up with his left, we may very well all be left-handed today instead.

I would also imagine this effect would become more pronounced when it came to weapons, for combat, for hunting. People who were more proficient would kill off their opponents and have an easier time feeding themselves. Thus, if there was some social order for being trained to use them right-handed, and there's some genetic predisposition toward one or the other, those who would have had a bit more natural skill would start to win out and spread that genetic predisposition, even if it is slight.
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Old 07-19-2013, 10:59 AM
Great Antibob Great Antibob is offline
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I would also imagine this effect would become more pronounced when it came to weapons, for combat, for hunting.
That's actually an interesting example. While on vacation in Ireland, we saw a number of castles and one thing the various tour guides pointed out was the stairs spiraled in the towers differently (clockwise or anti-clockwise).

Apparently, this was determined by the handed-ness of the castle's owner/builder, who would naturally be more comfortable fighting with the dominant hand while retreating up a tower. They said young nobles were trained to fight with both hands but naturally the strong hand would be the better and preferred one.
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Old 07-19-2013, 11:03 AM
BigT BigT is offline
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I can't imagine natural selection has favoured righties in any way; it doesn't make sense. There must be something about right-handedness that is genetically encoded.
Huh? Not only are these not mutually exclusive, but that's how natural selection works. It changes a species' genetic makeup via having those with undesirable genetics die out.

Last edited by BigT; 07-19-2013 at 11:04 AM.
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Old 07-19-2013, 11:05 AM
Shark Sandwich Shark Sandwich is online now
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My mother tells stories about how she showed a preference to left-handedness in school, and the nuns "coaxed" her into being right-handed. Not sure how true that is, but she's right handed today.

Is there really anyone who is truly ambidextrous? Not someone who is say, right-handed but CAN do stuff left-handed, but someone who shows no preference to either hand?

I'm a lefty in that I write and eat left-handed, but I play golf, throw, and do just about everything else as a righty.
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Old 07-19-2013, 11:09 AM
jtur88 jtur88 is offline
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I went to a lot of baseball games in the Nicaraguan Major League, and I noticed that it was very rare for either a pitcher or a batter to be left-handed. Some teams had no lefties at all. I asked my Nicaraguan friend about that, and he offered a speculation. Every kid in Nicaragua, at some time in his young life, works in a sugar cane field. Nobody wants to be a a cane field with a worker who is swinging a machete left handed, so every kid has to learn to cut cane with a machete right-handed, which at least becomes the dominant hand for that kind of motion.

Marvin Benard, who was a Nicaraguan lefty, made it to the American Major Leagues, even though a lefty. It is possible that, among all the right handers in Nicaragua, being left-handed conferred a certain advantage on a player (always facing right hand pitchers, for example), so the simple fact that Benard was left handed might be what made him outstanding enough to attract major league scouts.

A disproportionately large number of major league pitchers are left-handed (about 25%) for the selective reason that a LH pitcher is harder for a LH batter to hit, because of the natural trajectory of the thrown ball. Oddly, about a quarter of all right handed people (and major leaguers) have a tendency to swing a baseball bat in what is known as a left-handed swing, thus creating a need for that many LH pitchers.
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Old 07-19-2013, 11:09 AM
TriPolar TriPolar is online now
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First answer the question "Why is there handedness?"

Then come up with some explanation of why right handedness is more common.
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Old 07-19-2013, 11:37 AM
Leaffan Leaffan is offline
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Is there really anyone who is truly ambidextrous? Not someone who is say, right-handed but CAN do stuff left-handed, but someone who shows no preference to either hand?
I'd give my right arm to be ambidextrous.
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Old 07-19-2013, 11:53 AM
PlainJain PlainJain is offline
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I have a feeling it has something to do with the heart being positioned on the left side of our body and people naturally evolved to be right handed in order to protect that organ. But, that is just pure speculation with no basis at all.
I always thought the heart was in the center.
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Old 07-19-2013, 11:55 AM
Cheshire Human Cheshire Human is offline
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I don't know why hoomins have handed-ness but cats have it too (I asked my vet). I scrutinized my cat at home and sure enough, he seems to be right-pawed.
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Originally Posted by aNewLeaf View Post
Agreed, one of my favorite cats was a distinct lefty.
I had both, once, and they used to play in an open faced cabinet I kept my magazines in by one getting inside and the other outside with the wall between them and they'd bat at each other around the wall. But their preferred inside/outside positions were the opposite of their preferred paw. It was funny to watch them each reaching around awkwardly wrong-pawed to bat at the other.

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Is there really anyone who is truly ambidextrous? Not someone who is say, right-handed but CAN do stuff left-handed, but someone who shows no preference to either hand?
Yes, I've known a (very) few. I'm kinda close, in that which way I first learned it is the way I do it, and I have to ask someone who knows which handed I'm doing it. I also do many things either way, just as well. I just have to take a little extra effort to learn the other way, too.
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Old 07-19-2013, 11:56 AM
Tastes of Chocolate Tastes of Chocolate is offline
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In the northern hemisphere, where most humans and other terrestrial species evolved, the sun and the stars move across the sky from left to right. This would be a highly visible and conspicuous right/left distinction that would be shared in common by all species, and might account for why all animals evolved the same handedness. Exactly how it would contribute to handedness would only be wildly conjectural, but suffice it to say that all animals under the northern sun observe all astronomical motion as a left-to-right phenomenon, thus being aware of their bilateral existence in the same way, in synchronization with each other.
Huh? Your theory only works if all animals were always facing the same direction. The first one to face north instead of south would throw your theory off. I've always lived in the northern hemisphere, and I was required under pain of dead (because otherwise I'd tell you the whole idea is silly) I'd say the sun rises on the right and sets on the left. I'm sure that's a result of reading maps with North on the top.
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Old 07-19-2013, 01:08 PM
Duckster Duckster is offline
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as opposed to being left handed? or even ambidextrous? (wouldn't that make more sense anyway?)

I have a feeling it has something to do with the heart being positioned on the left side of our body and people naturally evolved to be right handed in order to protect that organ. But, that is just pure speculation with no basis at all.
Only a right-hander would have to ask such questions. Us true Lefties not already know the answers but knew you were going to ask the questions in the first place. We tolerate this Ad nauseam because it amuses us.

BTW, it has nothing to do with the physical position of the heart.
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Old 07-19-2013, 05:51 PM
Lynn Bodoni Lynn Bodoni is offline
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My mother tells stories about how she showed a preference to left-handedness in school, and the nuns "coaxed" her into being right-handed. Not sure how true that is, but she's right handed today.
At least as late as the 1980s, I met people who thought that I should force my left handed daughter to write and eat with her right hand. I refused to this. She learned to use scissors and a mouse right handed, even though I bought her lefty scissors.

My maternal grandfather was left handed, and the teachers (regular public school teachers) tied his left arm to his body in school, so he sort of learned how to write with his right hand. Then he broke his right arm, and they had to let him write with his left hand. He always claimed that this was why his handwriting was so bad.
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Old 07-19-2013, 06:00 PM
Cheshire Human Cheshire Human is offline
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We tolerate this Ad nauseam because it amuses us.
You 'handed' people amuse us ambis even more. I'll take on any of you 'handed' people, any time. Magic markers at twenty paces. The winner is the first who can write a number '6' top-side up, and proper right-left orientation on the other's right and left cheeks wins.
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Old 07-19-2013, 07:59 PM
panaccione panaccione is offline
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My maternal grandfather was left handed, and the teachers (regular public school teachers) tied his left arm to his body in school, so he sort of learned how to write with his right hand.
What could possibly make them think this was a good idea?
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Old 07-19-2013, 08:20 PM
Northern Piper Northern Piper is online now
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Is there really anyone who is truly ambidextrous? Not someone who is say, right-handed but CAN do stuff left-handed, but someone who shows no preference to either hand?
President Garfield was.

He could write in Greek with one hand, and in Latin with the other hand, at the same time!
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Old 07-19-2013, 08:32 PM
Leaffan Leaffan is offline
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What could possibly make them think this was a good idea?
Because in ye olden days no one believed in a genetic preference for handedness, and since righties were the majority, all kids were forced into learning to write with their right hand.

It sounds quite bizarre; in fact it sounds like how we treated sexual preference until very recently.

Wow. I'd never connected the two before, but that's exactly what it is. "You can't favour your left hand! That's not moral or correct. You must favour your right hand! I'll teach you to be right-handed!"
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Old 07-19-2013, 09:32 PM
Northern Piper Northern Piper is online now
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As to the question "why handedness?", I would argue, based on my own personal experience, that handedness confers a definite evolutionary advantage.

I'm right handed, but cross-dominant - that is, for certain things, I prefer my left hand.

The problem is, that requires increased decision-making time.

When I'm cooking, the cross-dominant really comes out - there's a lot of things where I have to stop and think which hand to use, or I have to experiment to see which is better. For instance, when I'm peeling carrots, it just feels better to hold the carrot in my right hand, and use the peeler in my left. But then it's time to cut the carrots, and it just feels better to hold the carrot in my left hand, and use the right hand to hold the knife.

So what? Well, lat's think about caveman Piper and his buddy Thag. Thag sees a saber-toothed tiger coming and, being strongly handed, grabs his spear with his favoured hand to defend himself.

Caveman Piper pauses and thinks, "Hmm, spear against sabre-tooth. Righthand or left hand? Which feels better? Let me experiment ..."

Sabre-tooth tiger: "hmm - one guy with a pointy stick at the ready; one guy switching it back and forth ... Ka-runch!"

Similarly, I have trouble telling my right from my left - something that other cross-dominants on this board have mentioned in previous threads.

So when I'm driving and Mrs Piper says "Turn left", and I think, "left - which is left again?" I just sail through the intersection.

So what? Well, when Thag yells, "Caveman Piper - sabre-tooth on your left!"

And Caveman Piper thinks, "left - which I left, again?"

And sabre-tooth again thinks, "one guy with a pointy stick aimed at me, another guy looking at his hands: Ka-runch!"

Last edited by Northern Piper; 07-19-2013 at 09:32 PM.
  #28  
Old 07-19-2013, 09:39 PM
Dr. Strangelove Dr. Strangelove is offline
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Anyone know if people with situs inversus are more likely be left-handed?
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Old 07-19-2013, 09:54 PM
Leaffan Leaffan is offline
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As to the question "why handedness?", I would argue, based on my own personal experience, that handedness confers a definite evolutionary advantage.
.....
Ya but that doesn't explain why left handed people are so underrepresented; it may explain why pseudo-ambidextrous people who suffer from a moment's confusion are though.

Wikipedia
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Globally, roughly 12% of men and 10% of women are left-handed.
This correlates with homosexuality rates, doesn't it? Hey, I'm no expert and I'm not drawing conclusions, but it seems to me that there must be, and always have been, genetic predispositions involved in both of these somewhat abnormal conditions.
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Old 07-19-2013, 09:55 PM
Really Not All That Bright Really Not All That Bright is offline
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Anyone know if people with situs inversus are more likely be left-handed?
They're not.

Last edited by Really Not All That Bright; 07-19-2013 at 09:55 PM.
  #31  
Old 07-19-2013, 10:55 PM
Northern Piper Northern Piper is online now
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Ya but that doesn't explain why left handed people are so underrepresented; it may explain why pseudo-ambidextrous people who suffer from a moment's confusion are though.
I wasn't saying it was. As the opening line of my post indicates, I was just commenting on "why handedness?", not why there is a general preference for a particular hand.
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Old 07-19-2013, 11:41 PM
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It might be that right-handedness doesn't confer any evoluntionary advantage, but rather it's genetically linked to a trait that does.

There's research showing that both left-handed and ambidextrous people tend to have certain neurological abnormalities than the right-handed. Autism, schizophrenia, dyslexia, and ADHD are disproportionately represented among left-handers. Both geniuses and mentally handicapped people are also more likely to be left-handed.

The left hemisphere is where most people base their language functioning, both right and left-handed people. But for some reason left-handed people are more likely to have less lateralization, which may make them more physically clumsy and less "smooth tongued". It's no surprise that the athletic eloquent fellow is more likely to pass on his genes than the stammering klutz.

So it's probably not that right-handedness is so desirable that it alone wins the evolutionary contest. It's just that it's a sign that, for whatever reason, the brain is laid out in a "desirable" way. But as humans become more reliant on technology, the more "geeky" traits associated with left-handed people may give people more "fitness". And the nerds shall inherit the earth.
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Old 07-20-2013, 02:52 AM
Lynn Bodoni Lynn Bodoni is offline
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Because in ye olden days no one believed in a genetic preference for handedness, and since righties were the majority, all kids were forced into learning to write with their right hand.

It sounds quite bizarre; in fact it sounds like how we treated sexual preference until very recently.

Wow. I'd never connected the two before, but that's exactly what it is. "You can't favour your left hand! That's not moral or correct. You must favour your right hand! I'll teach you to be right-handed!"
That was pretty much it. Lefthandedness was also linked to being evil in general, and a sign that a person was wicked. A child with a strong preference for using his/her left hand was considered to be headstrong and disobedient at the very least, and my old boss thought that being lefthanded led to devil worship. Of course, she also thought a lot of other things led to devil worship. If she'd known that I had not one but TWO black cats when she'd interviewed me, I never would have been hired.
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Old 07-20-2013, 03:33 AM
Sleel Sleel is offline
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Handedness is one byproduct of brain lateralization. We still don't really know why lateralization became prevalent, but it seems to confer some advantages for separate processing. One reason why lefties are supposed to be more creative is that they tend to have less strongly lateralized brains, so they come up with connections between disparate ideas more easily. High intelligence also seems to be lightly correlated with left-handedness.

There's a pretty good chunk of The Language Instinct and How the Mind Works, both by Steven Pinker, that discuss lateralization, particularly the connection with language. Those are probably the most approachable, yet scientific books I've read on the subject.

Handedness is actually a continuum, with few people being totally right- or left-dominant. Some degree of mixed body dominance is common. You might have someone who is strongly right-handed, but strongly left-eyed and weakly left-footed, like a friend of mine I taught to shoot better. You should shoot based on eye dominance, not hand dominance; target acquisition and aiming are the most important things. It took some work to get him using his left hand, but his accuracy and speed went way up afterward.

While there is no single "left handed" gene, there are some genetic factors; handedness can run in families. But environment seems to be a stronger selector. Stressful conditions at conception and birth have an effect on the prevalence of left-handedness.

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I would also imagine this effect would become more pronounced when it came to weapons, for combat, for hunting. People who were more proficient would kill off their opponents and have an easier time feeding themselves. Thus, if there was some social order for being trained to use them right-handed, and there's some genetic predisposition toward one or the other, those who would have had a bit more natural skill would start to win out and spread that genetic predisposition, even if it is slight.
Actually, violence selects for more lefties. In other words, the minority preference confers an advantage in combat. Either that, or left handed people are naturally more violent

(Full disclosure: I'm left handed. You got a problem with that?!)

From some of my anthropology reading I remember that the Yanomami have something like 20% incidence of left-handedness. "Fierce" men, who go on more raids and are more willing to undergo inter-tribal duels, have more wives than men who show less aggression, and these men are more likely to be left handed. (In duels they beat each other over the head with really long wooden poles, deliberately receiving head wounds to show how tough they are; this is not dissimilar to Heidelberg dueling).
  #35  
Old 07-20-2013, 03:35 AM
Johanna Johanna is offline
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Huh? Your theory only works if all animals were always facing the same direction. The first one to face north instead of south would throw your theory off. I've always lived in the northern hemisphere, and I was required under pain of dead (because otherwise I'd tell you the whole idea is silly) I'd say the sun rises on the right and sets on the left. I'm sure that's a result of reading maps with North on the top.
No—that isn't what jtur88 meant. For observers in the Northern Hemisphere, due to the Earth's rotation, you see the Sun, Moon, and all the planets and stars going around the sky from left to right, regardless of which direction you're facing.

Face south, and you'll see the Sun (and everything else up there) rising on your left hand and setting on your right hand, moving from left to right in front of you.

Face north, and the Sun rises on your right hand and sets on your left hand, going behind you where you can't see it. If you face north at the summer solstice, you'll be able to observe the sunrise in the northeast and sunset in the northwest, and from what you can see of it facing north and turning your gaze toward northeast at sunrise and northwest at sunset, relative to the azimuth of your line of sight, it still goes left to right.

In the Northern Hemisphere, the only way to see things going from right to left would be if you had an extra pair of eyes in the back of your head, while still perceiving your left and right hands from the viewpoint of your eyes in the front of your head.

Last edited by Johanna; 07-20-2013 at 03:39 AM.
  #36  
Old 07-20-2013, 09:54 AM
Chronos Chronos is offline
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There are three questions here, not one. First, why do individuals have handedness? That's fairly easy: It's because being really good with one hand and lousy with the other is usually more useful than being sort of good with both. Northern Piper illustrates this well.

Second, why does handedness tend to be uniform within a species? The use of tools in humans may well be part of it, and humans do seem to have a larger bias than most animals, but many non-tool-using animals also seem to have a species-wide predisposition to one side, so there must be some reason for that.

Third, given a species-wide predisposition to one side or the other, why does a particular species have the predisposition it does? That one is probably just down to random chance.
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Old 07-20-2013, 10:18 AM
jtur88 jtur88 is offline
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Originally Posted by Tastes of Chocolate View Post
Huh? Your theory only works if all animals were always facing the same direction. The first one to face north instead of south would throw your theory off. I've always lived in the northern hemisphere, and I was required under pain of dead (because otherwise I'd tell you the whole idea is silly) I'd say the sun rises on the right and sets on the left. I'm sure that's a result of reading maps with North on the top.
About 90% of the inhabitable land mass of the earth, and 90% of its zoofauna, occupy the northern hemisphere and look south at the sun and see it go from left to right. As for reading maps, I'm quite certain that genetic handedness predated the convention of placing north at the tops of maps.

Last edited by jtur88; 07-20-2013 at 10:20 AM.
  #38  
Old 07-20-2013, 01:07 PM
Leaffan Leaffan is offline
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Huh? Not only are these not mutually exclusive, but that's how natural selection works. It changes a species' genetic makeup via having those with undesirable genetics die out.
Sure, so tell me: What is undesirable about being left-handed? Why would lefties be naturally selected out of the gene pool? They wouldn't.
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Old 07-20-2013, 01:39 PM
Chronos Chronos is offline
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They would if they were surrounded by righties, who made and used tools that were awkward for a leftie to use. Or if their righty brethren decided that the minority must be religiously persecuted. Or if there's some factor external to humanity (the course of the Sun through the sky?) that somehow inherently disfavors lefties.
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Old 07-20-2013, 01:48 PM
Leaffan Leaffan is offline
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Unconvincing.
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Old 07-21-2013, 05:17 AM
si_blakely si_blakely is offline
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It is just worth noting that in some combat disciplines (fencing, for example), left-handedness is an advantage. Fighting a cross-handed opponent is very different to a same-handed one. The angles and attacks are not the same as a similar handed opponent.
Right handed fencers train and fight with more right-handers at the lower levels (due to the distribution of handedness). Left handed fencers have to train mostly with right-handers, too. So lefthanders are expected to fight cross-handed, but for many right handers, it is more difficult, due to lack of practice. So lefthanders can beat right handers just due to this inexperience. At higher levels in the sport, the ratio of lefthanders is much higher than in the general population, and the exposure level to cross and straight handedness goes up for both left and right handed participants, so the advantage diminishes.
This occurs in other sports, too. Cricket, boxing, tennis, all confer some advantage to the lefthanded at the lower levels due to the novelty factor, and increase the percentage of left handed players at the top levels.
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Old 07-21-2013, 06:04 AM
Nava Nava is offline
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I always thought the heart was in the center.
Not really, it's center-left. The right lung is bigger than the left lung and has three lobes to the left's two.

"Human beings have bilateral symmetry" is a gross oversimplification and falls down the wayside as soon as you cut one's torso open.

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Sure, so tell me: What is undesirable about being left-handed? Why would lefties be naturally selected out of the gene pool? They wouldn't.
Picture a society (say, Sparta or early Rome) where fighting is done in formation and warrior is the most prestigious profession. Someone who always starts walking on the wrong foot and who has to use weapons with his uncoordinated hand will never do as well as his mates for whom that's the good hand.

I'm lefty-forced-righty: I can't draw or write with my left hand, but if you put a tennis racket in my right hand and throw a ball at me, I'll change hands and hit the ball. Tying the racket to my hand results in not being able to hit anything except the floor when I fall on my ass. Now imagine if instead of a racket it was a sword and I had two guys a yard to the side.

Last edited by Nava; 07-21-2013 at 06:09 AM.
  #43  
Old 07-21-2013, 07:55 AM
aNewLeaf aNewLeaf is offline
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Apparently, nearly all women hold their infants with the left hand. Right-handers explain that this leaves their right hand free. Left-handers explain that they do it because they are left handed. This illustrates the difficulty of studying this kind of
question.
Fascinating. I'm a dude, but I hold babies left handed.
There's a few tasks I do left handed, like eat, but predominantly right handed.
To me, holding the baby in left leaves right hand free for feeding, adjusting, etc.

I learned to use a computer mouse on either side- I'm ambimoustrous.
  #44  
Old 07-21-2013, 07:59 AM
Manda JO Manda JO is offline
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Originally Posted by Nava View Post
Picture a society (say, Sparta or early Rome) where fighting is done in formation and warrior is the most prestigious profession. Someone who always starts walking on the wrong foot and who has to use weapons with his uncoordinated hand will never do as well as his mates for whom that's the good hand.
.
But what percentage of humanity has lived in civilizations with formation warfare? It was only developed a few thousand years ago, was never used by most cultures, and died out fairly quickly.

Furthermore, handed-ness doesn't seem to be strictly genetic, though there may well be a genetic pre-disposition. Some families have more lefties than others, but it's not like color blindness or something where you can track it.
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Old 07-21-2013, 09:58 AM
monstro monstro is online now
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Nor is handedness something that you can't unlearn/learn.

If fighting prowess was the filter by which our ancestors all had to pass through, I'm thinking there would be a lot of inheritable traits in our population that we wouldn't see as frequently as we do. Like myopia, seasonal allergies, or flat feet. I'd also expect to see an uneven distribution of left-handedness, since not every society has had pressure to be militant. I'd also expect males to be less likely, rather than more likely, to be left-handed.
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Old 07-21-2013, 10:08 AM
chinchalinchin chinchalinchin is offline
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http://www.julianjaynes.org/bicameralmind.php
  #47  
Old 07-21-2013, 10:10 AM
TriPolar TriPolar is online now
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Originally Posted by Chronos View Post
There are three questions here, not one. First, why do individuals have handedness? That's fairly easy: It's because being really good with one hand and lousy with the other is usually more useful than being sort of good with both. Northern Piper illustrates this well.
This is a popular, not to mention sensible hypothesis. It may be ties to the unique characteristics of the human brain.

Quote:
Second, why does handedness tend to be uniform within a species? The use of tools in humans may well be part of it, and humans do seem to have a larger bias than most animals, but many non-tool-using animals also seem to have a species-wide predisposition to one side, so there must be some reason for that.
That doesn't actually explain it. This part is confounding at the moment. There isn't any real good reason for it. As mentioned above there isn't a strong correlation between genetics and which handedness among species. Only when humans reached the point of making the sharp sided rock would it make a difference, the pointy stick worked with either hand.

Quote:
Third, given a species-wide predisposition to one side or the other, why does a particular species have the predisposition it does? That one is probably just down to random chance.
Well, there is no other explanation right now, so it's as good an answer as any.
  #48  
Old 07-22-2013, 06:35 PM
Chronos Chronos is offline
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That doesn't actually explain it. This part is confounding at the moment.
Which is what I said. Tool use can't entirely explain it, because cats (for instance) don't use tools, but still have a species-wide preference tendency (for the left, as it happens). So there must be something else causing pawedness in cats, and presumably that same mechanism would also be at work in humans, but we don't know what it is.
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Old 07-22-2013, 11:48 PM
chris3g chris3g is offline
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I'm not sure if someone mentioned it, but maybe it was due to the Founder effect? (Or is it bottleneck effect, i always confuse them)

For example, if say, all human have a small group of common ancestor of specie X (all the other member of the species perished), and this small group are very much related (a family lets say), and said family is genetically disposed to be right-handed.

It stands to reason that all their descendent would be genetically pre-disposed to right-handiness.

Last edited by chris3g; 07-22-2013 at 11:50 PM.
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