Are you lefthanded?

[David Hess]

But looking at lefties from a certain age, you might think they're righties. My father is left handed but was forced to write right handed and hence has done ever since.

I do not know if this is still done but in the past in the US, left handed children were trained to be right handed.  Right handedness was enforced at an early age.

I was born right handed, like all humans, but was able to overcome that disability at an early age.

I am not sure if you are serious or just making a point but left handedness is genetic although not in the sense most people think of.  If it was purely random, then handedness should be evenly distributed.  Genetics produces an uneven distribution making most people right handed.  (1) (2)

The odd distribution of left handedness was recognized in ancient times leading to the etymology of sinister and dexter.  It also influenced architecture; stairs wind upward in a clockwise direction advantaging the defender whose right hands are free and disadvantaging the attacker whose right hands are against a wall.  The pragmatic Romans used left handed soldiers on one side of the phalanx where right handed soldiers would have been at a disadvantage.

(1) This gets tricky.  A genetically determined trait requires variation of expression, right?  There is little or no variation but does anybody doubt that 5 fingered hands are completely determined by genetics?

(2) In some snails, the direction of their spiral shells is the phenotypic expression of the *mother's* genotype.  If you were to look at the individual's genetics, no link would be found but it is still a trait controlled by genetics, just another individual's genetics.

[CJay]

But looking at lefties from a certain age, you might think they're righties. My father is left handed but was forced to write right handed and hence has done ever since.

I do not know if this is still done but in the past in the US, left handed children were trained to be right handed.  Right handedness was enforced at an early age.

My partner's father was trained to be right handed even though he was naturally left handed, it was seen as a weakness by his father.

The result is that he's ambidextrous, equally incompetent with both hands

(joke, he's a skilled woodworker and an all round good bloke)

As a child I was 'encouraged' to be right handed but that didn't last long, unfortunately back then it was very rare to find a teacher who knew how to teach a left hander how to write and as someone else has noted, using a fountain pen left handed is a guarantee of ink covered hands.

[P90]

When I was a child, I was forbidden to hang around left handed kids, in case left-handedness was contagious...

[CatalinaWOW]

I am ambidextrous, in the sense that I am clumsy with both hands.  I can do most things with either hand, though I definitely write better right handed.

[helius]

The results will be biased BTW. I would look up what the name of the bias it is...

Self-selection bias. People who share the dominant trait (right-handed) will not open the thread.

I am not sure if you are serious or just making a point but left handedness is genetic although not in the sense most people think of.  If it was purely random, then handedness should be evenly distributed.  Genetics produces an uneven distribution making most people right handed.

The heritability of handedness is somewhere below 25%.

(1) This gets tricky.  A genetically determined trait requires variation of expression, right?  There is little or no variation but does anybody doubt that 5 fingered hands are completely determined by genetics?

The point is that there is no scientific meaning to "genetically determined trait". Heritability is measured as the percentage of variability that is caused by genetic differences. When few genetic differences exist, most variability is caused by environmental differences. So the heritability of finger number is extremely low.

[David Hess]

I am not sure if you are serious or just making a point but left handedness is genetic although not in the sense most people think of.  If it was purely random, then handedness should be evenly distributed.  Genetics produces an uneven distribution making most people right handed.

The heritability of handedness is somewhere below 25%.

That research is based on phenotypic expression.  Handedness is probably just as heritable as left-right asymmetry.

The heritability of handedness or the heritability of the variation in handedness?  Something is biasing handedness massively toward people being right handed.

(1) This gets tricky.  A genetically determined trait requires variation of expression, right?  There is little or no variation but does anybody doubt that 5 fingered hands are completely determined by genetics?

The point is that there is no scientific meaning to "genetically determined trait". Heritability is measured as the percentage of variability that is caused by genetic differences. When few genetic differences exist, most variability is caused by environmental differences. So the heritability of finger number is extremely low.

That is the opposite though.  The heritability of finger number is extremely high despite little variation and environmental differences have a puny effect.  That is why this is so tricky.

https://en.wikipedia.org/wiki/Heritability

A prerequisite for heritability analyses is that there is some population variation to account for. This last point highlights the fact that heritability cannot take into account the effect of factors which are invariant in the population.

[mtdoc]

I am not sure if you are serious or just making a point but left handedness is genetic although not in the sense most people think of.  If it was purely random, then handedness should be evenly distributed.  Genetics produces an uneven distribution making most people right handed.

The heritability of handedness is somewhere below 25%.

That research is based on phenotypic expression.

Huh? Handedness is a phenotypic expression.    Twin studies have shown that handedness is determined by approximately 24% genetic effects with the rest being environmental influences.

The heritability of handedness or the heritability of the variation in handedness?

?? Does not compute.

Something is biasing handedness massively toward people being right handed.

I don't think anyone knows the exact answer to that question.  The real question is why is the brain heavily lateralized?  Handedness is just one manifestation of  brain lateralization.  IOW, brain lateralization and handedness go "hand in hand" . 

There is a long and rich anthropologic research history into the evolution of human language and associated brain lateralization. There is also a long history of modern human neurology research mapping brain lateralization. 

Why the large majority of humans are left hemisphere dominant (and thus right handed) is not known. A quick search came up with this paper which gives a pretty good overview of this question and possible answers.

[helius]

That is the opposite though.  The heritability of finger number is extremely high despite little variation and environmental differences have a puny effect.  That is why this is so tricky.

You should specify if you are talking about finger number in the population or only in neonates. There are about 22,000 amputations of orthonumerary fingers every year in the US; I would think that has a greater impact on the overall number of fingers than polydactyly.
At first it may seem odd to talk about heritability of amputations from accident or disease. But since you don't a priori know what causes amputations, it makes perfect sense to study them as one more contributor to variations in phenotype. This open-mindedness is especially important when it relates to heritable differences in behavior, since they are not self-evident when the individual is born.

[Ampera]

left handed students always have ink pen stains on their left hand... LOL perhaps not as much today since everyone takes a laptop to class...

I draw primarily with my right hand, and I still have ink stains on my hand.

I also happen to use a fountain pen, so that may be part of it.

[WZOLL]

100% left handed with everything except things that con only be used right handed like guitars. I was born left handed and no one else in my family that i know of is left handed. As a student, the struggle with binders, desks, and "pencil lead hand" is very real.

[Brumby]

Who says guitars can only be used right handed?

[P90]

Who says guitars can only be used right handed?

 
I play guitar with both hands. you kind of have to. lol

[tszaboo]

The results will be biased BTW. I would look up what the name of the bias it is...

Self-selection bias. People who share the dominant trait (right-handed) will not open the thread.

Exactly, thank you. Also, the Non response bias.
https://en.wikipedia.org/wiki/Non-response_bias
Not because right handed people are unable to click on it, because they dont care to click on it.
Imagine, you make a telephone survey, and find that 90% of people who answered, tend to answer telephone surveys.

[helius]

Imagine, you make a telephone survey, and find that 90% of people who answered, tend to answer telephone surveys.

From your example, it's clearly not possible to eliminate these types of biases in the data. So what polltakers attempt to do is tracking: to sample the same population over time and see how their answers change. If you know that your data has a bias in a certain direction, you won't be interested so much in the absolute results, but the differential can still be useful. It's harder to do this with online polls because of the times people vote not being recorded, and the change in views over time obscuring any underlying variation.

[retrolefty]

Imagine, you make a telephone survey, and find that 90% of people who answered, tend to answer telephone surveys.

From your example, it's clearly not possible to eliminate these types of biases in the data. So what polltakers attempt to do is tracking: to sample the same population over time and see how their answers change. If you know that your data has a bias in a certain direction, you won't be interested so much in the absolute results, but the differential can still be useful. It's harder to do this with online polls because of the times people vote not being recorded, and the change in views over time obscuring any underlying variation.

 The 'polls' run here are far from statistically valid for many reasons, sample size alone. However the results so far are pretty weird. True Ambidexter people represent only 1% of the general population, so over represented here (11%) or just not 'True' Ambidexter, but rather useful with either so they voted that way? And of course the left handed vote is higher then 10%.

 I guess I should have used the name left dominant in the poll question rather then left handed, as one who is truly left dominate will usually have better vision left Vs right eye, foot size slightly larger, hearing better, etc. There is truly a genetic difference that environment could have no bearing on. An example of environment effect is I am lefty all the way, but as a youth I could only play around with golf using right handed clubs (nobody around had lefty clubs), so that is what I 'learned' on, and to this day a left handed club does not feel correct and I continued to use right handed clubs, a matter of having to first 'unlearn' first. That is an environmental effect, not genetic.
 

Self-selection bias. People who share the dominant trait (right-handed) will not open the thread.

Well the majority of poll voting responses are right handed, so that statement seems wrong or misstated?

Lefty

[mtdoc]

Self-selection bias. People who share the dominant trait (right-handed) will not open the thread.

Well the majority of poll voting responses are right handed, so that statement seems wrong or misstated?

True.  It should be "People who share the dominant trait (right-handed) are less likely to open the thread."

Which will of course skew the results.

[retrolefty]

Self-selection bias. People who share the dominant trait (right-handed) will not open the thread.

Well the majority of poll voting responses are right handed, so that statement seems wrong or misstated?

True.  It should be "People who share the dominant trait (right-handed) are less likely to open the thread."

Which will of course skew the results.

 Well I guess it's just a case that you can lead a horse to water but you can't make it vote.   

[jitter]

Who says guitars can only be used right handed?

I tried to play the guitar but missed the stamina to keep going. What I found curious was that the left hand (as a righty) has to do all the difficult work, but I wouldn't dream of playing the guitar left handed...

However, I do know there are left handers who choose to play right handed, e.g. Mark Knopfler. But Paul McCartney tried to play right handed and found his progress wass not very good and switched to playing left handed. Ringo is the other lefty, however playing a right handed drum kit.

I also always wondered about right hand drive countries and changing gears in a manual gearbox...