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Most of you here will be right or left handed. A few might be ambidextrous. But were we born that way?

I'm wondering if everyone was born ambidextrous, but as they grew up became more dependent on one hand, and that hand after more use now has stronger muscles, bones etc. Or were we naturally born with one hand stronger than the other?

I've heard somewhere that it has something to do with the brain, and which side which hemisphere is on. Not sure the validity of this statement. It's also been pointed out that chimps and apes show handedness, so this probably not just a human thing.

So, are we naturally born right or left handed? Or are we all born ambidextrous and does left or right handedness develops later?

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  • $\begingroup$ Not sure what tags apply here... $\endgroup$ – Beastly Gerbil Dec 1 '16 at 19:23
  • $\begingroup$ When reading up on the subject on the internet, left handedness is described as a preference, as if it were a choice... However, I found this article, which suggests that it is factors such as environment, genetics and chance ghr.nlm.nih.gov/primer/traits/handedness $\endgroup$ – user27740 Dec 1 '16 at 19:48
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    $\begingroup$ well chimps and gorilla show handedness, take that for consideration. $\endgroup$ – John Dec 1 '16 at 21:11
  • $\begingroup$ Good question. I think the fact most people are right-handed suggests a genetic mechanism. Otherwise the choice should be random, and I would expect left/right to be equally common. This article might be a starting point: scientificamerican.com/article/why-are-more-people-right $\endgroup$ – Roland Dec 2 '16 at 7:37
  • $\begingroup$ I think you are born left or right handed and I think the following experiment 'proves' it. In the Netherlands in the 1950s (and probably many other countries), left handedness was considered bad at schools they 'taught' children to be right handed. They all had to write with their right hand. It didn't help, left handed children remained left handed. Some still write with there right hand, but do everything else with their left hand. $\endgroup$ – RHA Dec 2 '16 at 20:09
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tl;dr

Yes!

Is handedness determined before birth?

Without thinking of whether handedness is genetically or environmentally defined (see below), is handedness decided before birth?

Hepper et al. 1991 and DeVries et al. 2001 show that handedness can be inferred from from fetal position and hand usage. Typically, looking at what thumb is used for sucking is good indication of handedness.

Is handedness heritable?

The question

[A]re we naturally born right or left handed?

can sometimes be understood as

Is handedness genetically determined?

or in more concrete terms as

Is handedness heritable in humans?

If it is not obvious to you that this is your question, then you probably don't understand the concept of heritability! Then you should have a look at Why is a heritability coefficient not an index of how “genetic” something is? first and then come back here to read the results.

There have been a large number of studies on the question, unfortunately most of them were very small studies with small sample size. Medland et al. 2008 is pretty large scale twin study which report a heritability of 0.24.

In other words, yes handedness is heritable. To be more accurate, 24% of the total variance in handedness is explain by additive genetic variance. Yet again in other words.

The cooperation-competition hypothesis

On the evolution of the handedness in he human population you might want to hear about the cooperation-competition hypothesis. For that, you should have a look at this TED-ed video. As you watch this video, you'll probably be interested in reading the wikipedia article on frequency-dependent selection.

Thanks to @Mockingbird for pointing out to this video.

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    $\begingroup$ I understand heritability but that wasn't really my question. Sure, I get that you an inherit the handedness of your parents, but as your answer shows, this doesn't happen very often. I'm asking whether or not we are born with the hand we use most often, or whether we aren't born with a particular handedness and it develops over time. $\endgroup$ – Beastly Gerbil Jul 1 '17 at 10:32
  • $\begingroup$ Ted-Ed has an interestjng video on this subject. $\endgroup$ – Mockingbird Jul 1 '17 at 14:25
  • $\begingroup$ @BeastlyGerbil I understand. Please see edit. $\endgroup$ – Remi.b Jul 1 '17 at 22:50
  • $\begingroup$ Ah that's a lot better. Thanks. The hand used for sucking a thumb is a particularly interesting point... $\endgroup$ – Beastly Gerbil Jul 2 '17 at 9:22

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