

Ask HN: What causes some people to be left-handed? - zvanness

Does anyone have a solid theory on why there is such an unbalanced ratio between the number of right-handed people and left-handed people. Why is the default to be right-handed? What really causes people to be left-handed?
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devfeed
I can't answer your first question about why left-handed people exist, but I
can provide some clues about the proportions:

Left-handedness is a disadvantage in society where everything is designed for
the right-handed person. However, there is one advantage to being left-handed:
in hand to hand or sword to sword combat, the southpaw has an advantage in
being unfamiliar.

This article
[http://www.economist.com/node/3471297](http://www.economist.com/node/3471297)
(Economist, 2004) describes an empirical finding: in societies that were
historically more violent, the left-handedness proportion is higher.

Perhaps this is also why left-handed people even exist. They have an advantage
in historical person-to-person violent conflicts. This advantage would go away
as their proportion gets higher. I presume (this is conjecture) that the
minority proportion that it is, is the steady state equilibrium where the
violent advantage outweights the other disadvantages of being out of sync with
society.

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jballanc
Ah! I get to plug one of my favorite websites, OMIM (Online Mendelian
Inheritance in Man): [http://www.omim.org](http://www.omim.org)

Their article on left handedness goes into great detail as to the biology
behind hand preference. In short, it's related to brain patterning and the
direction the hair on your head swirls (seriously!):
[http://omim.org/entry/139900](http://omim.org/entry/139900)

As for the evolutionary reason, the most recent research suggests that it may
have to do with cooperation. Simply put, it's easier to cooperate when
everyone (or most everyone) uses the same hand for most activities. More
details here:
[http://www.northwestern.edu/newscenter/stories/2012/04/left-...](http://www.northwestern.edu/newscenter/stories/2012/04/left-
handed-minority.html)

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draker
[http://www.reddit.com/r/askscience/comments/1j7db9/why_are_m...](http://www.reddit.com/r/askscience/comments/1j7db9/why_are_most_people_right_handed/)

Answer from an individual that studies "handedness".

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essessv
This is a question appropriate for Quora, I feel.

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wglb
This is highly anecdotal.

My uncle was born right-handed. When he was young, he broke his collarbone on
the right side. While this was healing, he used his left hand, and continued
to do so from then on.

Then, working on farm machinery, he ran his left hand through a V-belt,
injuring it badly. While that was healing, he went back to using his right
hand again.

Probably not very typical.

