Why Am I Left-Handed?

https://www.quantamagazine.org/why-am-i-left-handed-20260713/

by Brajeshwar • 9 days ago

14 3 9 days ago

ralferoo• 9 days ago

Left-handedness does not seem to be purely genetic. Two left-handed parents have a left-handed child only 25% to 30% of the time. If one identical twin is left-handed, there’s only a 20% to 30% chance the other is too. This suggests a genetic component alongside some developmental randomness.

It seems that 20-30% is double or triple the likelihood of the being lefthanded normally, implying that actually there is a stronger correlation towards genes being a factor.

If at least one of the twins was left-handed, we would expect odds of 19% among sets of twins compared to 10% among babies generally, but then expect only 1% odds of twins, both twins would be left-handed if there was no correlation. So, the expected odds of exactly one being lefthanded is then 1:19, or just over 5%. Having actual odds of this being 20-30% shows that whatever is causing this is likely to affect both babies the same.

Having said that, I don't necessarily think we can just jump to genes - it could also be due to something environmental during pregnancy, after all both babies are growing in the same environment.

akk02• 9 days ago

The article searches hard for an evolutionary explanation for why right-handedness specifically would be favored, but I think it suffices to find a reason for most people to have the same handedness, and then right-or-left can just be a coinflip. Most people having the same handedness does seem "better". Author stays by retelling a learning challenge they had as a child because of opposite handedness, I think that general idea for instance would generalize to the ancestral environment.

akk02• 9 days ago

Another example: my partner is left-handed, I am right-handed. We dabble in instruments together; we have a right-handed bass guitar, and an electronic drum kit we set up in a traditionally left-handed way. Both very doable, but there's definitely a debuff when learning from someone else. We're very monkey see monkey do.

I think the "sharp weapon" hypothesis is interesting and favors "why right and not left?" but I think it's too specific and unnecessary to explain the more important "why 90-10?".

Why Am I Left-Handed?

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