Why Am I Left-Handed?

ralferoo

> 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.

akk0

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.