[ndsipa_pomu]

From my experiences, I think it's mainly learned.

I'm right-handed, but I trained myself to use a mouse/trackball left-handed due to better ergonomics. I was getting back/shoulder pain and thought that it was related to computer use and realised that with the typical keyboard with numeric pad and a mouse setup, that my body was twisting more due to the mouse being more to the right than it needed to be. Using my left hand instead means less twisting as there's no numeric keypad on the left.

It took probably a couple of weeks to get comfortable with left-handed mouse use and these days, I am fairly ambidextrous on a computer.

The other thing that makes me think that handedness can be learned is learning to juggle. I found that it's easier to start doing a new movement (i.e. a trick) with my right hand, but once I learn it with my left hand, the left hand becomes more accurate than my right.

[markb139]

I’m a leftie and I don’t think I learnt it. My mother said as a very young child she noticed I’d mainly used my left hand to take things - probably food :) These days the only real problem for me is scissors, especially the ones with moulded plastic handles.

[ndsipa_pomu]

I didn't mean that most people don't have an innate handedness, but that it's quite possible to learn to do tasks with your non-favoured hand - it just takes a period of adjustment during which it feels incredibly clumsy to use that hand.