In order to present it as a mental illness there would have to be some kind of negative effect, wouldn't there? These differences you mention don't stand out as harmful or even disadvantageous.

You were probably a left-handed person who was taught to write/use tools with their right hand in kindergarten. I got this treatment too.

I'm sorta here too. I'm right handed, no external pressure to use one hand or the other in early age. Mother is a lefty, father is a righty. As a result I often used the computer mouse on either side as a kid, really wherever it was left by the last user.

Learned to shoot a bow as a kid but only learned as an adult I'm left eye dominant, and to take advantage would require re-learning the bow in my left hand(many many strikes on my arm sent be back to a righty). Shooting guns is a similar situation, but I'm a fairly good shot regardless. It definitely makes using sights weird.

I'm semi-ambidextrous too, with enough focus I can somewhat cleanly write with either hand, and I'm generally good with my hands in fine tasks, with only a minor preference to pick up a tool with my right hand.

I wonder how common this is. People seem surprised when I demonstrate my left handed writing.

> I've been told that it's effectively a mental illness if discovered during childhood (as is ambidexterity). Yet I can't help but think that it is not a mental illness, but rather something else.

https://en.wikipedia.org/wiki/Handedness#Types: “Mixed-handedness or cross-dominance is the change of hand preference between different tasks. This is about as widespread as left-handedness.”

⇒ about 20% of the population is not strictly right-handed. That’s not a majority, but I think the word to use for that is “normal”.

Left-footed and right-handed. I find my "handedness" follows where the activity is driven from (upper/lower body).

Soccer, snowboarding, batting, golfing: lefty

Writing, throwing, tennis, pool: righty