system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: When does our brain choose our dominant hand?
gpt
It’s not entirely clear exactly what causes someone to be left or right handed, but it’s probably genetic. So it’s not really your brain choosing, it’s just how the chips fall when you’re conceived. 

The current theory is that basically the left side of your brain handles language and also controls the right arm. So as we developed written language, it became beneficial to basically have the hand you write with be controlled by the part of the brain deciding what to write. So a gene that made people right hand dominant became favorable. 

There isn’t actually a similar left handed gene. You either have the right handed gene, or a different gene that could wind up going either way. You could have this second gene and still be right handed.