system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Is the immergence of right or left brain dominance in a person truly random? Why is there such a disparity in the ratio between lefties and righties?
gpt
A lot of brain dominance stuff is overstated, and generally the stuff that we can say for sure about brain dominance is limited only to the speech processing centres (Broca's and Wernicke's area if you want to google it). These are found on the left side (left dominance) for most people, which would mean that it isn't random. 

Of note, is that left-handed people tend to more often have right-dominance for their speech processing centres, but we're not sure why. One running theory that ties handedness and brain dominance is that there's some gene that causes both left-handedness and right-dominance for speech processing. But there's no real proof of anything.

There's some stuff that shows that the right side of your brain is more activated during certain thoughts while your left side is more activated during others, but your brain dominance for speech processing doesn't necessarily mean that you're tilted towards being more emotional or more logical or whatever.