system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is the right hand more likely to be the dominant one?
gpt
Short answer: we don't really know.

There is definitely a social component: for a long time lefties were trained to use their right hand instead. But this was because people were overwhelmingly right-handed to begin with. So it doesn't explain why righties are more common; it just means they are a little less common than we thought. Past rates of lefties is around 6-8% in times when right-handedness was enforced, compared with 10-12% lefties today.

There are advantages to having a dominant hand in nature: it means you can specialize your tool use and manipulation to one stronger, better-controlled hand. Many animals favor one limb over the other. It's not hard to imagine the benefits. But that doesn't explain why it should usually be the right hand. For example, chimps favor one hand, but it's somewhere around 50/50 to 67/33 in favor of righties. So this doesn't explain why we tend to favor the right.

This leads us to the theory that we have a gene that controls hand dominance, but instead of the options being right and left, the options are right-handed and random, meaning that these people could wind up with either hand dominant. This would go a long way to explaining why righties outnumber lefties 9 to 1.  This is called the dextral/chance model.

But current research shows that it's far more complex than that. The genetics of handedness do not come from a single gene, but some interaction between a number of genes, perhaps hundreds.  We also now know that handedness is not strictly genetic: identical twins for example aren't any more likely to have the same dominant hand than fraternal twins.

But none of this explains why the right hand is the popular one. For a long time, scientists have suspected it had to do with the development of language, because the right hand and language processing are both controlled by the left side of the brain.  So maybe when we were developing language, it caused us to tend to be righties.  Left-handed people also tend to process language on the left side of the brain, so the solution isn't as simple as mirror brain layouts. Best guess is that language processing improved the left side of the brain, which made it advantageous to favor the right hand.