Why do we have a dominant hand?
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Hand preference probably arises as part of the developmental process that differentiates the right and left sides of the body (called right-left asymmetry). More specifically, handedness appears to be related to differences between the right and left halves (hemispheres ) of the brain.
When it comes to importance, dominance is needed for different tasks throughout the day, whether it is our writing, holding an object, cutting, and also brushing teeth. Having a consistent hand preference or an established hand dominance is important as it allows us to do tasks more efficiently and skillfully.
Your brain has two halves. Broadly speaking, each half controls a half of your body. So if you want to be equally good at writing with both hands, you have to spend the time and resources learning how to write *twice*. What a waste! Save some of the time and resources by just learning it once.
But, it’s not like your non dominant hand is useless. While your dominant hand is learning the fine control needed for writing, your left hand is learning to hold the paper steady. Sure, it’s not as difficult, but my dominant hand personally feels really awkward when I try to switch.
No other creature, not even the closest primates have a dominant hand. It is something unique to humans and earlier Homo species like the Neanderthals and even earlier ancestors, and just like today they were mostly right-handed. The evidence for this is in things like cave paintings (hunters were shown holding weapons in the right hand) and skeletons (the right arm bones were larger which is the case in modern humans to). One theory is the part of the brain to do with tool use is known to reside in the left-side of the brain so when we started to use tools heavily we evolved to become right handed (the left side of the brain controls the right side of our body). What’s interesting is that we aren’t 100% right-handed as a species, there is some kind of evolutionary benefit for some of us to be left-handed. Some of that could be to do with the brain and how the two hemispheres are linked differently in left handed people, another hypothesis that left-handed people appear to have a slight benefit in physical combat (it may also explain why left-handedness is more common in men than women). If all you are used to fighting is right-handed people and you suddenly encounter someone left-handed you are at a disadvantage. It is still a thing in modern sports like boxing, lefties win more.
It turns out the vast majority of things we do with our hands is boring, but a subset of what we do requires real dexterity. As we became tool makers, the percentage of things that required dexterity has increased.
Putting extra brain capacity into a single hand, rather than spreading it across two hands allows that single hand to be even better than it otherwise could be. It makes possible many things that two balanced, but less capable hands could never do.
I don’t think we have a dominant hand. We have a comfortable hand. Kids choose a hand and use it for their first 10 years of life and that’s the best hand. That muscle memory is set. It seems logical that you could force any child to use a left or a right hand and it would end up being dominant. I have no answer to why it’s like a 90/10 split organically. Why do all highschool kids draw weird S symbols. I’m drunk, I’ll see myself out.
And what about dominant eye? I’m right handed buy I’m sure my left eye is dominant.
Well, I guess being right-handed does have its advantages… unless you’re a lefty in a boxing ring!
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