Eli5:what’s the cause of someone being right or left handed? And why the vast majority is right handed?
In: Biology
The majority of humans are right handed because of how the brain develops.
The left hemisphere control the right side of the body and the left hemisphere usually develops faster/first.
I’m a lefty, my hubby is a lefty. You’d think we’d only have left handed kids. Nope, one of each. Really messed with the right handed kid to transition from our left handed house to a right handed world.
I was born right handed and when growing was doing everything with my right hand.
When I was like 3 or 4 I broke a couple fingers on my right had and had to wear a cast that restricted my whole hand. I started doing stuff with my left hand and when the cast came off I never went back to using my right hand. Even to this day, almost 40 years later, I can’t hold a pencil or throw accurately with my right hand.
It makes me think it is a co boating of mental is physical development.
Short answer: We don’t really know.
Longer answer: A lot of smart people have been trying to answer this question for many years. And there’s a lot of ideas and theories, and a lot of supporting evidence for many of those theories (how speech processing tends to be on the same hemisphere of the brain that controls the dominant hand, how having a small percentage of the population being left-handed could lead to evolutionary survival advantages especially in regards to fighting against right-handed people, genetics, etc.). However, nothing has really come out as THE conclusive reason why 90% of people are right-handed and only about 10% are left handed.
This video does a good job of explaining this phenomenon, and what we know and still do not know: https://youtu.be/NPvMUpcxPSA?si=8BzpefrQMfCdsif4
I’m ambidextrous. I can write with both but prefer my left to write. I do most everything else with my right (throwing a ball, bowling, etc.). I use the computer mouse with my left. I never knew that people put their makeup on with just one hand until I started watching videos. I use my left hand for the left side of my face and my right hand for the right. I never knew I was different with any of it until people started pointing it out to me. I remember my mom got called into my school when I was in 3rd grade. The teacher told her I must be bullying people into doing some of my work because it was in two different styles of handwriting. My mom had to explain that I was ambidextrous. I had to actually prove it in front of the teacher. She then told me I had to pick a hand to write with so I picked my left. I can’t write as fluidly with my right as I used to but I still can. For reference, I’m 60.
Father here. My family is right-handed, but I wanted my daughter to be left-handed. So since she was a baby, I urged her to lefthandedness. And she is left-handed now. I wanted her to be different in a better way.
I think righthandedness goes back throughout history, and I don’t know why.
I had a an Eastern European grandmother who smacked me everyone I used my left hand without my parents knowing. It really messed me up.
It was once believed that the left hand was “sinister” or “wicked.” That’s probably the best explanation so far.
Lots of ideas, not a lot proven yet. The lobes of the brain and their control over different aspects seem to be most likely. We see effects from this in many ways.
One interesting reason proposed is that we tend to carry babies on our left side. Which leaves our eventually dominant hand free for tasks. There are various things associated with holding babies on the left such as the baby hearing a heartbeat, or it being a less sensitive breast, or even that communicating and connecting is better that way because of brain arrangement. But it’s also possible that we carry babies on our left because we tend to be righthanded since people tend to carry babies in their less dominant arm.
Fun fact, you have a dominant leg (makes the first step, differences in balancing and pushing off), dominant eye (preferred for looking through microscope), even a dominant ear (one ear is usually the one that gets an earbud left in when trying to hear what someone says to you). These can be the same as your handedness but can also vary. Most righthanded people tend to overall have a right-side dominant, but lefthanded people usually vary more. Here’s a fun little way to test [https://www.scientificamerican.com/article/bring-science-home-dominant-side/](https://www.scientificamerican.com/article/bring-science-home-dominant-side/)
Personally, I’m a bit skeptical that we tend to be righthanded because we carry babies with our left. Because animals usually also have dominant sides. They seem to tend to be more evenly split than humans though. Although female cats tend to be more often right-pawed.
I’m a lefty (from a family of five where every single person was lefty); my wife and her mom are righty, but supposedly my FIL was born lefty but the nuns beat it out of him in parochial school…who knows.
Anyway.
We have fraternal twin boys.
Twin #1:
– 100% righty for writing
– 100% lefty for kicking
– 50/50 for throwing
Twin #2
– 100% lefty for writing
– 100% righty for kicking
– 50/50 for throwing
Odd twist:
– they both have simian creases on both left and right hands (and so do I). I only recently discovered this phenomenon. Apparently it’s only in 1.5% of the population…FOR ONE HAND.
Me, and my twin sons all have it both hands. I’d love to know the probability for that.
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