Are you a “southpaw?” If so, you’re in a minority; only about 10% of the human population is left handed.
(Much smaller minorities are ambidextrous, capable of using both hands equally well, and mixed-handed, meaning you find some tasks easier with the left hand and others with the right).
All mammals show side preferences. We have a good model for this in an animal that we use for tasks and who’s side preference matters: The horse.
Are Horses Right-Hooved?
In horses, side preference manifests as a greater willingness and ease to turn in one direction over the other. The majority of horses have a “weak side,” which has to be strengthened with training and exercise (something they aren’t always happy about).
Side preference is stronger in some animals than others.
However, there’s a clear difference between horses and humans…and this difference is the same for other mammals.
Horses split about 50/50 as to which side they prefer. There is a slight preference for turning left, but this may reflect animals with a very low side preference and the fact that in most traditions, animals are always worked from the left side (Spain is a peculiar exception here).
So, why are most humans right handed? There are a bunch of theories on this.
Why are Most of Us Right-Handed?
We’ve hunted for a biological reason for the right hand bias for years. A recent study identified…41 gene variants linked to being left-handed. Except that those things only explain about 12 percent of the variation in handedness. Oops?
So, let’s drill down on this. We assume being right- or left-handed is genetic, but what if it isn’t? One controversial study suggests that what is genetic is how strongly we prefer one hand over the other.
But the studies point towards something intriguing:
Our handedness preference is not genetic at all.
Only a small number of individuals have such a strong innate preference for using the left hand that it overcomes environmental influences.
Which leads us to…
Why are There Now More Left-Handed People?
That 10% number cited above? That’s how many left-handed people there are now.
You’ve probably heard 4% somewhere. It’s not wrong. That was the number of left-handed people in 1920.
So, huh. What, exactly, is happening here?
My mother was one of those people who is strongly innately left-handed. She basically had to use her left hand for anything requiring a lot of dexterity, like writing.
My mother was physically abused for being left-handed. Any time she tried to write with her left hand in elementary school, she was struck. The only result of this was a delay in her ability to write.
This was common when she was growing up. Being left-handed was considered to mean you were more prone to mental disabilities and retraining kids to be right-handed was the “cure.”
And it hasn’t entirely gone away. My husband is also strongly left-handed. No, that’s not why I married him. He almost failed kindergarten because they only had right-handed scissors. (Why would they even have…never mind).
So, the increase in people being left-handed may well be a result of, drumroll, not punishing people for being left-handed.
When there’s a bias against “lefties,” only people with a strong wiring that way will be left-handed. Take away the bias and people with a slight leaning, given the choice, will be allowed to be left-handed. Ambidextrous kids may choose to be left-handed if their parents are.
So, Why Did We Hate Lefties?
That bias against left-handed people can’t have emerged in a vacuum.
So, here’s something to consider:
It’s easier to build technology if people are one way or the other. We’ve already mentioned handed scissors, but the key difference between us and other mammals is extensive tool use.
A right-handed fencer who has never faced a left-handed fencer is at a substantial disadvantage. Castles were built with the assumption that everyone was right-handed.
At some point in our past a tiny preference for the use of the right hand caused us to build tools with the assumption people would use the right hand.
This then would lead to a bias in favor of the right hand. People with only a weak preference would use the right hand. Lefties would be selected against.
It doesn’t matter to a rider which side of a horse is weak except that you watch for it and make sure to work them a little more on that side. So there’s no selection pressure for or against “right-hooved” horses.
In humans, though, we’ve forced ourselves to be right-handed.
Now that we’re not doing that as much, though, will we slowly drift back to 50/50 like other animals? Will typing, which uses both hands, cause kids to develop less handedness?
But it certainly seems that human handedness is as much environmental as genetic.