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.