Not to toot my own horn or anything, but I can extend my empathy beyond myself just enough to imagine someone else’s perspective, fully knowing I’ll never completely understand the texture of their experience. But as a right-handed person, I will never, ever be able to do that for left-handed people. There’s just something in my brain preventing me from understanding how someone can navigate the world primarily using the hand I mostly rely on to accidentally test the sharpness of kitchen knives.

So naturally, it always made sense to me that around 90 percent of humans are right-handed. What never made sense was why. According to new research published in PLOS Biology, we may have finally figured it out: humans became overwhelmingly right-handed because we started walking upright and developed massive brains.

Researchers from the University of Oxford analyzed more than 2,000 primates across 41 species, comparing handedness with factors like social behavior, diet, body size, and movement. Nothing fully explained humanity’s innate steadfast dedication to right-handedness until researchers started factoring in brain size and the ratio between leg and arm length.