In a previous article, I looked at 93 measurements from the ANSUR-II dataset and found that ear protrusion is not correlated with any other measurement. In a followup article, I used principle component analysis to explore the correlation structure of the measurements, and found that once you have exhausted the information encoded in the most obvious measurements, the ear-related measurements are left standing alone.

I have a conjecture about why ears are weird: ear growth might depend on idiosyncratic details of the developmental environment — so they might be like fingerprints. Recently I discovered a hint that supports my conjecture.

This Veritasium video explains how we locate the source of a sound.

In general, we use small differences between what we hear in each ear — specifically, differences in amplitude, quality, time delay, and phase. That works well if the source of the sound is to the left or right, but not if it’s directly in front, above, or behind — anywhere on vertical plane through the centerline of your head — because in those cases, the paths from the source to the two ears are symmetric.

Fortunately we have another trick that helps in this case. The shape of the outer ear changes the quality of the sound, depending on the direction of the source. The resulting spectral cues makes it possible to locate sources even when they are on the central plane.

The video mentions that owls have asymmetric ears that make this trick particularly effective. Human ears are not as distinctly asymmetric as owl ears, but they are not identical.

And now, based on the Veritasium video, I suspect that might be a feature — the shape of the outer ear might be unpredictably variable because it’s advantageous for our ears to be asymmetric. Almost everything about the way our bodies grow is programmed to be as symmetric as possible, but ears might be programmed to be different.