The mostly-useless muscles that try to move your ears
Whales have pelvises from their ancestors’ legs. Blind cave fish grow (before losing) eyes they never use to see. And humans, well humans grow quite a few body parts that we inherited from our ancestors, but haven’t quite gotten around to removing from our DNA. Tail bones, wisdom teeth and goosebumps on your skin all served more purpose in the past, but occasionally some new use can be attached these vestigial structures. A recent look at our ear muscles helped pin down their origins, but also found a use for them that may be a happy byproduct more than an evolutionarily-selected benefit.
Many mammals can still move their ears around at will. Cats, foxes, mice and more can adjust the angle of their ears to maximize their effectiveness, which is a trait that probably helped nocturnal animals navigate their world as far back as 150 million years ago. When more mammals became diurnal, that is, more active in the light of the sun, they became more reliant on vision, and thus adjustable ears weren’t as crucial. But that doesn’t mean we gave them up entirely.
Humans still have muscles and brain circuitry in place to move our ears. The catch is that the muscles are pretty weak, and our ears are pretty stiff, so not much movement is possible. While most of us never even think about trying to wiggle our ears, they may be trying to shift around anyway. Sensors found that when you hear a startling sound to your left or right that causes to to dart your eyes to the side, your ear muscles will also try their best to adjust also, even if there’s no real gains to be had in their orientation.
This close examination did reveal one potential utility for wiggling ears, which is that they may act as a very specific lie-detector. In the same way that a forced smile doesn’t use the same muscles as a real one, a real expression of joy will make your ears retract slightly. You can’t really fake that response, and so it may be a way to for psychologists to confirm when people are accurately expressing their happiness or not. It’s probably not enough to impress a cat or rabbit, but it’s more than we can say about your tail bone.
Source: Un-intelligent Design: No Purpose for Vestigial Ear-Wiggling Reflex by Stephanie Pappas, Live Science