Sound Muscles

Our evolutionary ancestors lost the ability to swivel their ears like dogs or cats millions of years ago.

However, vestigial ear muscles – remnants from our evolutionary past – still activate when focusing on a sound or when hearing becomes difficult, according to a new study in Frontiers in Neuroscience.

“There are three large muscles which connect the auricle to the skull and scalp and are important for ear wiggling,” lead author Andreas Schröer of Saarland University explained in a statement. “These muscles, particularly the superior auricular muscle, exhibit increased activity during effortful listening tasks.”

To test this, researchers wired up 20 participants with electrodes and played an audiobook while adding distracting background noise.

As the difficulty increased, participants’ superior auricular muscles – responsible for pulling the ear upward – activated more, as if trying to fine-tune hearing. When sounds came from behind, another set of muscles, the posterior auricular muscles, reacted as if attempting to rotate the ears backward.

The study builds on previous research showing that these muscles can still generate faint electrical signals, even if they no longer move human ears effectively.

“The exact reason these became vestigial is difficult to tell,” Schröer said. “One possible explanation could be that the evolutionary pressure to move the ears ceased because we became much more proficient with our visual and vocal systems.”

While the tiny ear twitches likely don’t improve hearing, this discovery could have practical applications. A future hearing aid that tracks ear muscle activity could detect when a person is struggling to hear and automatically adjust volume or settings.

“We have very, very good hearing aids now … and yet people still aren’t happy wearing them sometimes,” Alexander Francis, a professor at Purdue University who was not involved in the study, told NPR.

Matthew Winn, an audiology professor at the University of Minnesota, told NPR that the findings were compelling but suggested more research is needed to confirm whether the muscle activity directly reflects listening effort or is just frustration with background noise.