Tens of millions of years ago, our ancestors could swivel their ears to pick up sounds, much like cats and dogs do today. Humans lost that ability over time, and the muscles that once controlled ear movement are now mostly useless—except for a few people who can still wiggle their ears. But new research shows that these muscles still react when we listen intently, hinting at their primordial function.
Researchers in Germany and the U.S. found that the muscles once used to move our ears, known as auricular muscles, still activate when we focus on competing sounds, as if trying to revive our distant ancestors’ ability to swivel or prick our ears. Though it’s unclear if this improves our hearing abilities today, their research indicates that the harder we try to listen, the more we engage those muscles. Excitingly, the findings also shed light on a vestigial part of our body—and a once-useful ability lost to evolution.
“There are three large muscles which connect the auricle to the skull and scalp and are important for ear wiggling,” Andreas Schröer of Saarland University, who led the study, said in a statement by the journal Frontiers. “These muscles, particularly the superior auricular muscle, exhibit increased activity during effortful listening tasks. This suggests that these muscles are engaged not merely as a reflex but potentially as part of an attentional effort mechanism, especially in challenging auditory environments.”
Previous research had already linked activity in the posterior and superior auricular muscles (the largest auricular muscles) to attentive listening, suggesting that our primate ancestors used them to move their ear shells and funnel sounds to their eardrums. Schröer and his colleagues, however, wanted to determine whether the muscles were more active when people had to listen harder.
As detailed in a study published today in Frontiers, the researchers attached electrodes—devices that detect electrical impulses—to the auricular muscles of 20 participants without hearing problems, and instructed them to listen to an audiobook emitted from speakers. The participants listened to the audiobook at various difficulty levels, and took a quiz on its content at the end. Sometimes the researchers played a distracting podcast at the same time, and occasionally the sounds came from different directions—but the task was always achievable, according to the researchers. If the participant gave up because it was too difficult, the activity linked to auricular muscle effort would cease.
Ultimately, the researchers observed that the posterior and superior auricular muscles displayed different activity depending on the acoustic situation. The more effort participants exerted to hear the audiobook, the more the superior auricular muscles contracted. Additionally, when the audiobook played behind the participant, the participants’ posterior auricular muscles activated in a way that might have pointed their ears in that direction, if we still had that ability.
“The exact reason these [muscles] became vestigial is difficult to tell, as our ancestors lost this ability about 25 million years ago,” Schröer explained. “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.”
Ultimately, it seems like the superior auricular muscles reacted to how difficult the listening task was—activating more during the hardest listening tasks—whereas the posterior auricular muscles were triggered by the direction of the sound.
“The ear movements that could be generated by the signals we have recorded are so minuscule that there is probably no perceivable benefit,” Schröer added. “However, the auricle itself [the ear shell] does contribute to our ability to localize sounds. So, our auriculomotor system probably tries its best after being vestigial for 25 million years, but does not achieve much.”
What are the practical applications of these almost-useless ear muscles? Though the researchers admit that further research in more realistic conditions must confirm their results, superior auricular muscle activity could potentially serve as a physical indicator of listening effort.
So the next time someone demands, are you listening? watch out—they might soon have the tools to verify your answer.
