The human ear contains a set of small, often overlooked muscles that represent a relic of our mammalian ancestry. These structures, known as the auricular muscles, are largely non-functional in modern people, classifying them as vestigial features. Their presence raises a question about their original purpose. They once performed a survival function that enhanced the ability of early mammals to process their acoustic environment.
Identifying the Auricular Muscles
The extrinsic auricular muscles are a group of three thin skeletal muscles connecting the outer ear, or pinna, to the surrounding scalp and skull. They are named the Auricularis anterior, Auricularis superior, and Auricularis posterior. They originate from the epicranial aponeurosis or the temporal bone and insert directly onto the cartilage of the ear.
All three muscles are innervated by the facial nerve. Although present in nearly all humans, their function is minimal, typically causing only a slight tension in the skin or movement of the scalp rather than actual ear rotation. While some individuals can voluntarily move their ears, this action provides no discernible hearing advantage.
The largest of the group, the Auricularis superior, is located directly above the pinna. The Auricularis posterior sits behind the ear, and the Auricularis anterior is positioned toward the front. In the few people who can achieve ear movement, the action is often a result of these three muscles working together to pull the ear upward, backward, and forward, respectively.
The Original Role of Ear Movement in Mammals
For many other mammals, the auricular muscles are highly developed and perform sound localization. This is achieved through rapid, precise rotation of the pinna, which acts like a directional acoustic antenna. Animals such as deer, cats, and horses use this mobility to scan their surroundings for the source of a sound without having to move their entire head.
This ability to quickly and independently move the external ear is vital for survival, allowing an animal to instantly triangulate a sound’s origin for predator detection or hunting. By changing the angle of the pinna, the animal alters the way sound waves reflect into the ear canal, generating spectral cues. These cues help the brain determine whether a sound is coming from above or below, and from the front or the back, overcoming front-back confusion.
A mobile pinna also enhances the two primary methods of horizontal sound localization: interaural time difference and interaural level difference. By rotating the ear toward a sound source, the animal maximizes the intensity of the sound entering that ear, improving the signal-to-noise ratio. This mechanism is especially helpful in complex or noisy auditory environments where a single sound must be isolated from background noise.
The coordinated movement of the pinna is reflexively coupled with the animal’s overall orientation response, often preceding eye and head movements in response to an auditory target. The speed of this reflex allows the animal to gain a fraction of a second advantage in orienting its senses toward a potential threat or meal.
Why Humans Lost the Ability to Wiggle Their Ears
The loss of functional auricular muscle movement in humans is an example of an evolutionary trade-off, where an ancestral trait became redundant. As hominids evolved, the selective pressure to maintain mobile ears decreased around 25 million years ago. This shift occurred because humans developed alternative, more efficient methods for sound localization.
Increased mobility in the neck allowed early humans to quickly turn their entire head to face a sound source. This head rotation rapidly shifts the ears, providing the brain with the necessary binaural cues—the time and intensity differences between the two ears—to pinpoint the sound’s location. This mechanism rendered the small, independent movements of the pinna less necessary.
While the auricular muscles are still physically present, their motor control pathway has diminished in neurological prioritization. The brain’s auditory centers began to rely more heavily on processing complex signals from fixed ears combined with head movements.
Recent studies show these muscles subtly activate when people are straining to hear in difficult listening situations. This activity suggests a subconscious attempt to orient the ear toward the sound. However, the resulting ear movement is so minuscule that it provides no perceivable benefit to hearing.