A subtle movement of the ears can sometimes be observed when individuals smile. This involuntary action highlights an intriguing aspect of human anatomy and its evolutionary journey. The underlying mechanisms involve specific muscle groups and neural connections, remnants of a more functionally significant past.
The Muscles Involved
The movement of the ears is attributed to a group of three muscles located around the outer ear, known as the auricular muscles. These include the anterior auricular muscle, the superior auricular muscle, and the posterior auricular muscle. The anterior auricular muscle pulls the ear forward, the superior auricular muscle lifts it, and the posterior auricular muscle draws it backward. These muscles are considered vestigial in humans, meaning they have largely lost their original function over evolutionary time.
All three auricular muscles receive their motor commands from branches of the facial nerve (cranial nerve VII), such as the temporal branch and the posterior auricular nerve. In most individuals, these muscles are underdeveloped and not under conscious control. However, their connection to the broader facial musculature means they can sometimes be inadvertently activated during strong facial expressions, such as a wide smile, resulting in the observed ear movement.
An Evolutionary Perspective
The presence of auricular muscles in humans, despite their limited function, offers a glimpse into our evolutionary history. In many other mammals, such as cats, dogs, and monkeys, these muscles are highly developed and functional, allowing them to swivel their ears independently. This ability is crucial for sound localization, helping animals pinpoint the source of sounds to detect prey or predators. Our distant ancestors likely possessed a similar capability, relying on ear movement to enhance their auditory perception.
Over millions of years, as humans evolved to rely more on visual and vocal communication, the evolutionary pressure to move the ears diminished. Consequently, the auricular muscles became smaller and less functional, becoming a vestigial trait. Although largely non-functional for conscious ear movement, the neural circuits for ear orienting have persisted in a rudimentary state for over 25 million years. The subtle ear movement seen in some individuals is a biological remnant of our ancestral past.
Why Some Can and Others Can’t
The ability to move one’s ears, particularly in conjunction with facial expressions like smiling, varies significantly among individuals. While everyone possesses the auricular muscles, the degree of their development and the precise neural connections between these muscles and the facial nerve differ from person to person. This variability suggests a combination of genetic predisposition and individual neurological wiring. Some research indicates that the ability to wiggle ears may not follow a simple dominant inheritance pattern, as cases exist where individuals can move their ears even when their parents cannot.
The neural pathways governing these vestigial muscles are not typically under conscious control for most people. Even when ear movement occurs with a smile, it is often an unconscious, involuntary action tied to the broader activation of facial muscles. While some individuals can learn to voluntarily control these muscles through practice, for many, the movement remains a subtle and unintended consequence of their facial expressions. This phenomenon is an individual variation, highlighting the diverse ways human anatomy expresses its evolutionary heritage.