October 18, 2019

The Evolution of Hearing

Mammals exhibit remarkable variety in their sense of hearing; from elephants communicating with infrasonic sounds to bats navigating their environment through echolocation calls at ultrasonic frequencies, many non-human mammals hear outside the typical human hearing range. Interestingly enough, this large variance in sound perception finds its basis in the smallest of mammalian bones – the ossicles of the middle ear.

The mammalian middle ear is composed of three bones: the malleus, incus, and stapes. Though their function of transmitting sound waves to the inner ear for eventual processing by the brain is understood, the evolutionary history behind these small bones (the smallest in the human body actually!) has been an area of active research in the fields of paleontology, biology, and anthropology. To better understand this evolutionary event, let’s turn to our fellow vertebrates, reptiles.

No species has 'better' hearing than another; they just need to hear in a way that increases fitness in their respective environments.

Unlike mammals, animals such as lizards and crocodiles have more bones in their jaw and only one ossicle in their inner ear. Multiple lines of evidence from evolutionary developmental biology and a remarkably complete fossil record indicate that not only is this bone homologous with the stapes, but that the remaining bones in the mammalian ear, the malleus and incus, are actually found in the reptile jaw. Over time, these bones were incorporated in the mammalian middle ear. Does this mean mammals have a superior sense of hearing compared to reptiles? Not necessarily–no species has “better” hearing than another; they just need to hear in a way that increases fitness in their respective environments.

The development of an activity kit for this piece of evolutionary history was an exciting opportunity, allowing me to function as an educator in contrast to my daily experiences as an undergraduate student. However, I found myself thinking of the pedagogical methods I often wish were present in my academic experience, such as appealing to multiple learning styles and making the institution of science feel like an approachable, inclusive space. Yes, the evolution of the middle ear is an interesting topic, but what’s the impact of science outreach if an activity makes scientific knowledge feel inaccessible to participants? As a young scientist, breaking down boundaries to make the field of science accessible was a guiding principle behind the creation of this kit, and will continue to guide me in my future endeavors as an educator.

Ear bones

The Evolution of Hearing activity is broken into three parts: participants explore how various animals interact with the world through sound, build 3D models of middle ears from multiple species to observe evolutionary processes, and reflect on the multiple ways humans are able to communicate with one another. My personal favorite portion of this kit is the reflection on human communication, achieved through a game in which verbal, non-verbal, and written communication are utilized in a partner activity.

My hope is that participants in the Evolution of Hearing activity not only realize that no species has superior hearing to another, but that this logic also applies to hearing and communication between humans. Regardless of how a human individual experiences the world in relation to sound, there are many ways to communicate that are wholly effective and valid. This kit aims to create an atmosphere in which dialogue related to inclusivity can be cultivated alongside the acquisition of evolutionary knowledge, holding space in a way a lecture-based activity would struggle achieving.

Of course, this activity will always be evolving, adjusted to feedback given and further consideration on how this activity is received with regard to learning styles, language, culture, accessibility, and more. Creating this kit during my internship has been an invaluable experience, and I’m grateful to have contributed to NCSE’s mission through this project.

Anna Ginther is a senior at UC Berkeley studying Integrative Biology and Anthropology. She plans on pursuing a graduate degree in the biological sciences with the intent of one day becoming a college professor. The Evolution of Hearing activity kit is still in production; its activity guide will be available soon. In the meantime, check out all of NCSE's activity kits.

NCSE intern Anna Ginther

Anna Ginther is a volunteer with NCSE.