How Hearing Evolved | Evolution Of The Brain - Episode 4

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How did the brain evolve? Why do we have a brain? What functions did our brains aqcuire over millions of years of evolution? Find out all about it in this new mini-series documentary: Evolution of the Brain.

In this fourth episode of the brain evolution documentary, we look at the evolution of hearing. We will discuss how hair cells evolved, which are the cells in the ear that pick up sound. We will see how these hair cells work and how they are able to detect sound from different direction and of different frequencies. Particularly mammals have a great sense of hearing. As soon as we see the first mammals, around 200 to 150 million years ago, we see multiple changes to the inner, middle and outer ear. As such, humans actually have quite good hearing, compared to other mammels. Altough, of course, our hearing is not as great as that of dogs, cats, rats, dolphins, bats and many other mammals.

Initially, hair cells evolved in our underwater living ancestors some 430 million years ago. Some developed to detect sounds, whereas others detect imbalances. In early evolution various brain structures evolved, such as the superior olive and inferior colliculus. Both regions are crucial for detecting different frequencies and are able to figure out if a sound comes from left, right, above or below. Later in our evolutionary history, the middle and inner each changed. Rather than a single bone, three bones connected the ear drum and inner ear. This led to the development of new brain structures, including the medial geniculate nucleus and auditory cortex. In addition we see secondary auditory regions in the neocortex, which enable us to make vocalization. A skill that humans perfected by the development of language.

Production, narration, and story: Miles Wischnewski, PhD. 2021.

Time stamps:
0:00 Introduction
0:20 Smell is not enough to sense invisible dangers
1:00 Why hearing evolved
2:59 Evolution of hair cells
4:34 How the first hair cells worked
7:08 Superior olive and Inferior colliculus
9:44 Evolution of the middle ear in land animals
11:10 Changes to the inner ear in land animals
12:19 Medial geniculate nucleus
13:06 Middle and outer ear development of mammals
14:28 Auditory cortex
16:08 Understanding vocalizations and language
17:30 A rich experience of the world around us

References/resources:

Otolith MRI scan:(Youtube channel: Sarah F).
CNS mouse brain (Youtube channel: mesoSPIM).

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