Previously Undiscovered Protein Gives Us an Advantage in Hearing
We humans—like mammals in general—owe our evolutionary success in part to our excellent hearing. Biologist Isabelle Lang has now discovered the reason for this.
At a Glance
- Human hearing—like that of all mammals—is more sensitive, more capable, and covers a wider frequency range than that of other species.
- The reason for the efficiency of our hearing is the complex structure of the cochlea.
- Until now, it was assumed that potassium and calcium were necessary for the highly complex hearing process in the inner ear.
- However, biologist Isabel Lang has discovered through studies of mice that a protein called LRRC52 is a component of the sensory hair cells and enables them to function independently of calcium influx.
Those who don’t want everyone to eavesdrop communicate in frequency ranges that only certain individuals can hear. The police still use this principle in their radio communications today, as do many intelligence agencies and their criminal adversaries—and it is one reason for the evolutionary success of mammals. During the age of the dinosaurs, mammals were able to evolve undisturbed because they communicated with one another on frequencies that their predators—including the dinosaurs—could not hear.
We Hear More Than Other Species
This vital protection was only possible because mammals can hear across a wider frequency range than other classes of animals. Birds, for example, can only perceive sounds up to a frequency of three kilohertz (kHz). Our human hearing covers the wide frequency range from 20 hertz (Hz) to 20 kHz. Many smaller mammals can even hear into the ultrasonic range, allowing them to receive signals that are inaudible even to us humans. Absolute specialists in this field are bats, which can hear sounds up to 200 kHz and use their hearing as a radar to locate objects. Dolphins are the leaders among high-frequency listeners: they perceive sounds in the ultrasonic range of over 100 kHz.
Recommendation: Get a hearing test every two years starting at age 45
- The frequency range we can hear when we’re young extends from about 20 Hz to 20 kHz.
- As we age, however, our ability to hear high-pitched sounds gradually declines.
- That’s why it’s especially important as you get older to have your hearing tested regularly so that any hearing loss can be detected early and addressed.
- Hearing care professionals recommend having a hearing test every two years starting at age 45.
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Our highly developed sense of hearing thus plays an important role in the success of our species in general. This is because, for humans and mammals, hearing serves not only for communication but also for spatial orientation and for detecting danger. Marine mammals such as whales and dolphins, for example, navigate the dark depths of the oceans using only their sense of hearing. To estimate water depth and distances and to locate their prey, whales use what is known as echolocation: They generate sound waves that—when they strike an object—bounce back to them, providing an accurate picture of their surroundings in a matter of seconds. Using these short clicks or long, deep tones, these giants of the sea also communicate with one another on their own unique frequencies.
Coils in the ear help us hear better
However, the process of sound processing in the inner ear is so complex that it has not yet been fully researched down to every last detail. Why human hearing is more powerful than that of other species, on the other hand, is well understood: The efficiency of our ears stems from the structure of our cochlea. In mammals, the cochlea is coiled, relatively long, and—much like a guitar string—mechanically tuned. Birds, on the other hand, have only a comparatively simple, electrically tuned counterpart in their inner ear that cannot process high-frequency sounds.
When a sound wave strikes this cochlea, it triggers a highly complex physiological reaction that converts the vibrations of the air into acoustic signals and sends them to our brain: The incoming sound wave stimulates the sensory cells of the ear, known as hair cells. These signals are transmitted to the brain by nerve cells. There, the auditory cortex—the brain’s hearing center—decodes the stimuli, recognizes various sounds and music, and understands when someone is speaking to us.
How does our sense of hearing work?
- Sound waves stimulate the outer ear, which transmits these vibrations to the eardrum.
- The eardrum begins to vibrate, transmitting these vibrations to the ossicles.
- At the junction between the eardrum and the malleus, incus, and stapes, the sound pressure is amplified by a factor of 20.
- The movable foot of the stapes transmits the sound pressure to the cochlea.
- Inside the cochlea, a membrane is set into vibration.
- Hair cells in the fluid surrounding the cochlea convert these waves into electrical impulses, which the auditory nerve transmits to the auditory cortex in the brain.
Protein Discovered as the Key to the Mystery of Our Hearing
The minerals potassium and calcium play a crucial role here; they ensure that this chain reaction takes place and subsequently return the hair cells to their original state so that they can once again detect new sound waves. Until now, researchers had assumed that both substances were necessary for signal transmission in the inner ear—as is the case, for example, in birds. Scientific studies show that the auditory nerve does not send impulses to the brain when calcium is not present. In mammals, however, this signal transmission is activated regardless of whether the hair cells transport calcium or not. The mechanism underlying this phenomenon has long puzzled scientists. Biologist Isabelle Lang of Saarland University has now answered this fundamental question: She succeeded in demonstrating that a protein called LRRC52 is responsible for the fact that the hearing of mammals functions differently from that of birds.
A Chance Discovery Solves the Mystery of Our Hearing
The scientist discovered this auditory advantage of our species by examining the hair cells of mice before and after the twelfth day following their birth. From this point on, the rodents are able to hear. In the hair cells of mice that were not yet able to hear, the protein LRRC52—which is responsible for hearing—was not detectable. In the older mice, however, it was found precisely where the channels that transport calcium were located. This allowed Lang to demonstrate that the protein is a component of the auditory sensory cells that enables them to function independently of calcium influx. In this scientific breakthrough, however, chance also played into the researcher’s hands: Other research groups around the world, who were trying to solve the mystery of the efficiency of human hearing, had not suspected that the protein played any role in hearing at all. In fact, it is the reason why our hearing is more sensitive and capable—because it recovers more quickly than the ears of other species and covers a wider frequency range.
Our highly capable, efficient sense of hearing has not only given us many advantages throughout the course of evolution, but also provides us with vital services every day. Here you'll find useful information on how to protect your ears.
