The ability to perceive sound is critical for the survival of most species on Earth, including humans. The ability to assess the environment through hearing evolved in a variety of ways in the animal kingdom, and high-functioning animals such as humans adapted the sense of sound as a means to communicate.
Sound is created when mechanical energy travels through an elastic medium, such as air. These waves of energy travel into the ear, where the brain interprets them as sound, alerting the listener to potential predators, environmental threats, food, water or peers. Hearing the sound of an approaching tiger, an impending waterfall or a potential meal increased the chances of early human survival. The development of language increased human reliance on hearing as humans learned to express more complex ideas through sound.
In modern times, hearing traffic or the din of a restaurant alerts people to the same dangers and attractions. Humans and animals began using vocal communication long before the development of language, alerting one another to threats, food and mates. The great apes, such as chimpanzees and gorillas, provide excellent examples of pre-language vocal communication. When observed in groups, they can be seen communicating with one another through a variety of sounds and gestures.