Hearing may initially have been important to vertebrate as a mechanism to alert them to dangerous activities. It also important in search for food and mates and in communication. Humans are not able to hear low pitched sounds, below 20 cycles per second. Here also focus on Structure of human Ear: The human ear has three divisions: the outer Ear; the middle Ear (eardrum) and the inner Ear. The process of hearing can be summarized as follows; Sound waves enter the outer ear and create pressure waves that reached the tympanic membrane. Air molecules under pressure vibrate the tympanic membrane.