Maslow's hierarchy of needs
In simple creatures such as rodents, physiological needs may be the only needs that have to be met. However, in humans, this is only the base of the hierarchy. After physiological needs are met, there are four higher levels in the hierarchy. People are often not aware when their physiological needs are being met. However, when these needs are not met it becomes very obvious. For example, most humans do not think about each inhale and exhale they take. This satisfies their need to breathe. However, if the oxygen supply were cut off, all people would immediately become aware of the need to breathe. Physiological needs are important from the time a person is born and throughout their entire life.