Definitions of pain across disciplines associate pain with discomfort. Physiology links pain to discomfort to make humans aware of imbalances in the body. Biology links pain and discomfort as an evolutionary tool. Humans avoid discomfort/pain and this makes them survive. Psychology associates pain with discomforts of the mind. Pain is described by all disciples as a subjective experience, which can only be explained by those who experience it. Pain is related to illness of the "body", from the physiologist's point of view, or of the "mind" from the psychologist's point of view.