The areas of the tongue sensitive to tastes. The classical theory about the physiology of taste recognizes the existence of four fundamental tastes - sweet, salty, sour and bitter - each being perceived by specific areas of the tongue by means of gustatory receptors, also known as taste buds.
Theories of Aging. Theories of Aging. Erik Erikson, who took a special interest in this final stage of life, concluded that the primary psychosocial task of late adulthood (65 and beyond) is to maintain ego integrity (holding on to one's sense of wholeness), while avoiding despair (fearing there is too little time to begin a new life course).
As summarized below, aging theories propose three different answers to this question and are based on three different versions of Darwin's survival of the fittest idea. Simple Deterioration Theories - Fundamental Limitations - Wear and Tear. Many people believe that biological aging is simply the result of universal deteriorative processes such as oxidation, entropy, or wear and tear that cause aging in machinery, exterior paint, and other inanimate objects.