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).
Theories of Aging. Philosophers and scientists have long been studying experimental evidence and using observations of the natural world to try to develop a theory or theories explaining why and how we age. As late as 1990, researcher Zhores Medvedev tried to categorize more than 300 theories of aging. More recently, scientists have started to come to a consensus about why we age. They have also narrowed the specifics of what affects how we age down to several significant, and likely complementary, hypotheses.