There are many the orie so faging,but virtually all fall in to the category of hypotheses with aminimum of supporting evidence.One view point is that aging occursas the body's organ systems become less efficient.Thus Failures in the immune system hormonal system,and nervous system could produce characteristics that we associate with aging. Following A Different Vein,many current researchers are looking for evidence at the cellular and subcellular level. It Has Been Shown That Cells Such As Human Fibroblasts(generalized tissue cells) grown in culture divide only limited number of times and then die. Only cancer cells seem immoral talin this respect.Fibroblast cells from an embryo divide more times than those taken from an adult.Thus some researchers believe that aging occurs at the cellular level dispartof the cell's genetic makeup.Any event that disturbs the cell's genetic machinery such as mutation, damaging chemicals the cell's environment,or loss of genetic material, could cause cells to lose their ability to divide and thus bring on aging. Other Theories Of Aging Look At Different Processes.
Chronological aging refers to the passage of time ince bir that is usually measured in years. While chronologic algae can be useful in estimating the average status of large group of people.it is apoorin dicatoro fans individual person's status because there is a tremendous amount of variation from one individual to the next in regard to therateat which biological age changes occur. For Example,ontheaverage, aging results in people losing much of their ability to perform strenuous activities,yet some elderly individuals are excellent marathon runners..
Another type of aging is cosmetic aging, which consists of changes in outward appearance with advancing age.This includes changes in the body and changes in other aspects of a person's appearance, such as the style of hair and clothing,the type of eyeglasses,and the use of a hearing aid. Like Chronological Aging, it is frequently used to estimate the degree to which other type so aging have occurred.However,it is an inaccurate indicator for other purpose because of variation among individuals and because of variation among individuals and because a person's appearance is affected by many factors that are not part of aging including illness,poor nutrition, and exposure to sunlight.