Throughout history man has had to accept the fact that all living things must die. And people now live no (1) than they (2) to. It is true that all living things still show the (3) of aging, which will eventually result (4) death. Aging is not a disease, but as a person passes maturity, the cells of the body and the (5) they form do not (6) as well as they did in childhood and adolescence. The body provides less (7) against disease and is more prone (8) accident. A number of related causes may (9) to aging. Some cells of the body have a fairly long life, but they are not (10) when they die. (11) a person ages, the number of brain cells and muscle cells decrease. Other body cells die and are (12) by new cells. In an aging person the (13) cells may not be as able to develop or as capable (14) growth as those of a young person. Another (15) in aging may be changes within the cells themselves. Some of the protein chemicals in cells are known to change with age and become less elastic. This is why the skin of old people wrinkles and (16) loose. This is also the reason old people (17) in height. There may be other more important chemical (18) in the cells. Some complex cell chemical, such as DNA and RNA, store and pass (19) information that the cells need. Aging may affect this (20) and change the information-carrying molecules so that they do not transmit the information as well.