The biology and t heories of aging.

Aging is a natural, time-dependent process characterized by irreversible changes in the molecules, cells, tissues, and organs. It occurs as a result of cumulative damage at different levels of the organization, in particular by damaging proteins and DNA. There is no single definition, nor a unique attitude about when and how age arises and what are its causes. The process is extremely complex and most likely a consequence of the effects of different mechanisms (not only genetic but also acquired) that lead to disrupt homeostasis, reduce stress resistance and the more frequent occurrence of the disease. There are many classifications of theories about aging and they often contradict one another. No one theory is sufficiently able to explain the process of aging. The aim of this work is to analyze the different aspects, main characteristics of the aging, individual differences in the speed of this process and theories about the mechanisms of aging.