The damage or error theory include 1) Wear and tear theory. Cells and tissues have vital parts that wear out resulting in aging. Like components of an aging car, parts of the body eventually wear out from repeated use, killing them and then the body. So the wear and tear theory of aging was first introduced by Dr. August Weismann, a German biologist, in 1882, it sounds perfectly reasonable to many people even today, because this is what happens to most familiar things around them. 2) Rate of living theory. The greater an organism’s rate of oxygen basal metabolism, the shorter its life span (5). The rate-of-living theory of aging while helpful is not completely adequate in explaining the maximum life span (6).Dr. Rollo proposes a modified version of Pearl’s rate of living theory emphasizing the hard-wired antagonism of growth (TOR) and stress resistance (FOXO) (7). 3) Cross-linking theory. The cross-linking theory of aging was proposed by Johan Bjorksten in 1942 (8). According to this theory, an accumulation of cross-linked proteins damages cells and tissues, slowing down bodily processes resulting in aging. Recent studies show that cross-linking reactions are involved in the age related changes in the studied proteins (9). 4) Free radicals theory. This theory, which was first introduced by Dr. Gerschman in 1954, but was developed by Dr. Denham Harman (10, 11), proposes that superoxide and other free radicals cause damage to the macromolecular components of the cell, giving rise to accumulated damage causing cells, and eventually organs, to stop functioning. 5) Somatic DNA damage theory. DNA damages occur continuously in cells of living organisms. While most of these damages are repaired, some accumulate, as the DNA Polymerases and other repair mechanisms cannot correct defects as fast as they are apparently produced. In particular, there is evidence for DNA damage accumulation in non-dividing cells of mammals. Genetic mutations occur and accumulate with increasing age, causing cells to deteriorate and malfunction. In particular, damage to mitochondrial DNA might lead to mitochondrial dysfunction. Therefore, aging results from damage to the genetic integrity of the body’s cells.