Hayflick Limit Theory
In 1962 two cell biologists, Dr. Hayflick and Dr. Moorehead, made one of the greatest contributions to the history of cellular biology by demonstrating the senescence of cultured human cells. Hayflick theorized that the aging process was controlled by a biological clock contained within each living cell. The 1961 studies concluded that human fibroblast cells (lung, skin, muscle, heart) have a limited life span. They divided approximately 50 times over a period of years and then suddenly stopped. Nutrition seemed to have an effect on the rate of cell division: overfed cells made up to 50 divisions in a year, while underfed cells took up to three times as long as normal cells to make divisions. Alterations and degenerations occurred within some cells before they reached their growth limit. The most evident changes took place in the cell organelles, membranes and genetic material. This improper functioning of cells and loss of cells in organs and tissues may be responsible for the effects of aging.