Aging cells (first of 3 images). Light micrograph of a culture of cells which have been genetically- engineered to age rapidly. The cells are seen here in an early phase of their life, and are dividing to produce new cells. The reasons behind aging are complex, and include genetic, physiological and environmental factors. One of the best known causes of aging is the Hayflick effect, in which certain types of cells are genetically programmed to divide only a limited number of times before they die. Magnification: x400 at 35mm size. (See photo's G200/067 and G200/068 for aging sequence to death).