Senescence is the process of aging, both in whole organisms (organismal senescence) and individual cells (cellular senescence) within these organisms. In the strictest scientific sense, senescence means the period of decline that follows the development phase in an organism’s life. This word is derived from the Latin word senex meaning “old age”. In the longevity and healthy aging fields, senescence is the decline in health and function associated with aging. The process of senescence is incredibly complex, and accompanied with a myriad of chemical and physical reactions. As organisms age, they slowly break down, experiencing tissue death and more general malfunction, whether they are plants, animals, fungi, or one-celled organisms. Without the processes of senescence, organisms would be immortal and the Earth would be choked with living organisms as a result. From a biological standpoint, senescence promotes evolution, and keeps Earth from being too crowded.Senescence occurs when cells lose the ability to divide because of DNA damage or a shortening of telomeres, they go through a transformation that results in decline or destruction. The cells either self-destruct (called apoptosis) or go into a period of decline (called senescence). The end result is cell death. Cell death is a normal part of biological functioning and occurs regularly in all living organisms. The science of biological aging is known as biogerontology.