induce replication errors, and this leads to deformed cells and increases the risk of cancer. Genetic Genetic theories of aging propose that aging is programmed within each individual's genes. According to this theory, genes dictate cellular longevity. Programmed cell death, or apoptosis, is determined by a "biological clock" via genetic information in the nucleus of the cell. Genes responsible for apoptosis provide an explanation for cell death, but are less applicable to death of an entire organism. An increase in cellular apoptosis may correlate to aging, but is not a 'cause of death'. Environmental factors and genetic mutations can influence gene expression and accelerate aging. More recently epigenetics have been explored as a contributing factor. The epigenetic clock, which relatively objectively measures the biological age of cells, are useful tool for testing different anti-aging approaches. The most famous epigenetic clock is Horvath's clock, but now already more accurate analogues have appeared. General imbalance General imbalance theories of aging suggest that body systems, such as the endocrine, nervous, and immune systems, gradually decline and ultimately fail to function. The rate of failure varies system by system. Immunological theory The immunological theory of aging suggests that the immune system weakens as an organism ages. This makes the organism unable to fight infections and less able to destroy old and neoplastic cells. This leads to aging and will eventually lead to death. This theory of aging was developed by Roy Walford in 1969. According to Walford, incorrect immunological procedures are the cause of the process of aging. Walford, who stated that his optimized health regime would allow him to live to 120, died of Amytrophic lateral sclerosis at age 79. See also Antagonistic pleiotropy hypothesis Biomarkers of aging Aging and memory Old age Research into centenarians Longevity escape velocity List of life extension topics Timeline of senescence research References attribution contains material copied from Gerontology. Biogerontology Life extension