Aging Aging is the process of aging. It is defined in evolutionary medicine “as a decline with age in the intrinsic capacity to survive and reproduce” (Stearns, 64). Aging can be influenced by natural selection. Natural selection is the mechanism by which an organism best adapted to its environment will survive and pass on more and more beneficial traits to generations. For example, some animals are able to catch their own prey, while others cannot. If an animal develops a trait that helps it survive, it will pass it on to its young, causing that trait to become widespread in the population. Intrinsic and extrinsic factors help understand and measure aging. Intrinsic is the result of aging. When extrinsic mortality rates increase, they decrease the probability of survival and cause a more rapid decline in the strength of selection with age, which increases intrinsic morality rates with age. Age is defined as the lifespan of a person or thing. Aging well means maintaining your physical and mental health as you age. Age is marked by certain stages, aging well can be seen as freedom from illness and active engagement in life. Some lifestyle choices when it comes to aging well can include exercising and dieting. Aging affects our hair, skin, heart, muscles and more, but aging well is possible if we incorporate a healthy lifestyle. There are two mechanisms involved in aging. This involves proton leak and telomere damage. Proton leak occurs when growth rate and metabolic rate cause an increase in energy flow. When these genes are involved in energy metabolism, it could cause aging. The telomere is a protective cap located at the end of chromosomes that shortens with each cell division. When they deteriorate, subsequent cell divisions unsuccessfully replicate subsequent cell divisions. When a woman stops ovulating and menstruating, there is a loss of fertility. There are at least four hypotheses about the evolution of menopause. They are the mother, the grandmother, the by-product and the self-domestication. The mother's hypothesis ceases to reproduce because the risk of dying in childbirth increases with age. The grandmother hypothesis claims that the grandmother can help her daughter raise her grandchildren. Byproduct claims that menopause evolved through oocyte quality control and self-domestication claims that post-reproductive life results from improved survival caused by social and agricultural behavior.