Aging Aging is the process of getting older. It is defined in Evolutionary Medicine “as a decrease with age in the intrinsic ability to survive and reproduce” (Stearns, 64). Aging can be influenced by natural selection. Natural selection is the mechanism by which an organism that is best adapted to its environment will survive and pass on its beneficial traits in increasing numbers to generations. For example, some animals are capable of catching their own prey while others are not. If an animal acquires a characteristic that helps it survive, it will pass it on to its young, resulting in the widespread presence of that characteristic in the population. Intrinsic and extrinsic helps understand and measure aging. The intrinsic is the result of aging. When extrinsic mortality rates increase, they reduce the probability of survival and cause the strength of selection to decline more rapidly with age, increasing rates of intrinsic morality with age. Age is defined as the length of time a person has lived or a thing has existed. Aging well means maintaining your physical and mental health as you age. Age is marked by certain phases, aging well can be considered freedom from disease and active engagement in life. Some lifestyle choices for aging well can be exercise and diet. Getting older affects our hair, skin, heart, muscles and more, but aging well is possible if we incorporate a healthy lifestyle. There are two mechanisms that mediate aging. They are proton losses and telomere damage. Proton loss occurs when growth rate and metabolic rate cause an increase in energy flow. When these genes mediate energy metabolism it could cause aging. The telomere is a protective cap at the end of chromosomes that shortens with each cell division. As they deteriorate, subsequent cell divisions unsuccessfully duplicate the cell. When the woman stops ovulating and menstruating, a loss of fertility occurs. There are at least four hypotheses on the evolution of menopause. They are the mother, the grandmother, the by-product and the self-domestication. The mother hypothesis stops reproducing because the risk of dying in childbirth increases with age. The grandmother hypothesis states that the grandmother can help her daughter raise her grandchildren. Byproduct claims that menopause evolved through quality control of oocytes, and self-domestication claims that post-reproductive life is the result of improvements in survival caused by social and agricultural behavior.