We are born, we grow up, we age, and then we die. Unless disease or trauma occurs, most humans go through the various stages of the life described above. Human Development is the process of growing to maturity and mental ability. Traditionally, theories that explain senescence have generally been divided between the programmed and stochastic theories of aging. Programmed theories imply that aging is regulated by biological clocks operating throughout the life span. This regulation would depend on changes in gene expression that affect the systems responsible for maintenance, repair and defense responses. Stochastic theories blame environmental impacts on living organisms that induce cumulative damage at various levels as the cause of aging. Examples of range from damage to DNA, damage to tissues and cells by oxygen radicals (widely known as free radicals countered by the even more well known antioxidants), and cross-linking.
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