Aging: Process of becoming older
Ageing or aging (see spelling differences) is the process of becoming older. The term refersespecially to human beings, many animals, and fungi, whereas for example bacteria, perennial plants and some simple animals are potentially biologically immortal. In the broader sense, aging can refer to single cells within an organism which have ceased dividing (cellular senescence) or to the population of a species (population ageing).
In humans, aging represents the accumulation of changes in a human being over time and can encompass physical, psychological, and social changes. Reaction time, for example, may slow with age, while knowledge of world events and wisdom may expand. Aging is among the greatest known risk factors for most human diseases: of the roughly 150,000 people who die each day across the globe, about two thirds die from age-related causes.
The causes of aging are uncertain; current theories are assigned to the damage concept, whereby the accumulation of damage (such as DNA oxidation) may cause biological systems to fail, or to the programmed aging concept, whereby internal processes (such as DNA methylation) may cause aging. Programmed aging should not be confused with programmed cell death (apoptosis).
Aging is a common occurrence among most living things and is a permanent gradual physiological cellular decay. Various theories of aging include telomere shortening, generation of free radicals, accumulation of mutations, all of which contribute to this decay.
Antagonistic Pleiotropy consists of mechanisms/traits that are advantageous during childhood and reproductive years but become harmful as we age. These mechanisms can promote aging. For example, oxidative stress induced by reactive oxygen species which causes oxidation of lipids, proteins, and other compounds.
Genetic predisposition coupled with environmental factors, such as the methylation of DNA which causes mutations in gene expression patterns. Developmental outcomes can affect the rate of aging, however, aging and development do not refer to the same processes. Different environmental stresses and influences can change developmental path of an organism it also changes how the organism ages on an individual scale.
Development is defined as the stage of life when functional change is positive. Functional change during development is characterized by growth and physical maturation. This stage includes childhood all the way to puberty, where individuals reach reproductive status. The developmental theory of aging poses that aging is a programmed molecular mechanism that is essential for embryonic maturation that eventually results in aging phenotypes.