The progressive incremental transformation in the form and functionality of human beings and animals, that gradually proceed over time. These changes are not due to illness or random accidents or injuries. These transformations in the form and viability of the human or animal body ultimately result in death.Aging is a process that occurs over time and is gradual decline in the human and animal body that lead to a decline in normal function and appearance.
Aging is a result of changes at the cellular level ( miotic, post miotic, and fibroplast cells) along with bone structure and muscle tissue. These changes manifest themselves with the ultimate decline in key organs ( liver, lungs, kidneys, and heart ).
Also biological systems like the central nervous system, digestive, and reproduction gradually decline leading to the ultimate death of humans and animals.As follows are criteria for aging:
- Cumulative: Gradual signs of aging over time.
- Universal: The entire species show physical evidence of aging.
- Progressive: Aging occurs over an incremental period of time.
- Intrinsic: Aging will occur regardless of the environment humans or animals live in
- Deleterious: Normal biological functions gradually deteriorate over time.