 Human adulthood encompasses psychological adult development.Definitions of adulthood are often inconsistent and contradictory; a person may be biologically an adult, and have adult behavior but still be treated as a child if they are under the legal age of majority.Conversely, one may legally be an adult but possess none of the maturity and responsibility that may define an adult, the mental and physical development and maturity of an individual is proven to be greatly influenced by the circumstances in which they exist.